Aqua Mission (EOS/PM-1)
The Aqua mission is a part of the NASA's international Earth Observing System (EOS). Aqua was formerly named EOS/PM-1, signifying its afternoon equatorial crossing time. NASA renamed the EOS/PM-1 satellite to Aqua on Oct. 18, 1999. The Aqua mission is part of NASA's ESE (Earth Science Enterprise) program. 1) 2) 3)
The focus of the Aqua mission is the multi-disciplinary study of the Earth's water cycle, including the interrelated processes (atmosphere, oceans, and land surface) and their relationship to Earth system changes. The data sets of Aqua provide information on cloud formation, precipitation, and radiative properties, air-sea fluxes of energy, carbon, and moisture (AIRS, AMSU, AMSR-E, HSB, CERES, MODIS); and sea ice concentrations and extents (AMSR-E).
Figure 1: Illustration of the Aqua satellite (image credit: NASA)
The Aqua spacecraft is based on TRW's modular, standardized AB1200 bus design (also referred to as T-330 platform) with common subsystems (Note: Northrop Grumman purchased TRW in Dec. 2002). The satellite dimensions are: 2.68 m x 2.47 m x 6.49 m (stowed) and 4.81 m x 16.70 m x 8.04 m (deployed). Aqua is three-axis stabilized, with a total mass of 2,934 kg at launch, S/C mass of 1,750 kg, payload mass =1,082 kg, propellant mass = 102 kg; power = 4.86 kW (EOL). Propulsion: hydrazine blow-down system; 4 pairs of thrusters. The design life is six years.
RF communications: X-band, S-band (TDRSS and Deep Space Network/Ground Network compatible). All communications are based on CCSDS protocols. Like the Terra mission, Aqua provides various means of payload data downlinks, among them Direct Broadcast (DB).
Figure 2: The Aqua spacecraft in launch preparation at VAFB (image credit: NASA)
Launch: The Aqua spacecraft was launched on May 4, 2002 with a Delta-2 7920-10L vehicle from VAFB, CA. Aqua is the second satellite in NASA's series of EOS spacecraft. - Aura, the third of the three large satellites in the EOS series, was launched in July 2004 and is lined up behind Aqua, in the same orbit.
Orbit: Sun-synchronous circular orbit, altitude = 705 km (nominal), inclination = 98.2º, local equator crossing at 13:30 (1:30 PM) on ascending node, period = 98.8 minutes, the repeat cycle is 16 days (233 orbits).
The Aqua spacecraft is part of the "A-train" (Aqua in the lead and Aura at the tail, the nominal separation between Aqua and Aura is about 15 minutes) or "afternoon constellation" (a loose formation flight which started sometime after the Aura launch July 15, 2004). The objective is to coordinate observations and to provide a coincident set of data on aerosol and cloud properties, radiative fluxes and atmospheric state essential for accurate quantification of aerosol and cloud radiative effects.
The PARASOL spacecraft of CNES (launch on Dec. 18, 2004) is part of the A-train as of February 2005. The OCO mission (launch in 2009) will be the newest member of the A-train. Once completed, the A-train will be led by OCO, followed by Aqua, then CloudSat, CALIPSO, PARASOL, and, in the rear, Aura. 4)
Note: The OCO (Orbiting Carbon Observatory) spacecraft experienced a launch failure on Feb. 24, 2009 - hence, it is not part of the A-train.
Figure 3: Illustration of Aqua in the A-train (image credit: NASA)
• August 14, 2018: This series of images shows carbon monoxide (in orange/red) from California's massive wildfires drifting east across the U.S. between July 30 and August 7, 2018. It was produced using data from AIRS (Atmospheric Infrared Sounder) on NASA's Aqua satellite. 5)
Figure 4: AIRS measures concentrations of carbon monoxide that have been lofted high into the atmosphere. These images show the carbon monoxide at a 500 hPa pressure level, or an altitude of ~5,500 m. As the time series progresses, we see that this carbon monoxide is drifting east with one branch moving toward Texas and the other forking to the northeast. The high end of the scale is set to 200 parts per billion by volume (ppbv); however, local values can be significantly higher (image credit: NASA/JPL)
- Carbon monoxide is a pollutant that can persist in the atmosphere for about one month and can be transported large distances. It plays a role in both air pollution and climate change.
