Terra Mission (EOS/AM-1)
Terra (formerly known as EOS/AM-1) is a joint Earth observing mission within NASA's ESE (Earth Science Enterprise) program between the United States, Japan, and Canada. The US provided the spacecraft, the launch, and three instruments developed by NASA (CERES, MISR, MODIS). Japan provided ASTER and Canada MOPITT. The Terra spacecraft is considered the flagship of NASA's EOS (Earth Observing Satellite) program. In February 1999, the EOS/AM-1 satellite was renamed by NASA to "Terra". 1) 2) 3) 4)
The objective of the mission is to obtain information about the physical and radiative properties of clouds (ASTER, CERES, MISR, MODIS); air-land and air-sea exchanges of energy, carbon, and water (ASTER, MISR, MODIS); measurements of trace gases (MOPITT); and volcanology (ASTER, MISR, MODIS). The science objectives are:
• To provide the first global and seasonal measurements of the Earth system, including such critical functions as biological productivity of the land and oceans, snow and ice, surface temperature, clouds, water vapor, and land cover;
• To improve the ability to detect human impacts on the Earth system and climate, identify the "fingerprint" of human activity on climate, and predict climate change by using the new global observations in climate models;
• To help develop technologies for disaster prediction, characterization, and risk reduction from wildfires, volcanoes, floods, and droughts
• To start long-term monitoring of global climate change and environmental change.
Complemented by aircraft and ground-based measurements, Terra data will enable scientists to distinguish between natural and human-induced changes.
Figure 1: Illustration of the Terra spacecraft (image credit: NASA)
Terra consists of a spacecraft bus built by Lockheed Martin Missiles and Space (LMMS) in Valley Forge, PA. The spacecraft is constructed with a truss-like primary structure built of graphite-epoxy tubular members. This lightweight structure provides the strength and stiffness needed to support the spacecraft throughout its various mission phases. The zenith face of the spacecraft is populated with equipment modules (EMs) housing the various spacecraft bus components. The EMs are sized and partitioned to facilitate pre-launch integration and test of the spacecraft.
EPS (Electrical Power Subsystem): A large single-wing solar array (size of 9 m x 5 m = 45 m2), deployed on the sunlit side of the spacecraft, maximizes both its power generation capability and the cold-space FOV (Field of View) available to instrument and equipment module radiators. The average power of the satellite is 2.53 kW provided by a GaAs/Ge solar array (max of 7.5 kW @ 120 V at BOL). The solar array is based on on a prototype lightweight flexible blanket solar array technology developed by TRW (use of single-junction GaAs/Ge photovoltaics). A coilable mast is used for the deployment of the solar array. The Terra spacecraft represents the first orbiting application of a 120 VDC high voltage spacecraft electrical power system implemented by NASA. A PDU (Power Distribution Unit) has been designed to provide 120 DC (±4%) under any load conditions. This regulated voltage, in turn, is achieved via a sequential shunt unit (SSU) and the 2 BCDUs. A NiH2 (nickel hydrogen) battery is used (54 cells series connected) to provide power during eclipse phases of the orbit. 5) 6) 7)
Figure 2: Coilable mast deployer for the Terra solar array (image credit: NASA)
GN&C (Guidance Navigation and Control) subsystem: Terra is a three-axis stabilized design with a single rotating solar array. The GN&C subsystem is made up of sensors, actuators, an ACE (Attitude Control Electronics) unit, and software. A three-channel IRU (Inertial Reference Unit) determines body rates in all control modes. Solid-state star trackers provide fine attitude updates, processed by a Kalman filter to maintain precise 3-axis inertial knowledge. A 3-axis magnetometer senses the Earth's geomagnetic field, primarily for magnetic unloading of reaction wheels, but also as a sensor to determine an attitude failure during a deep space calibration maneuver. 8)
The backup sensors include an ESA (Earth Sensor Assembly) for roll and pitch sensing, and coarse sun sensors for pitch and yaw sensing of the sun line relative to the solar array. A fine sun sensor is used in the event that one star tracker fails or during the backup stellar acquisition mode. In addition to these sensors, a gyro-compassing computation is performed for backup yaw attitude determination.
A reaction wheel assembly provides primary attitude control. During normal mode, a wheel speed controller is available to bias the wheel speeds at a range that avoids zero rpm crossings (stagnation point). Magnetic torquer rods regulate the wheel momentum to < 25% capacity in four-wheel mode and < 50% capacity in the three-wheel mode (backup mode). Thrusters are used for attitude control during all velocity change maneuvers and for backup attitude control and wheel momentum unloading.
GN&C is a fault-tolerant system that includes an FDIR (Fault Detection, Isolation and Recovery) capability unique to each of the different operational control modes. If an attitude fault is detected, FDIR transfers all control functions to the ACE unit configured to use all redundant hardware. Once in safe mode, FDIR is disabled.
Table 1: Overview of GN&C sensors and actuators
Figure 3: Artist' view of the Terra spacecraft in orbit (image credit: NASA)
The design life of the Terra spacecraft is six years. The spacecraft bus is of size of 6.8 m (length) x 3.5 m (diameter) and has a total launch mass of 5,190 kg. The total payload mass is 1155 kg.
RF communications: The primary Terra telemetry data transmissions are via TDRS (Tracking & Data Relay Satellite) system. A steerable HGA (High Gain Antenna) and associated electronics are mounted on a deployed boom extending from the zenith side of the spacecraft. This location maximizes the amount of time available for TDRS communications via this antenna without obstruction by other pads of the spacecraft. Emergency communication is done via the nadir or zenith omni antenna. Command and engineering telemetry data are transmitted in S-band. The science data recorded onboard are transmitted via Ku-band at 150 Mbit/s. The nominal mode of operation is to acquire two 12 minute TDRSS contacts per orbit. During each TDRSS contact, both S-band and Ku-band transmission is being used.
The average data rate of the payload is 18.545 Mbit/s (109 Mbit/s peak); onboard recorders for data collection of one orbit. Mission operations are performed at GSFC. 9)
Broadcast of data: Besides Ku-band and S-band communication, Terra is also capable of downlinking science data via X-band. The X-band communication can be operated in three different modes, Direct Broadcast (DB), Direct Downlink (DDL) and Direct Playback (DP). DB and DDL is used to directly transmit real-time MODIS and ASTER science data respectively to users.
The DAS (Direct Access System) provides a backup option for direct transmission in X-band. DAS supports transmission of data to ground stations of qualified EOS users around the world. These users fall into three categories:
- EOS team participants and interdisciplinary scientists
- International meteorological and environmental agencies
- International partners who require data from their EOS instruments
Figure 4: The Terra spacecraft in the cleanroom of LMMS at Valley Forge (image credit: LMMS)
Launch: The launch of the Terra spacecraft took place on Dec. 18, 1999 from VAFB, CA, on an Atlas-Centaur IIAS rocket.
Orbit: Sun-synchronous circular orbit, altitude = 705 km, inclination = 98.5º, period = 99 minutes (16 orbits per day, 233 orbit repeat cycles). The descending nodal crossing is at 10:30 AM.
Orbit determination is performed by TONS (TDRS Onboard Navigation System) which estimates Terra's position and velocity, drag coefficient, and master oscillator frequency bias. TONS is updated by Doppler measurements at the spacecraft's receivers and provides the attitude control software with a desired pointing ephemeris. Ground-based orbital elements are uplinked daily for backup navigation.
As of March 1, 2001, the Landsat-7, EO-1, SAC-C and Terra satellites are flying the so-called "morning constellation" or "morning train" (a loose formation demonstration of a single virtual platform). There is 1 minute separation between Landsat-7 and EO-1, a 15 minute separation between EO-1 and SAC-C, and a 1 minute separation between SAC-C and Terra. The objective is to compare coincident observations (imagery) from various instruments (synergistic effects). 10)
• July 7, 2018: Northeast of Africa's Kalahari Desert and southeast of the Okavango Delta lies one of the largest salt pans in the world. It was once the site of one of the largest inland seas on Earth. 11)
- For much of the year, the salt pans glimmer in white, parched by the sun and the salt and allowing little more than algae to grow. But during the rainy season (roughly November to March), the area can be transformed into a crucial wetland. Water can flow in from the Boteti and Nata rivers, filling ephemeral ponds, watering holes, and shallow lakes and creating short-lived but abundant grasslands. The event draws migrating wildebeest and zebras, as well as the predators that hunt them. The waters fill with ducks, geese, pelicans, and flamingos—one of just two breeding spots in southern Africa for the long-legged birds.
- The pans are the salty remains of ancient Lake Makgadikgadi. Scientists estimate that the inland sea once spanned anywhere from 80,000 to 275,000 km2. The Okavango, Zambezi, and Cuando rivers likely emptied into this lake until tectonic shifts changed the elevation of the landscape and a changing climate dried up the rains.
Figure 5: On June 10, 2018, the MODIS instrument on NASA's Terra satellite acquired this natural-color image of the Makgadikgadi Salt Pans. The collection of salt flats covers roughly 30,000 km2 amidst desert and dry savanna in Botswana. Located in Makgadikgadi National Park and Nxai Pan National Park, the salt pans are rivaled in extent only by the Salar de Uyuni in Bolivia (image credit: NASA Earth Observatory, image by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response, story by Mike Carlowicz)
• June 5, 2018: Powerful Earth-observing instruments aboard NASA's Terra and Aqua satellites, launched in 1999 and 2002, respectively, have observed nearly two decades of planetary change. Now, for the first time, all that imagery—from the first operational image to imagery acquired today—is available for exploration in Worldview. 12) 13)
Table 2: Interactively explore your world your way with nearly 20 years of MODIS global imagery and the EOSDIS Worldview data visualization application
• On May 28, 2018, a series of potent dust storms swept across Iran, Turkmenistan, Afghanistan, and Pakistan. Accuweather reported winds approaching hurricane-force of 110 km/hr—near the city of Zabol in eastern Iran. Visibility dropped to zero at several points during the storms that lasted up to 12 hours in some places. News media claimed that as many as 100 people were injured across the region. 14)
- Meteorologists noted that the late-May dust storms were "caused by a strong upper level storm system that tracked north of the region, bringing thunderstorms to Turkmenistan and northern Afghanistan, but just producing powerful winds in eastern Iran." SST (Sea Surface Temperatures) in the Arabian Sea have been about 1.5 to 2º C above normal in May, which could be contributing to the development of potent winds and storm fronts blowing across the Middle East and India this spring.
- Iran is mostly arid or semiarid, with deserts making up at least 25 million hectares (250,000 km2) of the country's area. That already dry landscape has been parched by drought over the past year. Iranian environmental officials recently reported that 18 wetlands have completely dried up in recent months, and another 24 are in critical condition. Lake Urmia has been affected by warmer weather and drier than normal conditions over the past few decades. Such conditions have increased the amount of sand and dust available to be picked up by strong winds.
- Several governments and international groups have been looking for solutions to ease the region's water and dust problems, which are partly due to drought and global warming, but also attributed by some scientists to uneven water management practices (irrigation, storage, treatment, and groundwater pumping). In the meantime, the Iranian government recently reported that it would be spreading petroleum-based mulch across 46,000 hectares of the desert this year in order to cut down on dust pollution.
Figure 6: MODIS on NASA's Terra satellite acquired this image of the dust storms on May 28, 2018. Such storms, sometimes known as haboobs, are dramatic events associated with weather fronts, and they often appear as walls of sand and dust marching across the landscape. Like thunderstorms, haboobs tend to abrupt and short-lived (image credit: NASA Earth Observatory, image by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response, story by Mike Carlowicz)
• On May 3, 2018, a new eruption began at a fissure of the Kilauea volcano on the Island of Hawaii. Kilauea is the most active volcano in the world, having erupted almost continuously since 1983. Advancing lava and dangerous sulfur dioxide gas have forced thousands of residents in the neighborhood of Leilani Estates to evacuate. A number of homes have been destroyed, and no one can say how soon the eruption will abate and evacuees can return home. 15)
Figure 7: On May 6, 2018, at approximately 11 a.m. local time, the MISR (Multi-angle Imaging SpectroRadiometer) instrument on the Terra satellite captured this view of the island as it passed overhead. Much of the island was shrouded by clouds, including the fissure on its eastern point. However, an eruption plume is visible streaming southwest over the ocean. The MISR instrument is unique in that it has nine cameras that view Earth at different angles: one pointing downward, four at various angles in the forward direction, and four in the backward direction. This image shows the view from one of MISR's forward-pointing cameras (60º), which shows the plume more distinctly than the near-vertical views (image credit: NASA)
- The information from the images acquired at different view angles is used to calculate the height of the plume, results of which are superimposed on the right-hand image. The top of the plume near the fissure is at about 2,000 m altitude, and the height of the plume decreases as it travels south and west. These relatively low altitudes mean that the ash and sulfur dioxide remained near the ground, which can cause health issues for people on the island downwind of the eruption. The "Ocean View" air quality monitor operated by the Clean Air Branch of the State of Hawaii Department of Health recorded a concentration of 18 µg/m3 of airborne particles less than 2.5 µm in diameter at 11 a.m. local time. This amount corresponds to an air quality rating of "moderate" and supports the MISR results indicating that ash was most likely present at ground level on this side of the island.
- These data were acquired during Terra orbit 97780. The smoke plume height calculation was performed using the MISR MINX (INteractive eXplorer) software tool, which is publicly available at https://github.com/nasa/MINX. The MISR Plume Height Project maintains a database of global smoke plume heights, accessible at https://www-misr.jpl.nasa.gov/getData/accessData/MisrMinxPlumes2/.
• May 07, 2018: Loktak Lake is not only the largest freshwater lake in northeast India, it is also home to unique floating islands called "phumdis." These circular landmasses are made of vegetation, soil, and organic matter (at different stages of decomposition) that has been thickened into a solid form. The islands have a spongy surface that feels like a trampoline. Like an iceberg, most of the mass of phumdis lies below the water surface. During the dry season, when water levels drop, the living roots of the islands can reach the lakebed and absorb nutrients. 16)
- Speckled across this Loktak Lake, the several thousand phumdis and its surrounding waters are vital for irrigation, drinking water, food supplies, thus the lake has been referred as the "lifeline of Manipur" state. Thousands of fishermen make their livelihood in the waters, catching about 1,500 tons of fish every year. Children and illiterate adults also attend a school located on one of the floating islands.
- The phumdis support around 200 species of aquatic plants and 400 species of animals, including the rare Indian python. The largest island is home to the Keibul Lamjao, the world's only floating national park. It serves as a habitat for the endangered brow-antlered sangai, or "dancing deer," whose hooves have adapted to the island's spongy ground. The park, covering 40 km2, was specifically created to preserve the deer, which were once thought to be extinct. The habitat is composed of floating meadows and a raised strip of hard ground that separates the park into northern and southern zones.
- The construction of the Ithai Dam in the 1980s — built to provide power for India's northeast states — has threatened the life of the islands. The dam south of Loktak Lake has caused water levels to remain high year-round, preventing the phumdis from sinking and reaching the lakebed for nutrients. As a result, the phumdis are slowly thinning and breaking apart.
Figure 8: The satellite images of Loktak Lake (Figures 8 and 9) were acquired on March 19, 2018, by ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) on the Terra satellite (image credit: NASA Earth Observatory, images by Joshua Stevens, using data from NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team, story by Kasha Patel)
Figure 9: Overview image of Loktak Lake in India (image creedit: NASA Earth Observatory)
- Sediment loads tend to be especially heavy in the western end of Lake Erie. Of all the Great Lakes, Erie usually has the most sediment loading because of extensive farmland and cities near its shores. Since it is also the shallowest of the lakes, winds and currents can easily stir up sediments (quartz sand and silt, as well as calcium carbonate from limestone) on the lake bottom. And farmland, particularly fields that lack winter cover crops, tends to give up large amounts of sediment to rivers and streams.
- The situation is similar around Saginaw Bay, part of Lake Huron. More than half of the land surrounding the bay is used for agriculture, so spring runoff generally carries very large amounts of sediment.
- Landsat-8 and Sentinel-2 recently captured higher-resolution images of sediment in Saginaw Bay as well.
Figure 10: MODIS on NASA's Terra satellite captured this image on April 20, 2018. After the storm, bloated rivers and streams dumped sediment-rich water into the lakes. Brisk spring winds combined with lake currents to send tendrils of mud and other debris swirling into deeper, bluer waters (image credit: NASA Earth Observatory, image by Adam Voiland, using MODIS data from LANCE/EOSDIS Rapid Response, story by Adam Voiland)
• April 17, 2018: Crops have withered and ranchers are culling herds after an unusually dry growing season in a country that is among the world's top producers of soybeans and corn. Argentina's soy production is projected to decline 31 percent and corn by 20 percent in 2017–2018 compared to the prior growing season, according to the U.S. Foreign Agricultural Service. 18)
- The economic consequences of the drought have been significant. Since December 2017, corn prices in the U.S. have risen 14 percent, and soybean prices are up 8 percent. Losses in Argentina are expected to surpass $3.4 billion, making the drought the most expensive natural disaster in 2018 so far.
- MODIS is just one of several satellite instruments useful for monitoring drought (Figure 11). The soil moisture maps (Figure 12) were produced with data collected on April 3, 2017, (left) and April 6, 2018, (right) by NASA's SMAP (Soil Moisture Active Passive) satellite. SMAP carries a radiometer that measures soil moisture in the top 5 cm of the ground. Dark green and blue areas are progressively wetter.
Figure 11: The MODIS instrument on NASA's Terra satellite captured these natural-color images of the flat, fertile Pampas region of central Argentina. The Pampas appeared lush and green in April 2017 (left) in contrast to the browner landscapes (right) visible one year later (image credit: NASA Earth Observatory, images by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response. Story by Adam Voiland)
Figure 12: Soil moisture map comparison of Argentina acquired with SMAP on April 3, 2017 (left) and on April 6, 2018 (right), image credit: NASA Earth Observatory, images by Joshua Stevens, using soil moisture data courtesy of JPL and the SMAP Science Team
• March 29, 2018: Days of heavy rains drenched several watersheds in central and northern Queensland in early March 2018. Following the deluge, NASA satellites collected images of the pulse of water as it flowed south through braided rivers in Australia's Channel Country, a desert region known for becoming lush with greenery after floods. 19)
- The MODIS instrument on NASA's Terra and Aqua satellites captured this sequence of six images between March 11 and March 26, 2018. It shows the progress of water (light blue) on the Hamilton, Diamantina, and Thomson Rivers. The images use a combination of infrared and visible light to increase the contrast between water and land.
Figure 13: MODIS on Terra and Aqua acquired this sequence of images between 11-26 March 2018 (image credit: NASA Earth Observatory, images by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response. Story by Adam Voiland)
- These three rivers drain from far to the north into basins near the border with South Australia, where water spreads out in large, shallow lakes. The rivers flow south toward the lowest point in Australia—Lake Eyre—partly because coastal mountain ranges block routes to the sea. As of March 27, 2018, flood water on the Diamantina had flowed as far south as Betoota and had begun to trickle into Birdsville, a remote town on the edge of the Simpson Desert.
- Northern Queensland is still being hammered by heavy rain. As the remnants of a tropical cyclone passed over the region on March 27, some areas received up to 400 mm of rain, according to Australia's Bureau of Meteorology.
• March 10, 2018: In late February 2018, a series of rainstorms pounded the central United States, causing damaging flooding along the Ohio River and parts of the Mississippi. Weeks after the storms, the effects were still being felt as far away as Louisiana. That pulse of flood water traveled down the Mississippi River and, by early March, reached the Gulf of Mexico. 20)
- On March 8, the U.S. Army Corps of Engineers opened the Bonnet Carré Spillway, which diverts excess water from the Mississippi River and relieves pressure on levees downriver in New Orleans. It marks the 12th time that the spillway has been opened since the structure was completed in the early 1930s. "This was a big event, but on the scale of big events, it's a small one," said Alex Kolker, an associate professor with the Louisiana Universities Marine Consortium.
- Still, the flood was substantial enough to color coastal waters brown with suspended sediments. On March 4, 2018, MODIS on NASA's Terra satellite acquired this image of the sediment plume spilling into the Gulf of Mexico.
- According to Nan Walker, director of Earth Scan Laboratory at Louisiana State University, sediment plumes are visible almost every spring. "The biggest floods of the Mississippi River occur on average in March or April," she said, "depending upon the weather over the drainage basin."
- When sediment-laden floodwaters reach the mouth of the Mississippi, they can contribute to land building. That's important because the wetlands in the lower part of the Mississippi River delta, particularly around a sub-delta known as Bird's Foot, are some of the most rapidly sinking wetlands in the country.
- "In order to keep pace with subsidence, you need floods like this one to bring sediment to the mouth of the Mississippi," Kolker said. "Many restoration plans revolve around diverting the flow of the Mississippi River in order to recreate systems like Bird's Foot higher up in the river system. But you need a lot of data to make these decisions when dealing with such a large, complicated hydrological issue."
- Satellite data helps scientists understand the movement of sediment and freshwater into the Gulf. According to Kolker, MODIS is good at telling scientists how a plume gets redirected by winds and currents. It also improves the understanding of plume dynamics—that is, where fresh water, nutrients, and sediments end up.
- When this image was acquired, winds were blowing out of the southeast, pushing the plume of sediment and freshwater to the northwest almost to Grand Isle. "This is the time of year when shrimp are spawning in that bay," Kolker said. "Events like this one can impact their life cycle."
Figure 14: On March 4, 2018, MODIS on NASA's Terra satellite acquired this image of the sediment plume spilling into the Gulf of Mexico (image credit: NASA Earth Observatory, image by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response, story by Kathryn Hansen with image interpretation by Nan Walker and Alex Kolker)
• February 26, 2018: As sea ice at far northern latitudes approached its annual maximum extent, MODIS on NASA's Terra satellite captured this natural-color image of sea ice and clouds off of Canada's Newfoundland and Labrador province. Though sea ice has been significantly below normal extent and thickness across much of the Arctic, the ice in the Labrador Sea has been relatively close to normal. 21)
- In this image, acquired by MODIS on February 18, 2018, the coastline, the sea ice edge, and offshore clouds all present a clear edge to distinguish one from the next. Ice hugs the coast, where it receives the full chilling effect of offshore winds, and the water is shallower and fresher than in the open sea. The swirl patterns on the eastern edges reveal areas where ice is new and has not yet consolidated into a solid sheet, so it is more susceptible to stirring by winds and by ocean eddies.
- The cloud streets to the right indicate strong and cold winds were blowing from west to east from the interior of Labrador. The gap between the ice and the cloud streets occurs because the cold winds need some "fetch" (a distance of open water) to pick up moisture for cloud formation.
- The Labrador Sea is a marginal sea that separates Arctic Canada and Greenland while connecting the North Atlantic Ocean to the Arctic Ocean by way of Baffin Bay and Davis Strait. The area is critical to the formation of cold, deep water masses that help drive circulation in a phenomenon known as "the great ocean conveyor belt."
- The western half of the Labrador Sea is typically covered with ice from December through late spring, though the extent varies considerably with local weather patterns from year to year. As of mid-February 2018, sea ice extent in this region appeared to be near or just above the long-term average, according to maps from NSIDC (National Snow and Ice Data Center). However, conditions in the rest of the Arctic have been grim this winter. In fact, Arctic sea ice reached a record low for the month of January, and conditions have not improved much in February. NSIDC reported Arctic sea ice extent to be 9.4 percent below the 1981–2010 average.
Figure 15: This MODIS image was acquired on 18 Feb. 2018 showing the coastline of Newfoundland and Labrador, the sea ice edge, and offshore clouds all present a clear edge to distinguish one from the next (image credit: NASA Earth Observatory, image by Jeff Schmaltz, LANCE/EOSDIS Rapid Response. Story by Mike Carlowicz, with image interpretation from Walt Meier, NSIDC, and Claire Parkinson, NASA/GSFC)
• February 21,2018: Indonesia's Mount Sinabung has been sporadically active since 2010, following four centuries of quiet. On February 19, 2018, the stratovolcano on the island of Sumatra erupted violently, spewing ash at least 5 to 7 km into the air over Indonesia. At 11:10 a.m. local time (04:10 Universal Time) on February 19, MODIS on NASA's Terra satellite captured a natural-color image of the eruption, just a few hours after it began. 22)
- According to reporting from the Associated Press, the erupting lava dome obliterated a chunk of the peak as it erupted. Plumes of hot gas and ash rode down the volcano's summit and spread out in a 5 km diameter, while ash falls were recorded as far away as the town of Lhokseumawe, some 260 km to the north.
- Villages were coated in ash, and airline pilots were given the highest alert for the region. Government officials handed out face masks to the citizens of the island and advised them to stay indoors due to the potentially dangerous air quality. As volcanologist and blogger Erik Klemetti put it: "breathing volcanic ash is a significant health hazard—the ash is really small shards of glass, so it can abrade your lungs and form a ‘cement.'"
Figure 16: MODIS image on Terra, acquired on 19 Feb. 2018, showing the massive smoke-and-ash column of Mount Sinabung on the island of Sumatra (image credit: NASA Earth Observatory, images by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response, Story by Mike Carlowicz)
- The volcanic plume also contained sulfur dioxide (SO2), which can irritate the human nose and throat when breathed in. The gas reacts with water vapor in the atmosphere to produce acid rain, and it also can react with other gases to form aerosol particles that cause haze and, in extreme events, climate cooling. The map of Figure 17 shows concentrations of SO2 as detected at 1:20 p.m. local time (06:20 Universal Time) on February 19 by the Ozone Mapper Profiler Suite (OMPS) on the Suomi-NPP satellite. Maximum gas concentrations reached 140 Dobson Units.
Figure 17: OMPS (Ozone Mapper Profiler Suite) on Suomi NPP observed the SO2 cloud of the Sinabung eruption, acquired on 19 Feb. 2018 (image credit: NASA Earth Observatory, images by Joshua Stevens, using OMPS data from the Goddard Earth Sciences Data and Information Services Center (GES DISC), Story by Mike Carlowicz)
- Other sensors on NASA satellites have also been monitoring Sinabung. According to data from CALIPSO, some debris and gas from the eruption appear to have risen 15 to 18 kilometers in the atmosphere.
- According to news reports, the dust was carried by winds known as the scirocco. (In North Africa, these same desert winds are known as "chrom" (hot) or "arifi" (thirsty). The warm, dry air mass begins over the Sahara, picks up moisture over the Mediterranean, and moves north toward areas of lower pressure along the coasts of Europe.
- The dust can be seen making its way toward Italy, and then continues to countries to the north (beyond this image). According to local news reports, the winds brought above average temperatures to Italy, while the sand increased the chance of rain. The fine sand particles can act as a "seed" on which water droplets can form fog or fall as rain. In Italy's coastal areas, cars were covered with a layer of dust.
Figure 18: The MODIS instrument on Terra captured on 7 Feb. this image of a Sahara Storm carrying great amounts of sand north over the Mediterranean Sea (image credit: NASA Earth Observatory, images by Jeff Schmaltz, using MODIS data from LANCE/EOSDIS Rapid Response ,caption by Kathryn Hansen)
• January 28, 2018: Winter is a dusty season off the coast of North Africa. As temperatures drop and high pressure builds on the continent, strong winds known as the harmattan blow east across the Sahara. They pick up sand and dust from the desert and loft it over the ocean. In late January, MODIS on NASA's Terra satellite caught a glimpse of Saharan dust bathing the Cape Verde islands, which lie about 650 kilometers off the coast of Senegal. The images were acquired on January 22 and 23. 24)
- Note the wind shadows, wakes, and vortices—areas with less dust density—on the leeward side of the islands. Winds blowing from the northeast and east run into the high volcanic peaks of the islands, which block some of the dust and alter the air flow. Note, too, how much denser the dust plume grows on the second day.
- Hundreds of millions of tons of dust blow out of Africa every year, crossing the Atlantic all the way to the Caribbean and the Gulf of Mexico. This dust fertilizes the ocean with nutrients that can promote plankton growth, but it can also carry fungus and disease-causing microorganisms that damage coral reefs.
Figure 19: MODIS image of Saharan dust, acquired on 22 Jan. 2018, bathing the Cape Verde islands - resulting in wakes and vortices on the leeward side of the islands (image credit: NASA Earth Observatory, images by Joshua Stevens and Jeff Schmaltz, using MODIS data from LANCE/EOSDIS Rapid Response. Story by Mike Carlowicz and Holli Riebeek)
Figure 20: MODIS image of Saharan dust, acquired on 23 Jan. 2018, bathing the Cape Verde islands - Note, how much denser the dust plume grows on the second day (image credit: NASA Earth Observatory, images by Joshua Stevens and Jeff Schmaltz, using MODIS data from LANCE/EOSDIS Rapid Response. Story by Mike Carlowicz and Holli Riebeek)
• January 24, 2018: Heavy rains and swiftly warming temperatures followed a prolonged cold spell in the Northeastern U.S., leading to a long ice jam that clogged the Connecticut River. MODIS on NASA's Terra satellite collected natural-color (left) and false-color (right) images of the ice on January 18, 2018 (Figure 21). In the false-color image, ice appears light blue, and open water appears black. A second large jam is visible south of Haddam, Connecticut. 25)
Figure 21: MODIS images of the Connecticut region acquired on 18 January 2018 (image credit: NASA Earth Observatory image by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response, caption by Adam Voiland)
- On the same day, the MSI (Multi Spectral Imager) on the European Space Agency's Sentinel-2 satellite acquired the data for a natural-color image (Figure 22) of the ice jam. Iced-over parts of the river are white; open water is green.
- The ice jam extended several miles upstream from Haddam. Much of it was made up of brash ice—a sturdy type that forms when thinner ice layers are pushed on top of each other and then frozen together by cold weather. Often brash ice on rivers includes tree limbs and other debris that make it difficult for ice cutters to break it.
- Three U.S. Coast Guard cutters capable of breaking ice are working in the area. Cheers went up from the shores of the river as the boats arrived and began to break up the jam on January 23, the Coast Guard tweeted.
- Ice jams can block the natural flow of rivers and cause water levels to rise behind them. On January 23, the river level was 2 m at Middle Haddam—high enough to cause minor flooding. National Weather Service forecasters expect the river to crest at 2.6 m on January 24.
Figure 22: MSI natural-color image on Sentinel-2 of the Connecticut River ice jam captured on 18 Jan. 2018 (image credit: NASA Earth Observatory using modified Copernicus Sentinel data (2018) processed by the European Space Agency, caption by Adam Voiland)
• January 14, 2018: Sitting along the northwest rim of the Pacific Ring of Fire, Kamchatka is one of the most volcanically active parcels of land in the world. At least 300 volcanoes dot the peninsula, and at least 29 of them are active. 26)
- Two of those volcanoes were busily puffing away in early January 2018. MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite caught a glimpse of plumes rising from Shiveluch and Klyuchevskaya on January 9 (Figure 23). The plume from Shiveluch stretched for at least 100 km. Note the long shadows, which are caused by high peaks and thick clouds and the low, oblique angle of the Sun in the winter sky.
Figure 23: The MODIS instrument on Terra observed the plumes rising from the Shiveluch and Klyuchevskaya volcanos on January 9 (image credit: NASA Earth Observatory, image by Joshua Stevens and Jeff Schmaltz, using MODIS data from LANCE/EOSDIS Rapid Response. Story by Michael Carlowicz)
Figure 24: Detail OLI image of the Klyuchevskaya volcano, acquired on 10 January, 2018 (image credit: NASA Earth Observatory, image by Joshua Stevens and Jeff Schmaltz, using Landsat data from the USGS, Story by Michael Carlowicz)
- Shiveluch is one of the largest and most active volcanoes on the Kamchatka Peninsula, with at least 60 eruptions in the past 10,000 years. The current eruption has been ongoing since 1999. On January 10, 2018, the Kamchatka Volcanic Eruption Response Team reported that volcanic explosions had lofted ash 10 to 11 km into the atmosphere. The aviation threat level was briefly raised to code red, but was lowered to orange by the end of the day. Volcanic emissions can pose a hazard to airplane engines, which can stall or fail when choked with smoke and ash.
- By comparison, Klyuchevskaya was relatively docile on January 10, emitting a small plume of gas, steam, and ash. The volcano is the tallest and most active on the peninsula, and the latest eruption has been ongoing since August 2015. More than 100 eruptions have occurred at Klyuchevskaya in the past 3,000 years, with 12 eruptions since 2000.
Figure 25: Overview image of OLI of the Klyuchevskaya volcano, acquired on 10 January, 2018 (image credit: NASA Earth Observatory, image by Joshua Stevens and Jeff Schmaltz, using Landsat data from the USGS, Story by Michael Carlowicz)
• January 9, 2018: After a powerful nor'easter dumped snow across a thousand miles of the U.S. East Coast, yet another blast of bitterly cold air spilled into the region and drove already low temperatures even lower. 27)
- Statisticians and meteorologists had plenty to tally as city after city broke daily low temperature records, but perhaps the most dramatic sign of the extreme cold emerged offshore. Many rivers, bays, and estuaries along the coast froze over, including some that only rarely have ice.
- MODIS (Moderate Resolution Imaging Spectroradiometer) on Terra captured this trio of images on January 7, 2018. Figure 26 shows ice in Delaware Bay—between New Jersey, Pennsylvania, and Delaware—and the northern part of the Chesapeake Bay between Maryland and Delaware. Figure 27 shows ice in the Albemarle Sound in North Carolina, and Figure 28 shows Rhode Island and southeastern Massachusetts.
- The U.S. Coast Guard warned mariners of icy conditions and started operations to break up ice in some areas. Basins and waterways that are shallow and less salty, such as coastal rivers and estuaries, tend to freeze before deeper, saltier water (while fresh water freezes at 32°F (0°C), seawater freezes at 28 °F.)
- On January 7, 2018, several cities experienced record low temperatures, according to the National Weather Service. Temperatures dropped to -20 degrees Fahrenheit (-29 Celsius) in Burlington, Vermont; -11°F (-24 ºC) in Portland, Maine; -2°F (-19ºC)in Boston, Massachusetts; -9°F (-22ºC) in Hartford, Connecticut; 2°F (-19ºC) in Wilmington, Delaware; 1°F (-17ºC) in Baltimore, Maryland; and 4°F (-15ºC) in Raleigh, North Carolina.
Figure 26: MODIS image of Delaware Bay—between New Jersey, Pennsylvania, and Delaware acquired on 7 Jan. 2018 (image credit: NASA image by Jeff Schmaltz, LANCE/EOSDIS Rapid Response. Image cropping and caption by Adam Voiland)
Figure 27: MODIS image of the Albemarle Sound in North Carolina acquired on 7 Jan. 2018 (image credit: NASA image by Jeff Schmaltz, LANCE/EOSDIS Rapid Response. Image cropping and caption by Adam Voiland)
Figure 28: MODIS image of Rhode Island and southeastern Massachusetts, with ice in Buzzards Bay and Nantucket Sound, acquired on 7 Jan. 2018 (image credit: NASA image by Jeff Schmaltz, LANCE/EOSDIS Rapid Response. Image cropping and caption by Adam Voiland)
• January 4, 2018: It is frigid in much of Canada and the Midwestern and Eastern United States. Daily low-temperature records have dropped like snowflakes. New Year's polar plunges have been canceled due to the cold, and many people in the Southeast are in a battle to keep their pipes from freezing. 28)
- In the Western U.S., Alaska, Europe, and Asia—not so much. December and January have been abnormally warm for most of the world. People in California have been worrying about wildfires in what should be the wet season, and Alaskans are ice skating in T-shirts.
Figure 29: MODIS land surface temperature map of North America, acquired in the period 26 Dec. 2017 to 2 Jan. 2018 (image credit: NASA Earth Observatory maps by Jesse Allen, based on MODIS land surface temperature data provided by the Land Processes Distributed Active Archive Center. Story by Adam Voiland)
- This temperature anomaly map is based on data from MODIS on NASA's Terra satellite. It shows land surface temperatures (LSTs) from December 26, 2017 to January 2, 2018, compared to the 2001–2010 average for the same eight-day period. Red colors depict areas that were hotter than average; blues were colder than average. White pixels were normal, and gray pixels did not have enough data, most likely due to excessive cloud cover. Note that it depicts land surface temperatures, not air temperatures. Land surface temperatures reflect how hot the surface of the Earth would feel to the touch in a particular location. They can sometimes be significantly hotter or cooler than air temperatures. (To learn more about LSTs and air temperatures, read: Where is the Hottest Place on Earth?)
- The map of North America underscores one of the realities of weather—when a cold snap hits one region, warmth often bakes another one. A giant meander (or Rossby wave) in the jet stream is the common thread that connects the warm weather west of the Rockies with the chill east of them. As the crest of a Rossby wave—a ridge—pushed unusually far toward Alaska in December, it dragged warm tropical air with it. In response, the other side of the wave—a trough—slid deep into the eastern United States, bringing pulses of dense, cold Arctic air south with it. The Rocky Mountains have boxed in much of the coldest, densest air, serving as a barrier between the cold and warm air masses.
- Even as the Eastern U.S. freezes, comparatively balmy conditions are dominating many other parts of the world. Europe, much of Asia, and the Middle East have been abnormally warm. In the southern hemisphere, Antarctica, eastern Australia, southern Africa, and the Horn of Africa have been warmer than usual, while the Amazon in South America, the Sahara in Africa, and western Australia were cool.
Figure 30: MODIS land surface temperature map of the world, acquired in the period 26 Dec. 2017 to 2 Jan. 2018 (image credit: NASA Earth Observatory maps by Jesse Allen, based on MODIS land surface temperature data provided by the Land Processes Distributed Active Archive Center. Story by Adam Voiland)
• December 21, 2017: It is rare for large wildfires to burn in California in December, which is usually a wet month for the state. In most years, a few hundreds acres might burn. The 2006 Shekell fire in Ventura charred 13,600 acres, making it the largest December fire in the state between 2000 and 2016. — In 2017, the Thomas fire shattered the record for December and may soon eclipse the worst blaze in any month. After burning for 16 days, the massive fire had scorched 272,000 acres (110,000 hectares or 425 square miles) and was just 60 percent contained. That made it the second largest fire on record in California, trailing only the Cedar fire, which burned 273,246 acres in 2003. 29)
- OLI (Operational Land Imager) on Landsat-8 captured an image of the Thomas fire scar on December 18, 2017. The natural-color Landsat-8 image was draped over an ASTER-derived Global Digital Elevation Model, which shows the topography of the area. The fire raged first near Ventura, then burned the hills around communities of Ojai and Oak View. Firefighters put up a fierce fight and managed to prevent flames from descending into the valley towns. Flames then pushed west toward Summerland, Montecito, and Santa Barbara. As of December 20, the fire was still spreading along the northern edge of the burn scar.
- Authorities reported that more than 1,200 structures—most of them in Ventura County—have been destroyed. Several factors came together to make the blaze difficult to control. An usually wet winter and spring in early 2017 caused vegetation to flourish. Then the dry season turned out to be excessively dry, and rains also have been scarce in the typically wetter months of November and December. All of that vegetation dried out and was primed to burn. Once the fire started, warm temperatures and unusually fierce Santa Ana winds caused the fire to spread rapidly.
- After nearly two weeks of red flag conditions, a break in the weather has allowed firefighters to beat back the flames in the past few days. But fire officials still do not expect the Thomas fire to be completely contained until January 2018.
- After nearly two weeks of red flag conditions, a break in the weather has allowed firefighters to beat back the flames in the past few days. But fire officials still do not expect the Thomas fire to be completely contained until January 2018.
Figure 31: OLI on Landsat-8 captured an image of the Thomas fire scar on December 18, 2017. The natural-color Landsat-8 image was draped over an ASTER-derived Global Digital Elevation Model which shows the topography of the area (image credit: NASA Earth Observatory image by Joshua Stevens, using Landsat data from the USGS and ASTER GDEM data from NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team, story by Adam Voiland)
• December 19, 2017: Peat is a soil-like mixture of partly decayed plant material that builds up in wetlands, swamps, and partly submerged landscapes. When it gets dried out or burned, it can be a significant source of greenhouse gases such as carbon dioxide and methane. 30)
- As the world continues to warm and human activities deplete and degrade wetlands and peatlands in many parts of the world, scientists and policymakers would like to have a better understanding of the volume of the world's peat deposits. However, past estimates have varied significantly.
- Earlier this year, researchers from the Sustainable Wetlands Adaptation and Mitigation Program offered new maps of peat extent and depth in the tropics. The scientists based their findings on a mixture of satellite, climate, and topographic data collected in 2011 that, when merged in a computer model, made it possible to generate better maps of the extent and depth of peatlands. The high resolution of the model meant they could identify peat-forming areas that were often omitted in previous mapping efforts—peat found under dense forest canopies, peat formed in areas that are only wet for part of the year, and other small deposits.
- Using their new approach, the researchers concluded that South America accounts for 46 percent of the global total of tropical peat and holds more than Asia (previously considered to be the largest source). Brazil, not Indonesia, led the world in tropical peatland area, with the Amazon Basin being the largest contributor of tropical peat. They also found new hot spots in Africa, with ten times more peat than was reported in previous estimates.
- The maps of Figures 32 and 33 show peatland depth in South America. Areas with the deepest peat are shown with dark orange. Thinner deposits are shown with lighter shades of orange and yellow. Most of the new stores of peat were found to be in relatively shallow deposits in the Amazon basin, particularly along the Rio Negro and Rio Branco.
- "The Rio Negro headwaters suffer from El Niño droughts, and large fires are known to affect the region. Some of these fires are likely affecting peat deposits, which would result in much larger greenhouse gas emission than previously thought for the region," said Rosa Maria Roman-Cuesta, a Center for International Forestry Research (CIFOR) scientist involved in the project.
- Areas mapped as having peat had to meet three conditions. They had to have enough water, according to rainfall and evapotranspiration data. A satellite sensor—the Moderate Resolution Imaging Spectroradiometer (MODIS)—had to observe wet surfaces for a prolonged period. And the terrain, based on information from the Shuttle Radar Topographic Mission, had to be able to retain water.
Figure 32: Overview map showing the peatland deposits in South America, acquired in 2011 with MODIS on Terra and Aqua and with SRTM (Shuttle Radar Topography Mission), acquired in 2000 (image credit: NASA Earth Observatory, image by Jesse Allen using data from Gumbricht, T., et al. (2017), story by Adam Voiland) 31)
Figure 33: Detail map of the Amazon basin, particularly along the Rio Negro and Rio Branco (image credit: NASA Earth Observatory, image by Jesse Allen using data from Gumbricht, T., et al. (2017), story by Adam Voiland)
• December 7, 2017: Thick smoke was streaming from several fires in southern California when the MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite acquired a natural-color image in the afternoon on December 5, 2017. 32)
- The largest of the blazes—the fast-moving Thomas fire in Ventura County—had charred more than 65,000 acres (24,000 hectares or 94 square miles), according to Cal Fire. Smaller smoke plumes from the Creek and Rye fires are also visible.
Figure 34: MODIS image of the Ventura County fire acquired on 5 Dec. 2017 (image credit: NASA Earth Observatory, images by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response, story by Adam Voiland)
- On the same day, the MSI (Multi Spectral Imager) on the Sentinel-2 satellite of ESA captured the data for a false-color image (Figure 35) of the burn scar. Active fires appear orange; the burn scar is brown. Unburned vegetation is green; developed areas are gray. The Sentinel-2 image is based on observations of visible, shortwave infrared, and near infrared light.
- The fires mainly affected a forested, hilly area north of Ventura, but flames have encroached into the northern edge of the city. On December 6, 2017, Cal Fire estimated that at least 12,000 structures were threatened by fire.
Figure 35: MSI image of the Ventura County fire acquired on 5 Dec. 2017 (image credit: ESA, the image contains modified Copernicus Sentinel data (2017) processed by the European Space Agency)
- Powerful Santa Ana winds fanned the flames. Forecasters with the Los Angeles office of the National Weather Service warned that the region is in the midst of its strongest and longest Santa Ana wind event of the year. They issued red flag warnings for Los Angles and Ventura counties through December 8, noting that isolated wind gusts of 130 km/hr are possible.
- A prolonged spell of dry weather also primed the area for major fires. This week's winds follow nine of the driest consecutive months in Southern California history, NASA/JPL ( Jet Propulsion Laboratory) climatologist Bill Patzert told the Los Angeles Times. "Pile that onto the long drought of the past decade and a half, [and] we are in apocalyptic conditions," he said.
• December 5, 2017: Frigid air blowing from Eastern Russia created dramatic cloud formations over the Sea of Okhotsk in late November, 2017. The MODIS instrument aboard NASA's Terra satellite acquired a true-color image of the stunning scene on November 25 (Figure 36). 33)
- Snow covers the land of Eastern Russia in the west of this image, with a large bank of cloud overlying the land in the northwest. Long parallel rows of cumulus clouds blow off the snow-covered area and over the blue waters of the Sea of Okhotsk. These rows of cloud, known as "cloud streets" form as cold, dry air from the land blows across relatively warmer, much moister ocean water and create cylinders of spinning air. Where the air is rising, small clouds form. Where the air is descending, the skies are clear. The cloud streets align along the direction of the wind movement.
Figure 36: MODIS on Terra captured this true-color image of a stunning cloud formation scene over the Sea of Okhotsk on 25 November, 2017 (image credit: Jeff Schmaltz, MODIS Land Rapid Response Team, NASA/GSFC)
• November 28, 2017: The coastal waters along China's Jiangsu province are brown all year round due to the large volume of suspended sediment that flows out from the Yangtze, Yellow, and other rivers. 34)
- But every winter, an even larger tongue of sediment emerges over the Great Yangtze Bank and extends hundreds of kilometers into the East China Sea. These winter plumes are prominent features in satellite imagery for a few months, before fading away in the spring. MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite captured this natural-color image of a plume over the Great Yangtze Bank on November 9, 2017 (Figure 37).
- Remote sensing scientists find the feature perplexing and have advanced several theories about the causes. Some have argued that the plume is a product of currents moving sediment-laden river water eastward from the coast. Others have argued that it is caused by tides lifting up sediment that was deposited on the bottom of the Great Yangtze Bank hundreds of years ago.
- A new study in the Journal of Geophysical Research Oceans makes the case for the latter option. After gathering data on waves, sediments, and currents as observed in January 2016 (when the sediment plume was visible in satellite imagery), researchers developed a model that simulated conditions in this part of the ocean. They ran a series of computational experiments that showed that the energy of tides is strong enough to stir up bottom sediment from the Yangtze Bank.
- The tides do this all year round, the scientists think, but their modeling shows that the sediment can only rise up to the surface in the winter, when temperatures and salinities at the sea surface and bottom are roughly the same. In the summer, an influx of fresh water from the Yangtze, combined with heating of the surface layers of the sea, prevents vertical mixing and keeps the resuspended sediment in the depths.
Figure 37: MODIS natural-color image of a plume over the Great Yangtze Bank on November 9, 2017 [image credit: NASA Earth Observatory image by Jesse Allen, using data from the Level 1 and Atmospheres Active Distribution System (LAADS). Story by Adam Voiland, with information from Zhifa Luo (East China Normal University)]
• October 11, 2017: Parts of northern California have been ravaged by intense and fast-burning wildfires that broke out on October 8, 2017. Blazes that started on a few hundred acres around Napa Valley were fanned by strong northeasterly winds, and by October 10, the 14 fires had consumed as much as 100,000 acres (150 square miles) of land. States of emergency have been declared in Napa, Sonoma, Yuba, and Mendocino counties, and thousands of people were asked to evacuate. The densely populated "wine country" is famous for its vineyards and wine-making operations and the tourists they attract. 35)
- In the late morning of October 9, MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite acquired a natural-color image of the smoke billowing from the fires (Figure 38).
- CalFire and local officials reported that at least 1,500 homes and businesses have been destroyed, and thousands more are being threatened. In some places, entire neighborhoods burned to the ground. Cellular and land-line phone communications have been lost in several areas. Authorities are still accounting for deaths and people reported missing. As of the morning of October 10, none of the fires were even partially contained, according to CalFire bulletins.
- While the causes of the fires are still under investigation, we do know what helped them spread quickly: abundant dried vegetation and seasonal wind patterns. "After more than a decade of drought, the fuel levels—dry brush and grasses—across California are exceptionally high," said William Patzert, a climatologist at NASA's Jet Propulsion Laboratory. "Last winter's welcome rains created more vegetation that, over the past six months, created more fuel."
- The fall season also typically brings hot, dry, and gusty winds. These Diablo winds are driven by atmospheric high-pressure systems over the Great Basin (mostly in Nevada). Winds blow from northeast to southwest over California's mountain ranges and down through the valleys and coastal regions. These downslope winds can quickly whip up a fire and carry burning embers to the next neighborhood or patch of woodland.
- "The simple formula is fuel-plus-meteorology-plus-ignition equals fire. The catalyst is people," Patzert added. "The fires erupted in areas where wildlands meet urban and suburban development. Californians have built in what are historical fire corridors, and these high-density developments are particularly vulnerable to fast-moving, destructive fires."
Figure 38: MODIS on Terra acquired this image of the fire regions in northern California in the late morning of 9 October 2017 (image credit: NASA Earth Observatory, image by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response. Story by Mike Carlowicz)
• September 8, 2017: During the monsoon season, heavy rains regularly pummel South Asia. But the summer monsoon of 2017 was different. In August 2017, day-after-day of punishing rainfall caused catastrophic flooding in northern India, Nepal, and Bangladesh. 36)
- More than 40 million people in the three countries have been afflicted. Hundreds of villages have been submerged, and tens of thousands of homes have been destroyed. Millions of people are living in refugee camps, and vast tracts of farmland and grazing land has been inundated.
- One of the hardest hit areas is Bihar, a state in East India with a vast expanse of flat, fertile land. Flooding grew severe there after heavy rains on August 10, 2017. By September, nearly 17 million people in that state alone had been affected by floods, according to the United Nations Office for the Coordination of Humanitarian Affairs. Roughly 7,000 villages in Bihar have flooded and more than 700,000 people have been displaced.
Figure 39: MODIS on the Terra satellite acquired this image of the Ganges, Koshi, and several other rivers on September 6, 2017, when flood water covered large swaths of the landscape (image credit: NASA Earth Observatory, images by Jesse Allen, using data from LAADS (Level 1 and Atmospheres Active Distribution System), story by Adam Voiland)
Figure 40: This MODIS image on Terra shows the same area on May 24, 2017, before monsoon rains began (image credit: NASA Earth Observatory, images by Jesse Allen, using data from LANCE (Land Atmosphere Near real-time Capability for EOS), story by Adam Voiland)
• September 2, 2017: On August 31, 2017, MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite acquired a false-color image (top) of extensive flooding along the Texas coast and around the Houston metropolitan area in the aftermath of Hurricane Harvey. A second image shows the same area on August 20, four days before the storm made landfall. 37)
- Both images were made with a combination of visible and infrared light (MODIS bands 7-2-1) that highlights the presence of water on the ground. Water is generally dark blue or black in this type of image, but rivers also can appear light blue because they carry large amounts of suspended sediment. Turn on the image-comparison tool to spot areas that have been inundated by rainwater and coastal surges.
- On August 31, MODIS also captured natural-color images of the area. Note the tan and brown rivers and bays full of flood water from Harvey. Scientists and civil authorities have some concerns about urban and industrial pollutants being mixed into the floodwater runoff. Along the coast, muddy, sediment-laden waters from inland pour into the Gulf of Mexico, which also was churned up by the relentless storm.
- According to the National Weather Service, 51.88 inches (131.8 cm) of rain were recorded at Cedar Bayou, Texas—the highest rainfall total for any storm in recorded U.S. history. Meteorologists at The Washington Post noted that that is as much rain as usually falls in Houston in an entire year and in Los Angeles in four years. By most accounts, Harvey produced more cumulative rainfall than any storm in the U.S. meteorological record — as much as 24 trillion gallons of water (unofficial estimates).
- In addition to providing satellite imagery and data of the storm, NASA has started flying its UAVSAR (Uninhabited Aerial Vehicle Synthetic Aperture Radar) aboard a Gulfstream III aircraft to collect high-resolution radar observations over rivers, flood plains, and critical infrastructure. That data can be compared and combined with SAR data from satellites such as the Sentinel- 1A and 1B missions of ESA.
Figure 41: False-color image of MODIS, acquired on Aug. 31, 2017, showing extensive flooding along the Texas coast and around the Houston metropolitan area in the aftermath of Hurricane Harvey (image credit: NASA Earth Observatory, images by Jesse Allen, using data from LANCE (Land Atmosphere Near real-time Capability for EOS), Story by Mike Carlowicz)
Figure 42: Detail image of the Houston region (image credit: NASA Earth Observatory, images by Jesse Allen, using data from LANCE (Land Atmosphere Near real-time Capability for EOS), Story by Mike Carlowicz)
• September 1, 2017: What remains of the large inland lake is a fraction of what it was in the 1950s and 60s. In those years, the government of the former Soviet Union diverted so much water from the Amu Darya and Syr Darya—the regions's two major rivers—to irrigate farmland, that it pushed the hydrologic system beyond the point of sustainability. During subsequent decades, the fourth largest lake in the world shrank to roughly a tenth of its former size and divided into several smaller bodies of water. 38)
- The image of Figure 43, captured by MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite, shows the Aral Sea in Central Asia on August 22, 2017. While the lake is much smaller in August 2017 than it was in the 1960s, some growth in the eastern lobe of the South Aral represents an improvement over August 2014, when that lobe was completely dry.
- Instead of pooling in one large basin, water flowing down the two rivers now ends up in either the North Aral Sea (fed by the Syr Darya) or the South Aral Sea (fed by Amu Darya). The Kok-Aral dike and dam, finished in 2005, separates the two water bodies and prevents flow out of the North Aral into the lower-elevation South Aral. The dam has actually led fisheries in the North Aral Sea to rebound, even as it has limited flow into the South basin.
- Managers use a sluice gate to let some water flow from the North Aral into the South Aral. During wet and snowy years, these releases are common; in dry years, they are rare. In 2017, heavy outflow from the North Aral in the winter, spring, and summer caused the eastern lobe of the South Aral to partially refill, explained Philip Micklin, a geographer emeritus from Western Michigan University.
- Large releases from the Toktogul Dam, a reservoir on a tributary of the Syr Darya, increased the flow of the Syr in the winter. In the spring, unusually warm temperatures melted enough snow pack and glacial ice in the Tien Shan to keep the river high. To a lesser degree, flow from the Amu Darya may have contributed to the partial replenishment of the eastern lobe in 2017 as well.
- The images of Figures 44 and 45 show the pathway water follows as it flows down the Syr Darya, into the North Aral Sea, and eventually the South Aral Sea. OLI (Operational Land Imager) on Landsat-8 collected the images on August 5, 2017. At the time, the sluice gates at the dam appeared to be open, and water was flowing past the Tsche-Bas Gulf and into the South Aral.
- "However, this year's events do not signal a restoration of the eastern lobe as a permanent feature," said Micklin. "Since the early 2000s, the eastern lobe revitalizes during heavy flow years and then dries completely, or nearly completely in low flow years. I see this process continuing for the foreseeable future."
Figure 43: MODIS image of the Aral Sea in Russia, acquired on August 22, 2017 (image credit: NASA Earth Observatory image by Jesse Allen, using Terra MODIS data from the LANCE (Land Atmosphere Near real-time Capability for EOS), Story by Adam Voiland)
Figure 44: This detail image the the Aral Sea was acquired on Aug. 5, 2017, with OLI on Landsat-8 (image credit: NASA Earth Observatory image by Jesse Allen,using Landsat-8 data from the USGS, Story by Adam Voiland)
Figure 45: A further detail image of the North Aral Sea was acquired on Aug. 5, 2017 with OLI on Landsat-8. At the time, the sluice gates at the Kok-Aral Dam appeared to be open, and water was flowing past the Tsche-Bas Gulf and into the South Aral Sea ( (image credit: NASA Earth Observatory image by Jesse Allen,using Landsat-8 data from the USGS, Story by Adam Voiland)
• August 27,2017: Goldstrike mine in northeastern Nevada is one of the largest gold mines in the world. In 2016, the mine produced 1.1 million ounces of gold (corresponding to 34,100 kg). Only two other operations—the Grasberg mine in Indonesia and the Muruntau mine in Uzbekistan—produced more. 39)
- On September 25, 2016, ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) on NASA's Terra satellite captured this false-color image of the mine (Figure 46). Vegetation appears red. Water is dark blue. Bare rock appears in shades of brown and gray. The most noticeable feature is the Betze-Post open-pit mine, which is managed by Barrick Gold Corporation and has a depth of more than 500 meters. Smaller open-pit mines operated by other companies are also visible northwest and southeast of the Betze-Post pit.
- Trucks transport ore from the bottom of the pit to nearby processing facilities, where gold is concentrated and extracted. On average, there is roughly 0.1 ounce of gold per ton of ore. Processing typically involves crushing ore into powder, exposing it to high temperatures and pressures, and leaching material out of liquid slurries. Leftover slurry is stored in tailing ponds, where solids settle out. In addition to its large open-pit mine, Goldstrike has two underground mines that also produce ore.
- One of the key issues facing mines is water management. Open-pit mining requires pumping groundwater out of adjacent aquifers in order to prevent the pit from flooding. At Goldstrike, operators pump several thousand gallons of groundwater per minute to keep the water table below the level of the pit. Some of this water is used to process ore, but some of it gets used in other ways or pumped backed into the ground. For instance, the water used to irrigate the circular fields southwest of the Betze-Post pit comes from groundwater pumping related to the mining.
- While the company that operates Goldstrike mine maintains a network of monitoring wells and stream gages to track how mine activities are affecting the aquifer, it also has used InSAR (Interferometric Synthetic Aperture Radar) data from satellites as part of its monitoring efforts. Since each monitoring well can cost between $300,000 to $500,000, and InSAR offers a big-picture view of the aquifer, a satellite perspective can offer an effective way of monitoring subsidence, uplift, and other changes in the Earth's crust associated with groundwater pumping, the company noted. InSAR observations show subsidence in areas near the mines and uplift in areas southwest of the mines.
Figure 46: ASTER image of the Goldstrike mine in northeastern Nevada, acquired on September 25, 2016 (NASA Earth Observatory, image by Jesse Allen, using data from NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team, story by Adam Voiland)
• August 19, 2017: NASA's Terra satellite was built to observe Earth, and for more than 17 years its imagers have looked downward for 24 hours a day, collecting images needed to study the planet's surface, oceans, and atmosphere. However, the satellite recently trained its eyes on a different celestial body. 40) 41)
- On August 5, 2017, Terra made a partial somersault, rotating its field of view away from Earth to briefly look at the Moon and deep space. This "lunar maneuver" was choreographed to allow the mission team to recalibrate Terra's imagers—MODIS (Moderate Resolution Imaging Spectroradiometer), ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer), and MISR (Multi-angle Imaging SpectroRadiometer). The Terra operations team last made such a maneuver in 2003.
- The orbital gymnastics are necessary for radiometric calibration; that is, making sure MODIS, MISR, and ASTER are properly recording the amount of light emitted and reflected by surfaces on Earth. In the harsh environment of space, satellite instruments are bombarded by high-energy particles, cosmic rays, and strong ultraviolet light, and this inevitably leads to degradation in the sensors over time. If changes in sensitivity are not properly accounted for, the images would start to make it appear as if Earth were growing darker or lighter—which would throw off scientific efforts to characterize air pollution, cloud cover, and other elements of the environment.
- The lunar surface provides a good eye test for the imagers. "The Moon is like a standard candle or lamp: the amount of energy from it is well known," said Kurt Thome, project scientist for Terra. "If you look at it periodically, it allows you to see if your instruments are changing over time."
- Since the Moon's surface brightness has been stable over the 17-year life of the mission—and, in fact, for thousands of years—the images of the lunar surface can be used as a standard for calibration. Terra can also observe the Moon without any atmospheric effects (such as turbulence, scattering, and absorption), which can add significant uncertainty in measured values.
- The image of Figure 47 was acquired by ASTER, while MODIS acquired the a further image. MODIS has actually been looking at the Moon monthly for nearly its entire mission, but MISR and ASTER do not have this capability or proper angles for such a view. "MODIS can peek out of the corner and get a view of the Moon," Thome said. "For MODIS, it has been a great way to understand the instrument over its lifetime and notice any changes."
Figure 47: ASTER image of the moon acquired on August 6, 2017 (image credit: NASA, images by Michael Abrams, Abbey Nastan, and Jesse Allen)
Figure 48: MISR images of the moon acquired on August 6, 2017 (image credit: NASA, images by Michael Abrams, Abbey Nastan, and Jesse Allen; Story by Tassia Owen, Abbey Nastan, and Michael Carlowicz)
- The nine images of Figure 48 come from MISR's nine imagers. The MISR operations team uses several methods to calibrate the data regularly, all of which involve imaging something with a known (or independently measured) brightness and correcting the images to match that brightness. Every month, MISR views two panels of a special material called Spectralon, which reflects sunlight in a very particular way. ASTER, meanwhile, views a set of lamps that light up its reflective bands. Periodically, this calibration is checked by a team on the ground that measures the brightness of a flat, uniformly colored surface on Earth (such as a dry desert lakebed) while MISR and ASTER fly overhead. The lunar maneuver offers a third opportunity to check the brightness calibration of MISR.
- When viewing Earth, MISR's cameras are fixed at nine different angles, with one (called An) pointed straight down, four pointed forwards (Af, Bf, Cf, and Df) and four angled backwards (Aa, Ba, Ca, and Da). The A, B, C, and D cameras have different focal lengths, with the most oblique (D) cameras having the longest focal lengths in order to preserve spatial resolution on the ground. During the lunar maneuver, however, the spacecraft rotated so that each camera saw the almost-full Moon straight on. This means that the different focal lengths produce images with different resolutions (D cameras produce the sharpest). These grayscale images were made with raw data from the red spectral band of each camera.
- After 17 years of collecting valuable data and dwindling fuel supplies, Terra is nearing the end of the mission, but not before it double-checks its data one last time. The lunar calibration is important not only for the accuracy of Terra's instruments, but also providing data that are used to calibrate other satellites (including weather).
- The phenomenon of sunglint is a matter of optics. Areas where the sea surface is smoother reflect more sunlight directly back to the satellite's imager. In contrast, areas of rougher water appear darker because light is scattered in many more directions.
- Dry, cool winds from the north, called the Etesian winds, are common over the Aegean Sea during summer. On the windward side of the islands, those winds pile up the water and disturb the surface. But as those air masses run into the islands and their rocky peaks, a "wind shadow" with much calmer winds (and seas) form on the leeward side of islands (in this case, the south sides). Darker areas amid the bright streaks could be the result of wind or water turbulence, or perhaps breaks in the wind-blocking land topography.
Figure 49: Sunglint image of the Aegean islands, acquired with MODIS on July 6, 2017 (image credit: NASA Earth Observatory, image by Jeff Schmaltz, caption by Kathryn Hansen)
• July 5, 2017: Icy lakes and rivers make a significant footprint on the Arctic landscape. Though widely dispersed, lakes cover as much as 40 to 50 percent of the land in many parts of the Arctic, and seasonal lake and river ice covers roughly 2 percent of all of Earth's land surfaces. Since lakes and rivers have the highest evaporation rate of any surface in high latitudes, understanding and monitoring seasonal ice cover is critical to accurately forecasting the weather and understanding regional climate processes. 43)
- Lake and river ice also affects the people who live in the Arctic. Seasonal ice roads serve as a key transportation route for many communities. Ice jams can produce sudden and dangerous hazards to hydroelectric power facilities, infrastructure, and human settlements. Changing ice conditions make shipping and boating a challenge. And ice is involved in a range of hydrological processes that can affect the quality of drinking water.
- Nonetheless, lake and river ice generally gets the least attention from ice scientists. According to one analysis, scientists publish roughly 50 scientific articles related to lake or river ice each year. In comparison, well over 600 articles get written about glaciers, 500 about snow, 350 about sea ice, and 250 about permafrost.
- Satellites could help fill this gap. In fact, since the number of ground-based ice monitoring stations has declined since the 1980s, satellites offer one of the most promising means of monitoring lake and river ice over large areas, noted the authors of a book chapter about the state of lake and river ice research.
- On May 29, 2017, MODIS on NASA's Terra satellite captured this image of ice covering the Amundsen Gulf, Great Bear Lake, and numerous small lakes in the northern reaches of Canada's Northwest Territories and Nunavut. Sea ice generally forms in the Gulf of Amundsen in December or January and breaks up in June or July. Lake and river ice in this area follow roughly the same pattern, though shallow lakes freeze up earlier in the fall and melt earlier in the spring than larger, deeper lakes.
Figure 50: On May 29, 2017, MODIS on NASA's Terra satellite captured this image of ice covering the Amundsen Gulf, Great Bear Lake, and numerous small lakes in the northern reaches of Canada's Northwest Territories and Nunavut (image credit: NASA Earth Observatory, image by Joshua Stevens, using MODIS data, story by Adam Voiland)
• May 14, 2017: Strong desert winds in mid-May 2017 lofted a huge dust plume from western Africa and carried it over the Atlantic Ocean. At 12:10 UTC on May 9, 2017, the MODIS (Moderate Resolution Imaging Spectroradiometer) instrument on NASA's Terra satellite acquired this natural-color image of airborne sand and other aerosols. The plume stretched southwest to the Cabo Verde (Cape Verde) islands and beyond (Figure 51). 44)
- Africa is the world's largest source of dust to the atmosphere, contributing about 70 percent of the global total. Airborne mineral dust from the world's deserts delivers nutrients to the land and ocean, and affects the atmosphere and climate.
Figure 51: A dust storm over western Africa acquired by MODIS on May 9, 2017 (image credit: NASA Earth Observatory, image by Jeff Schmaltz)
• April 30, 2017: It might look like something mysterious is happening in the waters off of Oman, but this dark, sinuous shape has a completely natural explanation. On April 11, 2017, the MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite captured this natural-color image of the Arabian Sea (Figure 52). 45)
- Smooth water reflects sunlight like a mirror, particularly when viewed from above. Areas where that light is reflected by the water at the same angle that a satellite views it—when the Sun, the satellite, and the sea are lined up—appear brighter than surrounding areas. Viewed globally, sunglint shows up as long, linear streaks down the center of a swath of satellite data.
- This image shows a detailed view of sunglint in the Middle East. What's interesting is that the sunglint (bright area) is interrupted. Dark areas indicate surface waters that have been roughened by wind, causing sunlight to reflect in many directions. That means less light is reflected directly back toward the satellite. In this way, sunglint can be used to discern phenomena like wind patterns that are not directly visible in natural-color imagery.
Figure 52: A large Sunglint region in the Arabian Sea interrupted by dark ares of wind-roughened surface waters. This image was acquired on April 11, 2017 with the MODIS instrument (image credit: NASA Earth Observatory, image by Jeff Schmaltz, text by Kathryn Hansen)
• March 28, 2017: A long-dormant volcano on Russia's Kamchatka Peninsula erupted in March 2017. Several satellites caught images of a thick, ash-laden plume trailing from Kambalny. MODIS on NASA's Terra satellite captured a natural-color image of the Kambalny Volcano and its plume on March 25, 2017, the day after it began to erupt. By 1:34 p.m. local time (01:34 Universal Time) that day, the plume stretched about 100 km to the southwest (Figure 53). A dark stain is visible to the west of the plume, where ash has covered the snow. By March 26, ash falls would cover the ground on both sides of the volcano. 46)
- OMI ( Ozone Monitoring Instrument) on on NASA's Aura satellite observed an airborne plume of sulfur dioxide (SO2) trailing south of Kamchatka on March 26 (Figure 54). "The higher SO2 amounts downwind could be due to multiple factors," said Simon Carn, an atmospheric scientist at Michigan Technological University, "including variable emissions at the volcano (such as an initial burst), increasing altitude of the plume downwind, or decreasing ash content downwind."
- Invisible to the human eye, SO2 can harm people as well as the environment. According to a recent study, volcanoes collectively emit 20 to 25 million tons of SO2 into the atmosphere per year.
- An alert from the Kamchatka Volcanic Eruption Response Team warned of sporadic ash plumes rising up to 8 km above sea level. The activity could affect international and low-flying aircraft in the region, the group said.
Figure 53: MODIS image of the Kambalny ash plume, captured on March 26, 2017 (01:34 UTC), image credit: NASA Earth Observatory, image by Jeff Schmaltz and Joshua Stevens)
Figure 54: OMI image of the Kambalny ash plume, acquired on March 26, 2017 (image credit: NASA Earth Observatory, image by Joshua Stevens)
• March 26, 2017: New Zealand's Tasman Glacier is a massive block of ice, but it is no bulwark. The longest glacier in the country is neither immovable nor permanent. Instead, it continues to shrink by the day. 47)
- In Figure 55, captured on December 30, 1990, by the TM (Thematic Mapper) on the Landsat-4 satellite, the Tasman Glacier stretched like a serpentine tongue. The image of Figure 56 was acquired on January 29, 2017, by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA's Terra satellite. Both false-color images use white to show frozen snow or ice, and blue for water. Brown represents bare ground, while red areas are covered in vegetation.
- In the 26 years between images, the ice has retreated an average of 180 meters per year, according to New Zealand's National Institute of Water and Atmospheric Research. Before 1973, Tasman Lake did not exist. In the past decade, it has swollen to a length of 7 km. The lake growth is a direct result of the glacier's decline. The Tasman Glacier retreated 4.5 km from 1990 to 2015 mostly through calving, according to Mauri Pelto, a glaciologist at Nichols College. Researchers have predicted the lake will "increase dramatically in the near future" as the glacier produces more meltwater. The footprint of nearby Murchison Lake (below Murchison Glacier) has also grown.
- New Zealand is home to more than 3,000 glaciers, many of which are in decline. The Tasman Glacier is one of several that drains into Lake Pukaki, which is used to generate hydroelectric power. Further downstream, the same water feeds the Waitaki River, a habitat to trout and salmon.
Figure 55: Tasman Glacier false-color image of the Thematic Mapper instrument on Landsat-4, acquired on Dec. 30, 1990 (image credit: NASA Earth Observatory, image by Jesse Allen and Joshua Stevens)
Figure 56: Tasman Glacier false-color image of JAXA's ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) on NASA's Terra satellite, acquired on Jan. 29, 2017 (image credit: NASA Earth Observatory, image by Jesse Allen and Joshua Stevens)
• February 21, 2017: Heat waves are not unusual in Australia. A subtropical belt of high pressure that flows over the continent regularly delivers pulses of hot, dry air to the surface in the summer. Yet even by Australian standards, the intense heat wave of February 2017 has been remarkable. 48)
- When a high-pressure system stalled over central Australia, extreme temperatures emerged first in South Australia and Victoria and then spread to New South Wales, Queensland, and Northern Territory. With overheated bats dropping from trees and bushfires burning out of control, temperatures smashed records in many areas.
- Figure 57 shows peak land surface temperatures between February 7 and 14, 2017, a period when some of the most extreme heating occurred. The map is based on data collected by MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite. Note that it depicts land surface temperatures, not air temperatures. Land surface temperatures reflect how hot the surface of the Earth would feel to the touch in a particular location. They can sometimes be significantly hotter or cooler than air temperatures.
- On February 12, 2017, air temperatures rose to 46.6°C in the coastal city of Port Macquarie, New South Wales, breaking the city's all-time record by 3.3º C. Two days earlier, the average maximum temperature across all of New South Wales hit a record-setting 42.4°C — a record that was broken the next day when it rose to 44.0°C. In some places, the duration of the heatwave has been noteworthy. Mungindi, a town on the border of Queensland and New South Wales, endured 52 days in a row when maximum temperatures exceeded 35°C — a record for New South Wales.
- Many scientists see exceptional heat waves like this as part of a broader trend. For instance, one study published by the Climate Council of Australia concluded that heatwaves — defined as at least three days of unusually high temperatures — grew significantly longer, more intense, and frequent between 1971 and 2008.
Figure 57: MODIS on Terra acquired this image map of Australian land surface temperatures in the period Feb. 7-14, 2017 (image credit: NASA Earth Observatory, image by Jesse Allen, caption by Adam Voiland)
• February 12, 2017: Covering about 400,000 hectares (4000 km2) in Iran's Khuzestan province, the Shadegan wetlands are the largest in Iran (Figure 58). At their center is Shadegan Pond, a large but shallow body of water surrounded by a varied landscape of sugar plantations, date palm orchards, small towns, and military fortifications. The Karun River winds along its western edge. Fields of sugar cane stand northwest of it. The town of Shadegan—which is flanked by long, narrow orchards — lies to its east. 49)
- Environmental conditions at the wetlands vary throughout the year. In the fall and winter, rains in the Zagros Mountains send water flooding through an intricate series of shallow lagoons and marshes. Many of these areas dry out during the summer months. This image was acquired in the fall, when the area was relatively dry.
- The Shadegan wetlands support an array of living things. Sheep, cattle, and water buffalo roam the area, while Mesopotamian himri, carp, and catfish are commonly caught in the pond's waters. Dozens of bird species—including several types of ducks, terns, gulls, and egrets—can be found in Shadegan Wildlife Refuge.
- The refuge is one of the most important sites in the world for the marbled teal, a diving duck. Shadegan supports about 10,000 to 20,000 of these birds in the winter, about half of the world's population.
Figure 58: Image of the Shadegan Pond in Iran, acquired on September 3, 2012 with the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) of JAXA on the NASA's Terra satellite (image credit: NASA Earth Observatory image by Jesse Allen, caption by Adam Voiland)
• January 11, 2017: In January 2007, satellites captured an extraordinary example of hole-punch clouds visible over the southern United States. But occurrences of the cloud type, albeit usually less pronounced, show up every year over Earth's mid- and high-latitudes. A more recent display developed over eastern China, visible in the image of Figure 59, acquired on December 28, 2016, with MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite. 50)
- This strange phenomenon results from a combination of cold temperatures, air traffic, and atmospheric instability. If you were to look from below, it would appear as if part of the cloud was falling out of the sky. As it turns out, that's actually what's happening.
- The mid-level clouds are initially composed of liquid drops at a super-cooled temperature below 0° Celsius. As an airplane passes through the cloud, it creates a disturbance that triggers freezing. Ice particles then quickly grow in the place of the water droplets. Eventually the ice crystals in these patches of clouds grow large enough that they literally fall out of the sky—earning hole-punch clouds their alternate name: "fallstreak holes." Falling crystals are often visible in the center of the voids.
- The formations in this image are less like holes and more linear, like long canals. The same basic processes are responsible for producing both configurations. Whether the void takes on a circular or linear shape depends on differences such as cloud thickness, wind shear, and air temperature. Hole-punch and canal clouds can appear together, as they did in this image from December 2015. They often occur in the vicinity of an airports.
Figure 59: The MODIS instrument on Terra acquired this image on Dec. 28, 2016 over eastern China showing the display of canal clouds (image credit: NASA Earth Observatory, image by Joshua Stevens,caption by Kathryn Hansen)
• On November 24, 2016, Tokyo received its first November snowfall in more than half a century. The MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite captured this natural-color image the same day. The snow fell in and around the Japanese capital, coating the metropolitan area and accumulating along some sidewalks (Figure 60). 51)
- Figure 61, a false-color image from MODIS on Terra, shows a stark contrast between snow (blue) and clouds (white). The snow traces the contours of surrounding mountains and is distinguishable from clouds offshore. Central Tokyo is gray-brown in color, suggesting less accumulation or faster melting. Urban centers tend to shed snow faster than surrounding countryside because they are often hotter, a result of the urban heat island effect.
- The November dusting was caused by a cold air mass moving down from the Arctic, according to the Japan Meteorological Agency. Meteorologists connected the storm to the Arctic oscillation, a climate pattern that affects the northern hemisphere. Usually, high air pressure in the mid-latitudes prevents colder, low-pressure air seeping down from the Arctic. However, weaker pressure systems occasionally disrupt this barrier, and colder air can penetrate further south, as in this case.
Figure 60: Snow-covered Tokyo region as acquired by the MODIS instrument on November 25, 2016 (image credit: NASA Earth Observatory, image by Joshua Stevens)
Figure 61: False-color image of Tokyo, acquired on Nov. 25, 2016, showing the stark contrast between snow (blue) and clouds (white), image credit: NASA Earth Observatory, image by Joshua Stevens
• Sept. 8, 2016: In August 2016, the return of sunlight on the Antarctic Peninsula meant that the landscape became visible again in natural-color satellite imagery. That's when scientists saw something interesting: a rift along Larsen C—the continent's fourth-largest ice shelf—has grown considerably longer. 52)
- The scenario is similar to what occurred before a calving event and partial collapse of Larsen B in 2002. But exactly what's in store for Larsen C remains to be seen. "We don't know yet what will happen here," said Ala Khazendar of NASA's Jet Propulsion Laboratory.
- Figure 62 was acquired with MISR's downward-looking (nadir) camera. This natural-color image has a red tint due to the steep lighting angle, as the Sun does not reach far above the horizon in August. The ice shelf comprises the left half of the image, and thinner sea ice appears on the right.
- Figure 63 shows the same area. By combining these different angles in one image, one can discern surface roughness. Rougher surfaces appear pink and smoother areas appear purple. The ice shelf is generally smoother than the sea ice, with the exception of the crack—an indication that it is actively growing, according to the MISR team. Project MIDAS, a group in the United Kingdom that has been tracking the rift, reported that the crack grew 22 km over the past six months. It now stretches 130 km.
- Both images show other fissures as well, all of which terminate at about the same distance south of the lengthening crack. "People have been intrigued by this," Khazendar said. "It's quite a remarkable feature, how they open and then seem to stop opening." There are a few hypotheses as to why that happens. The cracks might come to a stop when they reach a suture zone—an area where sectors of ice feeding the shelf are advancing at different speeds, creating shear where they flow together. Ice in this zone is already so fractured that it halts further propagation of the big, crosswise cracks.
- The cracks also could have reached an area where marine ice has formed on the bottom of the ice shelf. Marine ice is relatively warm and less stiff, so it can accommodate higher levels of strain without fracturing. The crack that's actively lengthening, however, has overcome those obstacles. "What's happening now is different," Khazendar said. "This crack goes farther and has started propagating northwards."
- Even before signs of the lengthening appeared at the surface, Khazendar and colleagues suspected something was going on. A study in 2011 that measured ice velocity showed a "line" across the shelf; everything between that line and front of ice shelf was flowing noticeably faster than everything upstream. They proposed that the line traced the location of a crevasse growing upward along the bottom of the ice sheet. Then in 2014, the MIDAS team first detected the rift growing at the surface.
- "What might be happening is that there is enhanced melting at bottom of ice shelf, resulting in the removal of the softer marine ice, allowing fractures to be filled with ocean water," Khazendar said. "When that happens, it could cause pre-existing bottom crevasses to propagate up through the ice shelf."
- Cracks and calving of ice from the front of an ice shelf is a normal process. Shelves are fed by ice coming from glaciers and ice streams from the interior of the continent. They advance into the ocean until a calving event takes place. The shelf front retreats and then advances again. The whole cycle can occur over the span of a few decades. "That's just part of life for an ice shelf," Khazendar said. "That's how they behave."
- In the case of Larsen B, the big calving events took place with a frequency that did not allow enough time for the shelf to re-advance. As a result, the front of the shelf kept retreating in a run up to the big disintegration event that occurred in just six weeks in 2002. "The growing crack on Larsen C could be the beginning of a process that will end up like Larsen B," Khazendar said. "If a big calving event takes place, we will be interested to see how the shelf itself reacts. But all the indications so far are that it is relatively stable, albeit with intimations of change."
Figure 62: The rift is visible in this image acquired on August 22, 2016, with the MISR (Multi-angle Imaging SpectroRadiometer) instrument on Terra (image credit: NASA Earth Observatory images by Jesse Allen and the MISR Team)
Figure 63: Composite image of the same area from MISR's backward-, vertical-, and forward-pointing cameras (image credit: NASA Earth Observatory images by Jesse Allen and the MISR Team)
• July 12, 2016: NASA's Terra satellite observed a large dust storm off the coast of Chile. It is unusual to see such large dust events emerge from the west coast of South America, according to atmospheric scientists. Winds there "are not conducive to developing major dust storms like those that we see in North Africa or in Asia," said Joseph Prospero, an atmospheric scientist at the University of Miami. 53)
- The local topography hinders the formation of dust storms, as the Andes Mountains run along South America's western flank and block winds arising in the east. The mountain range stretches more than 7,000 km from north to south, and stands more than 500 km wide in some areas. Usually, dust storms during this time of year (southern, or austral, winter) will blow eastward toward the Atlantic Ocean, said Santiago Gasso, an aerosol scientist at NASA's Goddard Space Flight Center.
- Globally, natural sources account for roughly 75 percent of dust emissions, while anthropogenic (manmade) sources account for roughly 25 percent, according to research published in Reviews of Geophysics. On July 8, the source was natural. The image of Figure 64 suggests that the dust source is located between the Andes and the Pacific coast. The slice of land there is narrow, with steeply rising walls. The dust source could be on an elevated slope, making it easier for dust to lift and travel far. It also could be driven by low-level winds—possibly katabatic winds, which blow downslope off the continent. The term katabatic comes from the Greek "katabaino," meaning "to descend." Such winds develop as air that comes in contact with cold, high-altitude ground cools by radiation. The air increases in density, and flows downhill. It can pick up speed, causing gale-force winds.
- The stormy conditions that lofted the dust on July 8 also brought wind, rain, and snow leading to the closure of at least two airports, Chile's Teletrece news site reported.
Figure 64: On July 8, 2016, the MODIS instrument on Terra acquired this natural-color image of an airborne dust cloud off the coast of Chile (image credit: NASA Earth Observatory, Jeff Schmalz)
• May 18, 2016: April in Greenland is typically very cold, though some years buck the trend. In 2012, for example, the surface of the ice sheet started melting early and then experienced the most extensive melting since the start of the satellite record in 1978. Weather events and temperature anomalies this April suggest that 2016 may be off to a similar start.
- The temperature anomaly map of Figure 65 is based on data from MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite. Observed by satellites uniformly around the world, LSTs (Land Surface Temperatures) are not the same as air temperatures. Instead, they reflect the heating of the surface by sunlight, and they can sometimes be significantly hotter or cooler than air temperatures.
- "The most remarkable aspect here is the incredible departure from 2001-2010 average, especially deep in the ice sheet interior," said Santiago de la Peña, a research scientist at Ohio State University. "This is accentuated by the fact that the northern regions of the United States and Canada actually experienced cooler than usual temperatures." According to de la Peña, a high-pressure weather system sat over the ice sheet through most of April. The system caused temperatures across Greenland to spike, reaching or matching record temperatures in many places. "There have been occasional warming events in the past during spring over Greenland," he noted, "but they affected only local areas and were not as intense."
- Still, warming events in Greenland are not entirely without precedent. Research by Dorothy Hall, an emeritus scientist at NASA's Goddard Space Flight Center, has shown that major melt events like those in 2012 and 2002 are not uncommon.
- De la Peña thinks such events will become more common in the future as atmospheric warming in the Arctic brings about longer melt seasons. For now, he notes that it is still early to predict how the melt season in 2016 will unfold. "High temperatures are still being recorded in May, suggesting we will have major melt events during the summer."
Figure 65: The MODIS map of Terra shows land surface temperatures for April 2016 compared to the 2001–2010 average for the same month. Red areas were hotter than the long-term average; some areas were as much as 20º Celsius warmer. Blue areas were below average, and white pixels had normal temperatures. Gray pixels were areas without enough data, most likely due to excessive cloud cover (image credit: NASA Earth Observatory, image by Jesse Allen)
• May 7, 2016: In early May 2016, a destructive wildfire burned through Canada's Fort McMurray in the Northern Alberta region. Windy, dry, and unseasonably hot conditions all set the stage for the fire. Winds gusted over 32 km/hour, fanning the flames in an area where rainfall totals have been well below normal in 2016. Ground-based measurements showed that the temperature soared to 32º Celsius on May 3 as the fire spread. 54)
- Observed by satellites uniformly around the world, LSTs (Land Surface Temperatures) are not the same as air temperatures. Instead, they reflect the heating of the land surface by sunlight, and they can sometimes be significantly hotter or cooler than air temperatures (Figure 66). The intense heat coincided with a weather pattern called an omega block. A large area of high pressure stalled the usual progression of storms from west to east. In Alberta, that left sinking, hot air parked over the region while the block was in place. But even before the omega block emerged, seasonal data show that winter in Alberta was warmer than usual.
- According to Robert Field, a Columbia University scientist based at NASA's Goddard Institute for Space Studies, El Niño likely played a role in the warmth. The Virginia Hills fire in central Alberta (May 1998) burned under a similar El Niño phase. "That fire occurred under comparable fire danger conditions, part of which you can trace to El Niño," Field said.
Figure 66: The temperature anomaly map is based on data from the MODIS instrument on the Terra satellite. The map shows the LST (Land Surface Temperature) from April 26 to May 3, 2016, compared to the 2000–2010 average for the same one-week period. Red areas were hotter than the long-term average; blue areas were below average. White pixels had normal temperatures, and gray pixels did not have enough data, most likely due to cloud cover (image credit: NASA Earth Observatory, image by Jesse Allen)
- The image of Figure 67 shows Fort McMurray on May 4, 2016, acquired by the Enhanced Thematic Mapper Plus (ETM+) on the Landsat-7 satellite. This false-color image combines shortwave infrared, near infrared, and green light (bands 5-4-2). Near- and short-wave infrared help penetrate clouds and smoke to reveal the hot spots associated with active fires, which appear red. Smoke appears white and burned areas appear brown. On this day the fire spanned about 100 km2; by the morning of May 5, it spanned about 850 km2 (Ref. 54).
Figure 67: ETM+ image of Landsat-7 of the Fort McMurray fire, acquired on May 4, 2016. Also visible in the Landsat image is the fire's complex pattern, with many active fronts (image credit: NASA Earth Observatory, image by Jesse Allen)
• May 4, 2016: April in Southeast Asia is usually a hot month, following the cool, dry season and preceding the monsoon season. But April 2016 was not your typical April. Throughout the month, ground-based measurements of air temperatures soared above average; one location in Thailand even broke the national record. 55)
- Satellite observations show a similarly hot picture. The map of Figure 68 shows land surface temperatures from April 2016 compared to the 2000–2012 average for the same month. Red areas were hotter than the long-term average by as much as 12º Celsius in some places; blue areas were below average. White pixels had normal temperatures, and gray pixels did not have enough data, most likely due to excessive cloud cover.
- According to news reports, at least 50 towns and cities matched or broke their daily air temperature records. On April 28, the temperature in Mae Hong Son was the highest ever recorded in Thailand, reaching 44.6 º Celsius.
- Southeast Asia was not the only area that endured intense heat in April. In India, ground-based measurements recorded temperatures 4-5º Celsius above normal. At least 300 people are reported to have died from heat-related complications during the month. A year earlier, more than 2,500 people died during India's 2015 heat wave—one of the five deadliest on record.
Figure 68: This temperature anomaly map is based on data from the MODIS instrument on NASA's Terra satellite, acquired in April 2016 (image credit: NASA Earth Observatory, image by Jesse Allen)
Legend to Figure 68: Observed by satellites uniformly around the world, land surface temperatures (LSTs) are not the same as air temperatures. Instead, they reflect the heating of the land surface by sunlight, and they can sometimes be significantly hotter or cooler than air temperatures.
• April 18, 2016: Long-term cloud cover study of MODIS data on Terra and on Aqua reveals species habitat. Much of Earth's biodiversity is concentrated in areas where not enough is known about species habitats and their wider distributions, making management and conservation a challenge. To address the problem, scientists at the University at Buffalo and Yale University used NASA satellite data to study cloud cover, which they found can help identify the size and location of important animal and plant habitats. 56) 57)
- Clouds influence such environmental factors as rain, sunlight, surface temperature and leaf wetness-all of which dictate where plants and animals can survive. As part of their study, researchers examined 15 years of data from NASA's Earth-orbiting Terra and Aqua satellites and built a database containing two images per day of cloud cover for nearly every square kilometer of the planet from 2000 to 2014. The study found that variations in cloud cover sharply delineated the boundaries of ecological biomes relevant to many unique species. 58)
- Advanced spatial assessment and monitoring of biodiversity in today's rapidly changing world is vital for managing future biological resources and a key element of several 2020 targets of the Convention on Biological Diversity and the Intergovernmental Platform on Biodiversity and Ecosystem Services. Growing evidence highlights the importance of fine-grain (≤1 km) climatic and environmental variability in driving the spatial distribution and abundance of organisms and the need to correctly capture this variation globally. Ecological research at regional to global extents remains reliant on environmental information that lacks important detail and is often interpolated between ground stations over vast distances of highly variable terrain.
- Cloud cover influences processes ranging from reproductive success in reptiles to leaf wetness, CO2 uptake, and the geographic distribution of plants. Especially in the tropics, seasonal variability of cloud cover is typically more important than day length and solar angle in reducing available solar irradiance, with multi-fold ecological consequences. These effects are difficult to observe in other remotely sensed products including vegetation indices, which for many parts of the world do not show much change throughout the year.
- The new 1 km dataset confirms equatorial South America, the Congo River basin in Africa, and Southeast Asia as the cloudiest regions of the world, with annual cloud frequencies (proportion of days with a positive cloud flag) ≥80% (Figure 69A). But, in contrast to existing evidence (S1 Table), the new product captures the frequency of cloud cover at substantially increased spatial resolution. In many regions (often but not always mountainous), cloud cover varies starkly over very short distances (Figure 69C), revealing variability hidden in spatially aggregated cloud products currently used in ecosystem, biodiversity, and climate modeling that are >100–10,000 times coarser.
- Remotely sensed information has the potential to revolutionize our understanding of spatial ecoclimatological patterns and processes through direct capture of environmental variation at fine spatial grain and global extent. Here, we have shown how global cloud dynamics can be quantified in unprecedented spatial detail and that cloud-associated factors are significantly associated with the distribution of various aspects of biodiversity habitats over large spatial scales.
Figure 69: Global 1 km cloud metrics. A) Mean annual cloud frequency (%) over 2000–2014. B) Inter-annual variability in cloud frequency (mean of 12 monthly standard deviations). C) Spatial variability (standard deviation of mean annual cloud frequency within a one-degree, ~110 km, circular moving window). D) Intra-annual variability in cloud frequency (standard deviation of 12 monthly mean cloud frequencies). Grey indicates the (A) median global cloud frequency (51%) and (B,D) median inter-annual variability (11%), blues indicate areas with below-median values, and reds indicate areas with higher-than-median values. Data are available only for MODIS land tiles, resulting in missing data in black tiles over oceans (image credit: A. M. Wilson, W. Jetz)
Figure 70: Seasonal cloud concentration. A) Color key illustrating the distribution of global cloud seasonality and concentration. The hue indicates the month of peak cloudiness, while the saturation and value indicate the magnitude of the concentration ranging from 0 (black, all months are equally cloudy) to 100 (all clouds are observed in a single month). B) Global distribution of seasonal cloud concentration with two red boxes indicating the locations of panels C and D. Coastlines shown in white, areas with no data are dark grey. C) Regional plot of northern South America illustrating the transition from June–July–August to December–January–February cloudiness with little seasonality (dark colors) at high elevations. D) Regional plot of southern Africa illustrating the transition from the Mediterranean climate in the southwest to the summer rainfall region in the northeast. Note the incursions of summer clouds and associated rainfall (red colors) along the southern coast. In C) and D), red lines indicate ecoregion boundaries (image credit: A. M. Wilson, W. Jetz)
• April 13, 2016: Antarctica has shed two new, large icebergs into the Southern Ocean. The bergs are the result of a crack that had been spreading across the Nansen Ice Shelf. The progression of the crack was visible in a pair of satellite images acquired in December 2013 and 2015. Ryan Walker and Christine Dow, glaciologists at NASA/GSFC (Goddard Space Flight Center), flew along the crack in late 2015. It was clearly still attached. On April 6, 2016, with southern winter soon to set in, satellite imagery indicated that the cracking ice front was still holding on. 59)
- The Nansen Ice Shelf previously measured about 35 km across and 50 km long. For comparison, the Drygalski Ice Tongue just south of Nansen stretches 80 km into the sea. Of the two bergs shed from Nansen, only one is large enough to meet the size criteria for naming and tracking by the U.S. National Ice Center. This larger piece is named C33.
- But why did the crack finally give out? According to Walker, summer melting probably helped weaken and break up the shelf fragments and sea ice (the mélange) within the crack, which acted like glue to keep the bergs attached. Summer melt also could have helped the deeply fissured ice to break further, completing the crack across the shelf.
- Once broken off, the new icebergs would have been blown away from the shelf by the strong katabatic winds that blow out to sea. "Nansen usually has pretty strong katabatic winds," Walker said.
- Walker emphasized that this is routine iceberg calving—there are indications that similar events occurred there in the 1960s—and not a collapse of the ice shelf. Still, some scientists are concerned for a different reason; the icebergs are threatening scientific equipment in the area. Scientists at New Zealand's National Institute of Water and Atmospheric Research (NIWA) say the bergs are deep enough that they cold snag a mooring deployed in Terra Nova Bay. The mooring collects data on the effects of climate change on sea ice and ice shelves.
- "We won't know until we go back next summer whether it is still there. We could lose a whole year of data. If that happens it will leave a gap in our research and that's unfortunate," said oceanographer Mike Williams in a NIWA press release. "However, it is a risk we have to take. We could see the crack from satellite images but predicting when an ice shelf will calve is difficult. It could have happened any time in the next five years."
Figure 71: On April 7, 2016, in the last days before winter darkness, MODIS on Terra acquired this image as the bergs broke away. (image credit: NASA Earth Observatory,, image by Jesse Allen)
• As of April 1, 2016, all Earth imagery from the Japanese ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) instrument aboard NASA's Terra spacecraft since late 1999, is now available to users everywhere at no cost. The public will have unlimited access to the complete 16-plus-year database for Japan's ASTER instrument of METI (Ministry of Economy, Trade and Industry), which images Earth to map and monitor the changing surface of our planet. ASTER's database currently consists of more than 2.95 million individual scenes. The content ranges from massive scars across the Oklahoma landscape from an EF-5 tornado and the devastating aftermath of flooding in Pakistan, to volcanic eruptions in Iceland and wildfires in California. 60)
- Previously, users could access ASTER's global digital topographic maps of Earth online at no cost, but paid METI a nominal fee to order other ASTER data products. In announcing the change in policy, METI and NASA cited ASTER's longevity and continued strong environmental monitoring capabilities. Launched in 1999, ASTER has far exceeded its five-year design life and will continue to operate for the foreseeable future as part of the suite of five Earth-observing instruments on Terra.
- The broad spectral coverage and high spectral resolution of ASTER provide scientists in numerous disciplines with critical information for surface mapping and monitoring of dynamic conditions and changes over time. Example applications include monitoring glacial advances and retreats, monitoring potentially active volcanoes, identifying crop stress, determining cloud morphology and physical properties, evaluating wetlands, monitoring thermal pollution, monitoring coral reef degradation, mapping surface temperatures of soils and geology, and measuring surface heat balance.
Figure 72: In Dec. 2015, one of Nicaragua's largest volcanoes, Momotombo, erupted for the first time since 1905. Continued activity at the end of February and into March 2016 produced large ash columns and pyroclastic (superheated ash-and-block) flows. On March 2, 2016, ASTER captured the volcano's eruptive activity during the day with its visible bands, and the previous night with its thermal infrared bands. The composite image shows a large blue-gray ash cloud covering the volcano's summit. The superimposed night data show the hot flows (in yellow) on the northeast flank, and the active summit crater in white. The data cover an area of 17 km x 18 km, located at 12.7º north, 86.6º west. 61)
Legend to Figure 72: With its 14 spectral bands from the visible to the thermal infrared wavelength region and its high spatial resolution of 15 to 90 m, ASTER images Earth to map and monitor the changing surface of our planet. ASTER is one of five Earth-observing instruments launched Dec. 18, 1999, on Terra. The instrument was built by Japan's Ministry of Economy, Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and data products.
• In March 2016, the Southern United States received a remarkable amount of precipitation. In the days after the slow-moving weather system cleared out, flood waters rose across several major river basins. 62)
- On March 14, 2016, the MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite captured an image of flooding in the vicinity of the Mississippi and White rivers. The image of Figure 73 is false color, composed from a combination of infrared and visible light (MODIS bands 7-2-1). Flood water appears dark blue; saturated soil is light blue; vegetation is bright green; and bare ground is brown. This band combination makes it easier to see flood water.
- The flooding was the result of an unusually strong low-pressure system that pulled in atmospheric moisture from both the Western Caribbean and the Eastern Pacific, according to meteorologists at Weather Underground. The system stalled over the southern states, and rainfall totals amounted to what would be expected to occur once every 200 years.
- The map of Figure 74 shows NASA's satellite-based estimates of rainfall over the Southern United States and the Gulf of Mexico from March 7–14. The brightest shades represent rainfall totals approaching 600 mm (24 inches) over the span of a week. The rainfall data represented in the map come from IMERG (Integrated Multi-Satellite Retrievals for GPM), a product of the GPM (Global Precipitation Measurement) mission. These regional, remotely sensed estimates may differ from the totals measured by ground-based weather stations.
- According to news reports, rain and flooding in the United States affected communities in Texas, Oklahoma, Arkansas, Louisiana, Mississippi, Tennessee, Alabama, and Kentucky. In Louisiana alone, the flooding was reported to have killed four people and damaged at least 5,000 homes.
Figure 73: Extend of flooding observed by the MODIS instrument on Terra [image credit: NASA Earth Observatory, using data from LANCE (Land Atmosphere Near real-time Capability for EOS), Jesse Allen]
Figure 74: IMERG data image of the GPM mission showing the total rainfall and the extend of the rainfall region in the US (image credit: NASA Earth Observatory, Joshua Stevens)
• Feb. 17, 2016: Two kinds of wave patterns are visible in the natural-color image of Figure 75, observed by MODIS on NASA's Terra satellite off the coast of Western Australia. Well offshore to the north and west, atmospheric waves are made visible by parallel bands of white clouds. Closer to the coast, the bright area of water is sunglint—the reflection of sunlight directly back toward the satellite imager. That sunglint makes it possible to see the faint ripples of internal waves; that is, large waves that propagate below the water surface, within the depths of the sea. 63)
- Waves form in the atmosphere for a variety of reasons. Sometimes the movement of an air mass over a bumpy feature—a mountain ridge, a volcano, or an island amidst a flat sea—will force air to rise or sink, creating ripples in the sky like those propagating across the surface of a pond. Other times, the collision of different air masses will cause a rippling effect.
- It is unclear what caused the atmospheric waves in the image of Figure75 . Off the west coast of Africa, we often see waves form when the dry air from the Sahara moves out over the much moister air over the tropical Atlantic Ocean. The dry air tends to push the moist air higher in the atmosphere, causing water vapor to form droplets and amass into clouds. The moist air rises, then gravity pulls it back down; the warm air rises again, then falls again. A series of cloud ripples mark the edges of the wave front as it propagates and dissipates.
- It is also possible—though perhaps less likely because of the distance—that the wave patterns in the image above have their origin inland. Western Australia is mostly desert and relatively flat, so it is possible that an atmospheric wave pattern formed when an air mass rode up over the Hamersley Range (just outside the scene) and out toward the sea.
- Internal waves are quirky phenomena that were scarcely known to science until the satellite era. They can be hundreds of meters tall and tens to hundreds of kilometers long. Enhanced by sunglint in the image above, these long wave forms moving across the sea surface are a visible manifestation of slow waves moving tens to hundreds of meters beneath the sea surface.
- Internal waves form because the ocean is layered. Deep water is cold, dense, and salty, while shallower water is relatively warmer, lighter, and fresher. The differences in density and salinity cause layers of the ocean to behave like different fluids. When tides, currents, and other large-scale effects of Earth's rotation and gravity drag water masses over some seafloor formations, it creates wave actions within the sea that are similar to those happening in the atmosphere.
- If you were on a boat, you would not necessarily see or feel internal waves because they are not expressed at the surface in different wave heights. Instead, they show up as smoother and rougher water surfaces that are visible from airplanes and satellites. As internal waves move through the deep ocean, the lighter water above flows up and down the crests and troughs. Surface water bunches up over the troughs and stretches over the crests, creating alternating lines of calm water at the crests and rough water at the troughs. Calm, smooth waters reflect more light directly back to the satellite, resulting in a bright, pale stripe along the length of the internal wave. The rough waters in the trough scatter light in all directions, forming a dark line.
- "There are definitely ocean internal waves in this image," said environmental engineer Nicole Jones of The University of Western Australia. "We have measured them off the coast of Ningaloo with instruments in the water. The different directions of the wave fronts are most likely due to the different seafloor slope directions in this region." She notes that internal waves play an important role in global ocean circulation and mixing, which is critical to understanding the ocean's role in climate and in the movement of nutrients and carbon from the depths to the surface and back. Jones and colleagues also study internal waves for their potential impact on drill rigs and other offshore structures.
Figure 75: On Feb. 10, 2016 (3:05 UTC), the MODIS instrument on Terra acquired this natural-color image of wave patterns off the coast of Western Australia (image credit: NASA Earth Observatory, Jeff Schmalz)
• February 3, 2016: Starting in early October 2015, farmers in southern Africa typically plant maize (corn)—an important food staple—across millions of hectares of land. But the first half of the 2015-2016 growing season was far from typical. Hot and dry conditions associated with a strong El Niño left experts wondering if a record agricultural drought was in the works. 64)
- Whether the season breaks a record won't be known until the growing season concludes in April 2016. But early in the season, when crops are normally planted, many areas saw inadequate growing conditions. According to Curt Reynolds of the USDA Foreign Agricultural Service, rainfall in South Africa's croplands from October through December 2015 was the lowest measured since at least 1981. With so little rainfall, sowing was delayed and plants could not emerge.
- Reynolds and others track growing conditions around the world by analyzing the NDVI (Normalized Difference Vegetation Index), a measure of how much plants absorb visible light and reflect infrared light. Drought-stressed vegetation reflects more visible light and less infrared light than healthy vegetation.
- This NDVI anomaly map above is based on data from the MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite. The map contrasts plant health in December 2015 against the 2000–2015 average for that month. Brown areas show where plant growth, or "greenness," was below normal. Greens indicate vegetation that is more widespread or abundant than normal for the time of year. Grays depict areas where data were not available, usually due to cloud cover.
- Three South African provinces—Free State, North West, and Mpumalanga—normally account for more than 80 percent of the country's maize/corn production. By January 24, 2016, Free State and North West still lacked green vegetation. Some greenery was visible in Mpumalanga, but the below-average levels hinted that crop yields would likely be low.
Figure 76: Drought in Southern Africa, acquired with MODIS on Terra in December 2015 (image credit: NASA Earth Observatory, Jesse Allen, Joshua Stevens)
- Assaf Anyamba, a remote sensing scientist with the NASA Goddard Earth Sciences Technology Center, noted that some areas were hit particularly hard by the drought. Among them was Lejweleputswa, a district in northwest Free State. The graph of Figure 77 the map shows how the measure of NDVI in Lejweleputswa midway through the 2015-2016 season compares to previous seasons and the mean from 2001–2015 (dashed gray line).
Figure 77: This temperature anomaly map is based on data from MODIS on Terra, it shows land surface temperatures in Dec. 2015 compared to the 2000–2015 average for that month. Red colors depict areas that were hotter than the average; blue colors were colder than average. White pixels were normal, and gray pixels did not have enough data (image credit: NASA Earth Observatory, Jesse Allen, Joshua Stevens)
• December 18, 2016: As of today, the Terra mission is 16 years on orbit. During this time the Terra satellite orbited the Earth more than 80,000 times, equivalent to a distance of > 5.6 billion km. 65)
- While Terra is not being replaced, Terra scientists eagerly await the launch of the Sentinel-3 spacecraft of ESA ( European Space Agency), scheduled for launch in early Feb. 2016. Sentinel-3 carries the OLCI (Ocean Land Color Instrument), which is similar to MODIS on Terra and Sentinel-3 will also have a morning crossing time like Terra.
- As the Flagship Earth Observing Satellite, Terra was the first satellite to look at Earth system science, collecting multiple types of data dedicated to various areas of Earth science. Scientists are able to document relationships between Earth's systems and examine their connections. In addition, Terra data has many applications that help people everyday.
• Nov. 18, 2015: Winter storms can blanket Iceland almost entirely with snow. The relative warmth of summer and fall, however, exposes a spectacular, varied landscape. "The visible snow cover is typical for this time of the year, compared to conditions during the past 15-20 years," said Thorsteinn Thorsteinsson, a glaciologist at the Icelandic Meteorological Office. He noted, however, that compared to the reference period of 1961-1990, snow cover is "almost certainly" less than average in the highland and mountain regions above 400 m in elevation. 66)
- The melting of seasonal snow cover accentuates the boundaries of Iceland's permanent ice caps. The ice caps appear smooth and rounded in contrast with the snow-covered interior plateau or the snow-capped ridges along the glacier-carved coastline. All ice caps in Iceland have been retreating rapidly and losing volume since 1995. In October 2015, however, scientists from the Icelandic Met Office showed that the Hofsjökull ice cap, outlined in red (Figure 78), had gained mass according to their ground-based measurements.
- An ice cap that has gained more mass than it has lost is said to have a positive mass balance. The graph below the image shows the annual mass balance of Thjórsárjökull, one of the ice cap's three basins, since the start of measurements in 1989. Thjórsárjökull's mass balance in 2015 was positive for the first time since 1993.
- The ice cap's reversal in 2015 is due to abundant winter precipitation and cool summer temperatures, explained Thorsteinsson. In spring 2015, the thickness of winter snowfall on the ice cap's three basins ranged from 25 to 60 percent above the 1995-2014 average. In the summer, melting was limited because of cool northerly winds.
- The situation changed in the fall, as September and October were unusually warm. When temperatures rise, melt water flows into the island's numerous lakes and reservoirs. Hálslón reservoir, the long and narrow feature on the east side, holds glacial meltwater. Öskjuvatn crater lake, Hágöngulón reservoir, and Thórisvatn natural lake and reservoir also stand out because they are dark and surrounded by snow.
- But one of the more prominent dark features just south of Öskjuvatn, is not water at all. "At first sight, one might think that this is another highland lake," Thorsteinsson said. "But actually, it is a fresh lava field" from the Holuhraun eruption from August 2014 to February 2015. During the eruption, lava poured from fissures just north of the Vatnajökull ice cap and near the Bárðarbunga volcano. By January 2015, the Holuhraun lava field had spread across more than 84 km2 . False-color satellite imagery here and here make it even more apparent that Holuhraun is not a lake.
Figure 78: MODIS on Terra acquired this this natural-color view of the Nordic island nation on November 9, 2015 (image credit: NASA Earth Observatory, Joshua Stevens, Jeff Schmaltz)
Figure 79: Illustration of the Hofsjökull ice cap water levels in the timeframe 1989 to 2015 (image credit: NASA Earth Observatory)
• October 21, 2015: Sierra Nevada is a Spanish name that means "snowy mountain range." While the term "snowy" has generally been true for most of American history, the mountain range has seen far less snow accumulation in recent years. The depth and breadth of the seasonal snowpack in any given year depends on whether a winter is wet or dry. Wet winters tend to stack up a deep snowpack, while dry ones keep it shallow. These images show the snowpack on the Sierra Nevada amid the wet year of 2011 (Figure 80) and the dry year of 2015 (Figure 81). They were acquired by MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite. 67)
- Both images were acquired on March 31, about halfway through the water year. A "water year" is the 12-month period from October 1 through September 30. The snowpack on the Sierra Nevada has generally peaked and begins to melt by the beginning of April. Meltwater runoff from that snowpack helps replenish rivers and reservoirs while recharging the groundwater.
- The wet year of 2011 buffered the initial effects of drought that returned in 2012, but dry conditions deepened in subsequent years. By March 2015, about one-third of the ground-based monitoring sites in the Sierra Nevada recorded the lowest snowpack ever measured. Some sites reported no snow for the first time. One month later, only some sites—generally those at higher elevations—had any measureable snowpack.
- Scientists from the University of Arizona wrote in a September 2015 article in Nature Climate Change, that the low snowpack conditions of 2015 were truly extraordinary. Tree-ring records of precipitation anomalies and of temperature allowed them to reconstruct a 500-year history of snow water equivalent in the Sierra Nevada. The researchers found that the low snowpack of April 2015 was "unprecedented in the context of the past 500 years." 68)
Figure 80: The snowpack on the Sierra Nevada amid the wet year of 2011, acquired by the MODIS instrument on Terra on March 31, 2011 (image credit: NASA, Earth Observatory, Jesse Allen)
Figure 81: The snowpack on the Sierra Nevada amid the dry year of 2015, acquired by the MODIS instrument on Terra on March 31, 2015 (image credit: NASA, Earth Observatory, jesse Allen)
• June 22, 2015: The NASA Science Senior Review Panel expects the Terra mission continuation through 2022, based on battery and fuel. Terra's long term data record is invaluable for teasing out subtle climate signals, including Earth's radiation budget, cloud properties, GPP (Gross Primary Productivity), Suomi-NPP, air pollution, radiative forcing, atmospheric composition, and aerosols. No spacecraft or instrument trends indicate that a major component is predicted to fail in the next 5 years. Normal on-orbit degradation is not expected to significantly limit the lifetime of any major spacecraft subsystem or component on-board within the next 5 years. 69)
- The Panel identified two Major Strengths, no Major Weaknesses, two Minor Strengths, and three Minor Weaknesses. The five instruments on Terra have continued to perform very well, which provides confidence that they will continue to perform at their current level through the proposed mission extension period. The propulsion, power, attitude determination and control, and primary communication systems continue to perform very well, maintain redundancies, and appear able to support science operations during the proposed mission extension period. - End of life planning is supported by a flight dynamics analysis that is well formulated with respect to constellation safety. The Terra mission benefits from ongoing efforts to modernize and improve ground systems, including multi-mission support modernization, operational scheduling, and IT security. However, overall data storage has been reduced by 17.2% due to the disabling of 10 of the total 58 PWA (Printed Wire Assembly) boards in the two spacecraft DMUs (Data Memory Units), thus reducing ASTER data collection significantly. The Terra batteries have two minor aging issues. The risk for the 4-year mission extension is expected to be higher.
- The Terra mission is now beyond 15 years of continuous data collection, providing fundamental observations of the Earth's Climate System, high-impact events, and adding value to other satellite missions and field campaigns. With 5 sensors providing a unique combination of spatial resolutions, temporal sampling, and multiple look angles, Terra is an exemplary mission that offers a tremendous long term data record capable of identifying subtle climate signals. The Terra mission is an international mission (US, Japan, and Canada) with broad participation among three NASA centers (JPL, Langley, and Goddard). The 5 sensors onboard Terra (ASTER, CERES, MISR, MODIS, and MOPPITT) collectively contribute to 81 calibrated and validated core data products. The value of Terra to the science and operational communities is unequivocal. The data distribution numbers for 2013 and 2014 exceed the combined distribution numbers for all other years combined – an indication of the continued and growing use of the data products. There were over 1,600 peer-reviewed papers in 2014, bringing the mission total to over 11,000. All of Terra's instruments are performing in exemplary fashion, except for ASTER's SWIR bands which were declared inoperable in 2009. Despite this, ASTER data have been used to produce 30 million tiles of the Global Digital Elevation Model -the most complete, consistent, high-resolution global topographic data set ever released.
• June 7, 2015: Looking up at the sky to enjoy the diversity and beauty of clouds is a pastime as ancient as humanity itself. Yet only during the past century—thanks to the Wright brothers and other pioneering aviators—have we had the ability to look down on clouds from above. 70)
- While a top-down view of clouds has led to important advances in meteorology and atmospheric science, it has also produced something much more difficult to quantify—simple beauty. For instance, on May 20, 2015, the MODIS (Moderate Resolution Imaging Spectroradiometer) instrument on NASA's Terra satellite captured this view of several cloud vortices swirling downwind of the Canary Islands and Madeira.
- Theodore von Kármán, a Hungarian-American physicist (1881-1963), was the first to describe the physical processes that create long chains of spiral eddies like the ones shown in Figure 82. Known as von Kármán vortices, the patterns can form nearly anywhere when fluid flow is disturbed by an object. In this case, the unique flow occurs as winds rush past the tall peaks on the volcanic islands. As winds are diverted around these high areas, the disturbance in the flow propagates downstream in the form of vortices that alternate their direction of rotation.
- Satellite sensors have spotted von Kármán vortices around the globe before, including off of Guadalupe Island, near the coast of Chile, in the Greenland Sea, in the Arctic, and even next to a tropical storm. However, this scene is particularly notable for the fact that three distinct streams of vortices are visible.
Figure 82: Von Kármán vortices over the northwest coast of Africa, acquired on May 20, 2015 with MODIS on Terra (image credit: NASA Earth Observatory, Jeff Schmaltz)
•June 5, 2015: May is generally the hottest month in India, but even by local standards May 2015 was unusual. For nearly two weeks, many areas faced temperatures that were 5.5º C above normal. By June 4, the extreme weather had claimed the lives of more than 2,500 people, according to news reports. That put the heat wave among the five deadliest on record. Many of the victims were elderly, homeless, or construction workers. 71)
- By observing outgoing longwave radiation, the CERES (Clouds and Earth's Radiant Energy System) sensor on NASA's Terra satellite offers a different view of the intensity and breadth of the heat wave. Outgoing long wave radiation is a measure of the amount of energy emitted to space by Earth's surface, oceans, and atmosphere. The hotter an area is, the more energy it radiates. The false-color map (Figure 83) shows how much outgoing radiation left Earth's atmosphere between May 15 and May 27. The amount of heat energy radiated (in W/m2) is depicted in shades of purple. Light purple areas emitted the most longwave radiation and were the warmest. Darker purple areas emitted less radiation and were cooler.
- As observed by CERES, the hot weather was not limited to India. Pakistan, southern Iran, the United Arab Emirates, and Oman also faced extremely hot temperatures. On some days, it was even hotter in parts of Pakistan than it was in India, according to news reports. On June 3, temperatures soared to 50.7º Celsius in Sweihan, a town in the United Arab Emirates.
- Part of the reason the death toll has been so high in India is because of the humidity. Many of the deaths occurred in Andhra Pradesh and Telangana, states in southern India that faced extremely high humidity as well as extreme temperatures. High humidity increases the heat index and makes temperatures feel even warmer. Humidity plays a critical role in deadly heat waves because the human body relies on sweat to cool itself. If humidity gets too high, sweat cannot evaporate efficiently and the body begins to overheat.
Figure 83: This false-color map shows how much outgoing radiation left Earth's atmosphere between May 15-27, 2015 (image credit: NASA Earth Observatory image, Jesse Allen)
• June 4, 2015: The Nepal 7.8 magnitude Gorkha earthquake and its aftershocks. As millions of people regroup from earthquakes in Nepal, a team of international volunteers is combing through satellite imagery of the region to identify additional hazards: earthquake-induced landslides. "Landslides are a common secondary hazard triggered by earthquakes or rainfall," said Dalia Kirschbaum, a remote sensing scientist at NASA's Goddard Space Flight Center and a leader of a landslide mapping effort. "Because landslides can mobilize and move so quickly, they often cause more damage than people realize." 72)
Figure 84: Map of the Nepal Gorkha earthquake locations of landslide events and hazards acquired by instruments on various spacecraft (image credit: NASA Earth Observatory, Jesse Allen)
Legend to Figure 84: The colors represent the teams that found or are studying them. ICIMOD (red) stands for the International Centre for Integrated Mountain Development, an institution focused on improving the lives of people in the Hindu Kush Himalayan region. ICIMOD also serves as a regional hub for SERVIR, a joint initiative by NASA and the U.S. Agency for International Development. Both Kirschbaum and Kargel are members of NASA's SERVIR Applied Sciences team.
- As part of a disaster-relief response to the 7.8-magnitude Gorkha earthquake and its aftershocks, Kirschbaum and Jeff Kargel, a glaciologist at the University of Arizona, are organizing a group of volunteer scientists to identify where and when landslides have occurred in earthquake-affected areas of Nepal, China, and India. From April 25, the date of the first earthquake, to May 20, the team has collectively mapped nearly 1,000 landslides. Different subgroups have focused on disaster mapping, measurement and assessment, hazard impact, or communications. Some teams create damage proxy maps that tell the type and extent of the existing damage; others create vulnerability maps that show potential risks.
- Kargel helped form one landslide-mapping subgroup—the "induced hazards" team—in order to identify hazards triggered by the earthquakes and to help guide relief efforts. He found nearly 40 volunteers by reaching out to a NASA-supported network called Global Land Ice Measurements from Space (GLIMS). "It's stunning to see the level of commitment, passion, and forensic skill the volunteers are bringing to these tasks," said Kargel. "There are no words to describe this sense of mission that goes way above the scientific call of duty."
- Mapping landslides is especially important because of the impending monsoon season. The highest number of landslides occur during the rainy months between June and October, Kirschbaum noted. In general, if the land has slid in a specific area, it will have a higher likelihood of experiencing another landslide because the ground is unstable and more susceptible to environmental triggers like heavy rain. In the aftermath of the Gorkha earthquake, researchers are concerned that landslides will be even more frequent this year.
- The landslide mapping effort includes researchers from Nepal, the United States, Canada, the United Kingdom, China, Japan, Australia, and the Netherlands. The collaborators provided information that Nepalese government, military, and scientific entities could use to make informed decisions about evacuations and relief support. - The mapping effort will have a long-term benefit, as well. "How can we better understand landslide processes scientifically," Kirschbaum asked, "and then how can we use models, weather forecasts, and other tools to help government and science entities protect citizens?"
- The NASA-sponsored team is using satellite images to identify landslide locations, to characterize additional hazards (for example, dammed lakes), and to incorporate other useful information such as locations of nearby villages. Data sources include the Landsat satellites, the Earth Observing-1 satellite, the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) instrument on the Terra satellite, the WorldView and GeoEye satellites operated by Digital Globe, and image mosaics and topographic information accessible in Google Earth. As an example, Figure 85 is a natural-color view of the study area that was acquired by Landsat 8 on June 1, 2015.
- A U.K. mapping team (blue dots on the map) consists of scientists from the British Geological Survey (BGS) and Durham University. Like their NASA-sponsored colleagues, they are identifying landslides using satellite data from various sources and building a database for future study and for relief efforts.
- Researchers in Nagoya University (NGA; purple on the map) in Japan have identified more than 600 potential earthquake-induced landslides. An independent, Canadian-based group of MDA (MacDonald, Dettwiler and Associates Ltd.) has been locating landslides and potential landslides by analyzing areas before and after the earthquakes using data from RADARSAT-2 (orange-brown on the map), an Earth-observing satellite from the Canadian Space Agency.
Figure 85: Sample image of OLI on Landsat-8 acquired on June 1, 2015 (image credit: NASA Earth Observatory, Jesse Allen)
• June 2, 2015: Fourteen Years of Carbon Monoxide Measurements from MOPITT on Terra. Carbon monoxide is perhaps best known for the lethal effects it can have in homes with faulty appliances and poor ventilation. In the United States, the colorless, odorless gas kills about 430 people each year. However, the importance of carbon monoxide (CO) extends well beyond the indoor environment. Indoors or outdoors, the gas can disrupt the transport of oxygen by the blood, leading to heart and health problems. CO also contributes to the formation of tropospheric ozone, another air pollutant with unhealthy effects. And though carbon monoxide does not cause climate change directly, its presence affects the abundance of greenhouse gases such as methane and carbon dioxide. 73)
- Carbon monoxide forms whenever carbon-based fuels — including coal, oil, natural gas, and wood — are burned. As a result, many human activities and inventions emit carbon monoxide, including: the combustion engines in cars, trucks, planes, ships, and other vehicles; the fires lit by farmers to clear forests or fields; and industrial processes that involve the combustion of fossil fuels. In addition, wildfires and volcanoes are natural sources of the gas.
- Little was known about the global distribution of carbon monoxide until the launch of the Terra satellite in 1999. Terra carries a sensor MOPITT (Measurements of Pollution in the Troposphere) that can measure carbon monoxide in a consistent fashion on a global scale. With a swath width of 640 km, MOPITT scans the entire atmosphere of Earth every three days.
- Since CO has a lifetime in the troposphere of about one month, it persists long enough to be transported long distances by winds, but not long enough to mix evenly throughout the atmosphere. As a result, MOPITT's maps show significant geographic variability and seasonality. To view month by month maps of carbon monoxide, visit the carbon monoxide page in Earth Observatory's global maps section.
- In Africa, for example, agricultural burning shifts north and south of the equator with the seasons, leading to seasonal shifts in carbon monoxide. Fires are also the dominant source of carbon monoxide pollution in South America and Australia. In the United States, Europe, and eastern Asia, the highest carbon monoxide concentrations occur around urban areas and tend to be a result of vehicle and industrial emissions. However, wildfires burning over large areas in North America, Russia, and China also can be an important source.
- Terra has been in orbit long enough to observe significant changes over time. To illustrate how global carbon monoxide concentrations have changed, maps of the mission's first (2000) and most recent full year (2014) of data are shown in Figure 86. The maps depict yearly average concentrations of tropospheric carbon monoxide at an altitude of 3,700 meters (12,000 feet). Concentrations are expressed in parts per billion by volume (ppbv). A concentration of 1 ppbv means that for every billion molecules of gas in a measured volume, one of them is a carbon monoxide molecule. Yellow areas have little or no carbon monoxide, while progressively higher concentrations are shown in orange and red. Places where data was not available are gray. For both years, the data has been averaged, which eliminates seasonal variations.
- According to MOPITT, carbon monoxide concentrations have declined since 2000 (Figure 86). The decrease is particularly noticeable in the Northern Hemisphere. Most air quality experts attribute the decline to technological and regulatory innovations that mean vehicles and industries are polluting less than they once did. Interestingly, while MOPITT observed slight decreases of carbon monoxide over China and India, satellites and emissions inventories have shown that other pollutants like sulfur dioxide and nitrogen dioxide have risen during the same period.
- "For China, nitrogen dioxide emissions are mostly from the power and transportation sectors and have grown significantly since 2000 with the increase in demand for electricity," explained Helen Worden, an atmospheric scientist from the National Center for Atmospheric Research (NCAR). "Carbon monoxide emissions, however, have a relatively small contribution (less than 2 percent) from the power sector, so vehicle emissions standards and improved combustion efficiency for newer cars have lowered carbon monoxide in the atmosphere despite the fact that there are more vehicles on the road burning more fossil fuel."
- As illustrated by the maps, the news is also generally positive for the Southern Hemisphere, where deforestation and agricultural fires are the primary source of carbon monoxide. In South America, MOPITT observed a slight decrease in carbon monoxide; other satellites have observed decreases in the number of small fires and areas burned, suggesting a decrease in deforestation fires since 2005. Likewise, MOPITT has observed decreases in the amount of carbon monoxide over Africa. "There have been fewer fires in Africa, so that is a big part of the story there," explained Worden. "However, growing cities might be increasing of the amount of CO in some areas of equatorial Africa."
- The line graph of Figure 87 shows the long-term trend as well as monthly variations in carbon monoxide concentrations. While the overall trend is downward, several peaks and valleys are visible. For instance, some researchers attribute the peak from around 2002 to 2003 to an unusually active fire season in the boreal forests of Russia. The dip in carbon monoxide emissions from 2007 to 2009 also matches a decline in global fire emissions. In addition, researchers have noted that this dip overlaps with a global financial crisis that started in late 2008 and caused global manufacturing output to decline.
Figure 86: Earth's CO concentration acquired with MOPITT on Terra in 2000 (top) and in 2014 (bottom), image credit: NASA Earth Observatory, Jesse Allen and Joshua Stevens
Figure 87: Long-term CO concentration trend and monthly variations as measured by MOPITT (image credit: NASA Earth Observatory, Jesse Allen and Joshua Stevens)
• On April 22, 2015, the Calbuco volcano in southern Chile began erupting for the first time since 1972. An ash cloud rose at least 15 km above the volcano (Figure 88), menacing the nearby communities of Puerto Montt (Chile) and San Carlos de Bariloche (Argentina). The eruption led the Chilean Emergency Management Agency and the Chilean Geology and Mining Service (SERNAGEOMIN) to order evacuations within a 20 km radius around the volcano. About 1,500 to 2,000 people were evacuated; no casualties have been reported so far. 74)
Figure 88: At 14:20 UTC on April 23, 2015, the MODIS instrument on the Terra satellite acquired a natural-color image of the extensive ash plume (image credit: NASA Earth Observatory, Joshua Stevens, Jeff Schmalz)
• In Feb. 2015, the Terra spacecraft and its payload continue to provide key data to address the interrelationships between Earth's various systems, long after its planned lifetime. With only one minor glitch, those data continue to be obtained and disseminated to a wide range of communities, giving further testimony to the excellence of those far-sighted individuals and organizations responsible for Terra and its increasingly large family of LEO (Low Earth Orbit) remote-sensing instruments. 75)
- On Dec. 18, 2014 the Terra spacecraft was 15 years on orbit. Terra is still operating at near-full capability, now nine years beyond its designed six year lifetime, with only slight reductions in its data-gathering capabilities. The Terra mission has enabled new discoveries in Earth System Science. Dedicated engineers and scientists work together to calibrate instruments, process and store the vast quantities of data returned, validate results, and continue to coax cutting edge science out of aging hardware.
• Dec. 10, 2014: The mountains surrounding Kashmir Valley now trap air a bit like they once trapped water. The high ridges can set up airflow patterns that concentrate smoke and other airborne pollutants near the valley floor, causing outbreaks of haze (Figure 89). 76)
- Haze is most likely to occur when warm, buoyant air moves over cooler, denser air—a situation meteorologists call a temperature inversion. Temperature inversions often develop on winter nights as the surface loses heat and chills the air immediately above. Mountain valleys often strengthen inversions because cold air from mountaintops tends to flow down slopes and push warmer air up from the floor in the process. Snow cover also increases the likelihood of an inversion because snow cools the air near the surface by reflecting much of the Sun's energy rather than absorbing it. With a temperature inversion in place, air in the valley becomes stagnant; the warm air above it acts like a cap and prevents pollutants from dispersing.
- Much of the haze visible in the image likely had its origins in charcoal production or the burning of biomass. Charcoal is widely used to heat homes in the Kashmir Valley in the winter and emits several types of polluting gases and aerosol particles into the atmosphere.
Figure 89: Haze in the Kashmir Valley, acquired by MODIS on Terra on Dec. 5, 2014 (image credit: NASA, Jeff Schmalz)
Legend to Figure 89: About 4.5 million years ago, the Kashmir Valley was at the bottom of a large lake, encircled by a ring of rugged mountains. Much of the lake's water has long since drained away through an outlet channel on the valley's west side. However, evidence of the lake remains in the bowl-like shape and the clay and sand deposits on the valley floor.
• May 21, 2014: Fires in Russia in May 2014 fueled pyrocumulus clouds that pumped smoke high into the atmosphere. With dozens of forest fires burning in Russia's Irkutsk region, authorities have declared a state of emergency (Figure 90). 77)
Some of the blazes likely began on farms but then spread into forests due to high winds and warm temperatures. As seen on Worldview, MODIS began to detect small fires in Irkutsk on May 14. Many were along rivers near farmland. After burning at a moderate level for a few days, the size and intensity of the fires increased significantly on May 18.
In addition to producing thick plumes of smoke, the fires fueled numerous pyrocumulus clouds—tall, cauliflower-shaped clouds that billowed up above the smoke. Pyrocumulus are similar to cumulus clouds, but the heat that forces the air to rise—which leads to cooling and condensation of water vapor—comes from fire instead of sun-warmed ground. In satellite images, pyrocumulus clouds appear as opaque white patches hovering over darker smoke.
Figure 90: The MODIS instrument on Terra captured this image on May 18, 2014 (image credit: NASA Earth Observatory)
Legend to Figure 90: The red outlines indicate hot spots where MODIS detected unusually warm surface temperatures associated with fires. The image is centered at 56.76º North and 105.47º East.
• The Terra spacecraft and its sensor complement (except the SWIR bands on ASTER) are operating nominally in 2014.
Legend of Figure 91: The remarkably cloud-free view shows the range of ecological diversity present on the island. Many of the world's climate zones can be found on Hawaii for two related reasons: rainfall and altitude. The Big Island is home to Mauna Kea, the tallest sea mountain in the world at 4,205 m and the tallest mountain on the planet—if you measure from seafloor to summit, a distance of more than 9,800 m.
Despite Mauna Kea's height, it is Mauna Loa that dominates the island. With an altitude of about 4,169 m — the actual number varies depending on volcanic activity — Mauna Loa is the most massive mountain in the world. Temperatures dip low at the summit of these peaks, resulting in a tree-free polar tundra, pale brown in this image.
The mountains help shape rainfall patterns on Hawaii so that desert landscapes exist side-by-side with rainforests. In fact, average yearly rainfall ranges from 204 mm to 10,271 mm . Trade winds blow mostly from the east-northeast, and the sea-level breezes hit the mountains and get forced up, forming rainclouds. The east side of the island is lush and green with tropical rainforest. Much less moisture makes it to the lee side of the mountains. The northwestern shores of Hawaii are desert. Kona, on the western shore, receives plenty of rain because the trade winds curve back around the mountains and bring rain. Pale green areas on all sides of the island are agricultural land and grassland.
The other environmental force painting Hawaii's canvas is volcanism. Mauna Loa and Mauna Kea are both volcanic, though only Mauna Loa has been active recently. However, in this department, Kilauea is the superlative: It is one of the world's most active volcanoes. A small puff of steam rises from an erupting vent in this image. Black and dark brown lava flows extend from both Kilauea and Mauna Loa.
• January 2014: A swirling mass of Arctic air moved south into the continental United States in early January 2014. On January 3, the air mass began breaking off from the polar vortex, a semi-permanent low-pressure system with a center around Canada's Baffin Island. The frigid air was pushed south into the Great Lakes region by the jet stream, bringing abnormally cold temperatures to many parts of Canada and the central and eastern United States.
- When the cold air passed over the relatively warm waters of Lake Michigan and Lake Superior, the contrast in temperatures created a visual spectacle. As cold, dry air moved over the lakes, it mixed with warmer, moister air rising off the lake surfaces, transforming the water vapor into fog—a phenomenon known as steam fog. 79)
The result: One of the coldest Arctic outbreaks in two decades has plunged into the USA, bringing bitterly cold temperatures to the Midwest, South and East. 80)
Figure 92: Natural color image of MODIS on Terra captured on January 6, 2013 showing fog forming over the lakes and streaming southeast with the wind (image credit: NASA)
Figure 93: A false color image of MODIS on Terra acquired on January 6, 2014which helps to illustrate the difference between snow (bright orange), water clouds (white), and mixed clouds (peach), image credit: NASA
• December 01, 2013: Offshore from Argentina, spring is in bloom. Massive patches of floating phytoplankton colored the ocean in November 2013. These microscopic, plant-like organisms are the primary producers of the ocean, harnessing sunlight to nourish themselves and to become food for everything from zooplankton to fish to whales. 81)
Figure 94: The MODIS instrument on NASA's Terra satellite acquired this natural-color image on Nov. 26, 2013 (image credit: NASA)
Legend to Figure 94: The chalky blue swirls in the South Atlantic Ocean, as well as fainter streaks of yellow and green, are evidence of abundant growth of phytoplankton across hundreds of kilometers of the sea. These organisms contain pigments (such as chlorophyll) or minerals (calcium carbonate) that appear blue, green, white, or other colors depending on the species. The phytoplankton in this image are likely a blend of diatoms, dinoflagellates, and coccolithophores. Near the coast, the discoloration of the water could be phytoplankton or it might be sediment runoff from rivers.
These phytoplankton help fuel one of the world's best fishing grounds, particularly for shortfin squid, hake, anchovies, whiting, and sardines. The area known as the Patagonian "shelf-break front," is a crossroads of currents—Circumpolar, Brazil, and Malvinas—where nutrients are carried in from southern waters or churned up from the edge of the continental shelf.
• June 2013: The 2013 Senior Review evaluated 13 NASA satellite missions in extended operations: ACRIMSAT, Aqua, Aura, CALIPSO, CloudSat, EO-1, GRACE, Jason-1, OSTM, QuikSCAT, SORCE, Terra, and TRMM. The Senior Review was tasked with reviewing proposals submitted by each mission team for extended operations and funding for FY14-FY15, and FY16-FY17. Since CloudSat, GRACE, QuikSCAT and SORCE have shown evidence of aging issues, they received baseline funding for extension through 2015. 82)
- The Science Panel endorses the continuation of the Terra mission because it will extend the records for numerous data products used to monitor and understand changes in climate and the effects of those changes on land, ocean, and atmosphere over the next few years. The Terra mission has already accumulated 13 years of data from five instruments, each of which provides valuable data for scientific questions pertaining to the Earth and its changes, including 79 core products as well as support for monitoring and relief efforts for natural and man-made disasters. The continuation of the Terra mission would extend the baseline of these measurements and, for some instruments, provide continuity linking past and future missions.
- The products from Terra are invaluable to a large number of scientific investigations related to the Earth system and global change. From the perspective of the Science Panel, the data from MODIS, alone, justifies that the mission be continued.
• In June 2013, a wildfire broke out in Black Forest, a wooded suburb of Colorado Springs, CO, USA. The fire charred more than 5,700 hectare, destroying 509 homes and killing two people. The Black Forest fire was the most destructive in the state's history. 83)
Figure 95 provides an image of the burn scar on June 21, 2013. Vegetation-covered land is red in the false-color image, which includes both visible and infrared light. Patches of unburned forest are bright red. Unburned grasslands are pink. The darkest gray and black areas are the most severely burned. Buildings, roads, and other developed areas appear light gray and white.
The most severe damage occurred north of Shoup Road, but the severity varied widely by neighborhood. Cathedral Pines, for instance, escaped largely unscathed. Many residents of that neighborhood put rocks around their homes, removed vegetation and dead trees from their yards, avoided using mulch, and followed other fire prevention strategies that helped keep flames back long enough for fighters to save homes
One key building that escaped the flames was Edith Wolford elementary school. Though it was in the middle of an area that was severely burned, the school survived intact partly because of the large, treeless parking lot surrounding it.
Figure 95: Aftermath of Colorado's most destructive wildfire observed by the ASTER instrument on the Terra satellite on June 21, 2013 (image credit: NASA)
Figure 96: Play of light on water as observed by MODIS, a result of sunglint (NASA, Jeff Schmaltz LANCE/EOSDIS MODIS Rapid Response Team)
Legend to Figure 96: In the image, wavy, windsock-like tails stretch to the southwest from each of the islands. The patterns are likely the result of winds roughening or smoothing the water surface in different places. Prevailing winds in the area come from the northeast, and the rocky, volcanic islands create a sort of wind shadow—blocking, slowing, and redirecting the air flow. That wind, or lack of it, piles up waves and choppy water in some places and calms the surface in others, changing how light is reflected. Ocean currents, oil or pollution slicks, and internal waves can also alter surface patterns, though none are necessarily visible in this image.
• The Terra spacecraft and its sensor complement (except the SWIR bands on ASTER) are operating nominally in 2013. NASA extended the mission to 2015 (after the 2011 review). 85)
Figure 97: MODIS image of a dust storm that blew out of Libya and across the Mediterranean Sea in late March 2013 (image credit: NASA)
Legend to Figure 97: MODIS on NASA's Terra satellite acquired this natural-color image of the dust storm on March 30, 2013. The dust plumes arose hundreds of kilometers inland, and dust stretched across the Mediterranean Sea toward southern Italy. - Southwest of the coastal city of Banghazi (Benghazi), an especially thick dust plume spanned roughly 100 km , and the plume was thick enough to completely hide the ocean surface below. 86)
Figure 98: Air over Beijing China on January 14, 2013 as observed with the MODIS instrument (image credit: NASA, Jeff Schmaltz)
Legend to Figure 98: Residents of Beijing and many other cities in China were warned to stay inside in mid-January 2013 as the nation faced one of the worst periods of air quality in recent history. The Chinese government ordered factories to scale back emissions, while hospitals saw spikes of more than 20 to 30 % in patients complaining of respiratory issues, according to news reports. 87)
• The Terra spacecraft and its instruments are operating nominally in 2012 (> 12 years on orbit). - In June 2011, the NASA Earth Science Senior Review recommended an extension of the Terra mission as baseline up to 2013 and a further extension as baseline up to 2015.
Legend to Figure 99: Enriched by nutrients carried in by the Danube, Dnieper, Dniester, Don and other rivers, the waters of the Black Sea are fertile territory for the growth of phytoplankton. The bounty is a mixed blessing. The milky, light blue and turquoise-colored water in the middle of the sea is likely rich with blooming phytoplankton that trace the flow of water currents. Closer to the coast, the colors include more brown and green, perhaps a brew of sediment and organic matter washing out from rivers and streams, though it may also be a sign of phytoplankton. Puffs of spring clouds linger over parts of the coastline.
Figure 100: Natural color image of MODIS acquired on January 23, 2012 showing a winter storn in the Pacific Northwest (image credit: NASA)
• The Terra spacecraft and its instruments are operating nominally in 2011. Terra is a huge success, and continuation of the data collection 11 year TERRA record from the five instruments: ASTER, CERES, MISR, MODIS, MOPITT, is critical to a wide array of earth system science.
According to the NASA Earth Science Senior Review 2011, the Terra platform is expected to remain fully functional through 2017 (battery, fuel, subsystems performance). The main failure to date is the SWIR bands on ASTER. But there continues to be significant use of the ASTER data from optical and TIR bands, and from the new global DEM. 89)
Figure 101: Waves of dust dance off the African Coast - this MODIS natural color image was taken on Sept. 23,2011 (image credit: NASA)
Legend to Figure 101: The dust plumes sport a wave-like appearance—bands of thick dust alternating with bands of relatively clear air. Some waves extend westward while others curve toward the south in giant arcs. At the end of one curving wave of dust, a line of clouds extends southward over the sea. These ribbon-like patterns might result from atmospheric waves. - Sand seas sprawl over much of Mauritania, and the abundant sand provides plentiful material for dust storms. This dust storm hasn't yet reached Cape Verde, which lies to the southwest, but the dust appears headed in that general direction.
• More than a decade after launch, the Terra spacecraft and its instruments are operating nominally in 2010 (design life of six years). The spacecraft remains in extraordinary good condition and with enough fuel to provide its service for another 6-7 years to come. 90) 91) 92)
All five instruments onboard the spacecraft continue to gather scientific data, although one of the three telescopes on ASTER is no longer working. ASTER stopped capturing useful SWIR imagery in 2008. The spacecraft is still working on its primary spacecraft components with one exception - the DASM (Direct Access System Module) which broadcasts MODIS data to 150 sites around the world, experienced a failure in 2008. The mission team switched the broadcast services to the redundant module.
The MISR instrument has been collecting global Earth data from NASA's Terra satellite since February 2000. With its nine along-track view angles, four visible/near-infrared spectral bands, intrinsic spatial resolution of 275 m, and stable radiometric and geometric calibration, no instrument that combines MISR's attributes has previously flown in space. The more than 10-year (and counting) MISR data record provides unprecedented opportunities for characterizing long-term trends in aerosol, cloud, and surface properties, and includes 3-D textural information conventionally thought to be accessible only to active sensors. Technology development is underway to extend future multiangle measurements to broader spectral range (ultraviolet to thermal infrared), wider spatial swaths (enabling more rapid global coverage), and accurate polarimetric imaging. 93)
• In the summer 2010, the project is reporting that many lessons have been learned from MODIS instrument operation, calibration, performance, algorithm refinements, and calibration coefficient LUT (Look Up Tables) updates. Listed in the following are some important factors that need to be considered to assure sensor performance and data quality: 94) 95)
- Comprehensive pre-launch calibration and characterization
- Dedicated calibration and validation effort throughout entire mission
- Close interactions among science and calibration teams and input from users
- Complete documentation on instrument operation concept, sensor calibration ATBD (Algorithm Theoretical Basis Document), algorithm and LUT update procedures, and sensor performance.
MODIS lessons have provided and will continue to provide valuable information for future missions and sensors, such as the VIIRS on the NPP and JPSS, ABI on GOES-R, OLI and TIRS on LDCM, and CLARREO. — Since launch, both Terra and Aqua MODIS have provided an unprecedented amount of high quality data and made significant contributions to the studies of short- and longterm changes in the Earth's system.
• Terra spacecraft deep space calibration: In early 2003, the Terra S/C performed two deep space calibration maneuvers. The objective of the maneuvers is to provide the science instruments with calibration opportunities using the cold background of deep space and also the stable lunar surface as calibration targets. These maneuvers help to identify and to quantify payload data inaccuracies, such as scan-dependent offsets, allowing for the correction and for more accurate data products. Additionally, the lunar calibration maneuver enables inter-calibration with other spacecraft (e.g. SeaWiFS/SeaStar, Aqua MODIS) observing the same illumination reference.
A 240º pitch maneuver is designed to protect the instrument deck from sun exposure and also to provide a steady-state slew during the lunar viewing. The 35 minutes eclipse period and the requirements for a nearly perfect moon placement and continuous communications coverage impose a strict timing constraint on the execution of the maneuvers. The GN&C has to perform beyond the experience and constraints of a heritage system design. - When Terra executed the maneuvers, FDIR protection as well as the S/C attitude and instrument performance met or exceeded all expectations.
• MOPITT operational history: First data were collected in March 2000 and then almost continuously from March 22, 2000 until May 7, 2001 at which point the instrument was shut down due to an anomaly. However, data collection in reduced mode (less height resolution) was resumed on August 23, 2001 and has continued since then. It has produced a complete dataset of CO over the globe period of 14 months from March 2000 to May 2001 (reduced resolution data set after Aug. 2001). It has provided one of the first global dynamic pictures of tropospheric pollution and its transport on both the regional and global scale. Continued coverage will enable the science team to examine more aspects of the large-scale transport within the lower atmosphere.
An appropriately chosen redundancy scheme has extended the life of the instrument beyond the mission requirements. The success of the instrument can be attributed to its long life mechanisms, which continue to operate at high speeds. With the LMC motors currently exceeding 2 billion rotations, and the choppers over 5 billion rotations, the successful mechanism design has been proven on orbit. MOPITT has made upwards of 60 million measurements, and an application has been made to NASA to extend the Terra mission from nominally 6 years to 10 years, based on the success of MOPITT and the other instruments on the spacecraft (see Ref. 128).
• The commissioning phase of Terra (checkout and verification) lasted until Feb. 23, 2000 when the spacecraft reached also its final orbit. After this the observatory began its observations phase collecting scientific data.