- AIRS in conjunction with the AMSU (Advanced Microwave Sounding Unit) senses emitted infrared and microwave radiation from Earth to provide a three-dimensional look at Earth's weather and climate. Working in tandem, the two instruments make simultaneous observations all the way down to Earth's surface, even in the presence of heavy clouds. With more than 2,000 channels sensing different regions of the atmosphere, the system creates a global, three-dimensional map of atmospheric temperature and humidity, cloud amounts and heights, greenhouse gas concentrations, and many other atmospheric phenomena.
• July 31, 2018: The 2018 wildfire season in North America is well under way, with blazes having burned more acres than average through the end of July. Earlier in the summer, satellite images showed smoke and burn scars from fires in western states including California and Colorado. As the calendar turns to August, smoke is now streaming from fires in nearly every western state. 6)
Figure 5: MODIS on NASAS's Aqua and Terra satellites acquired these natural-color images on 28 and 29 July 2018. The animation shows how winds can make smoke plumes vary daily in direction and distance from their source (image credit: NASA Earth Observatory, images by Lauren Dauphin, using MODIS data from LANCE/EOSDIS Rapid Response. Story by Kathryn Hansen)
- A notable amount of the smoke stems from the Carr Fire, which is burning in Shasta County near Redding, California. The fire ignited on July 23 amid warm, dry conditions. By July 30, it had burned 98,724 acres (40,000 hectares) and was just 20 percent contained, according to Cal Fire. News reports noted that shifting, gusty winds and a lack of rain in the forecast could worsen the situation.
- Other states also contributed to the smoke pall over the West. According to the National Interagency Fire Center, 98 large active fires were burning across the United States on July 30, having consumed 1.2 million acres. States with the largest fires counts included Oregon (16), Alaska (15), Arizona (10), Colorado (13), and California (9).
- Most areas of burning land are not directly visible in satellite imagery, obscured from view by smoke and clouds. The Perry Fire in Nevada is an exception; check out these Landsat images to see how the fire advanced over the span of a day.
• July 26, 2018: MODIS on NASA's Aqua satellite captured this natural-color image of ice breaking up on Hudson Bay on 22 July 2018. The image shows a large patch of ice swirling in the southern part of the bay near the Belcher Islands, the curved set of islands in the lower right of the image. 7)
- According to the Canadian Ice Service, ice melt was a few weeks later than normal in northeastern Hudson Bay and along the Labrador Coast, but a few weeks ahead of normal in western and southwestern Hudson Bay. Though the timing of the ice breakup is changing, the bay is usually ice-free by August.
- The rhythms of sea ice play a central role in the lives of the animals of Hudson Bay, particularly polar bears. When the bay is topped with ice, polar bears head out to hunt for seals and other prey. When the ice melts in the summer, the bears swim to shore, where they fast until sea ice returns.
- University of Alberta scientist Andrew Derocher is part of a group that monitors Hudson Bay polar bear populations using information gathered from tagged bears and GPS satellites. In a tweet dated July 20, 2018, he noted that some of the tagged bears were still on the ice floes, while others had made the move to shore.
Figure 6: Sea ice can linger on Hudson Bay into the summer, but it is usually gone by mid-August (image credit: NASA Earth Observatory, image by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response, story by Adam Voiland)
• July 11, 2018: Once a super typhoon, the still powerful Typhoon Maria is expected to make landfall in eastern China on July 11, 2018, with damaging winds and heavy rains. Schools and factories in the city of Fuzhou have been closed; more than 140,000 residents have been evacuated from coastal and low-lying areas; and fishing boats have returned to port in anticipation of the typhoon's arrival. Around 1,500 workers from Fujian Expressway Group are standing by to repair potential damage from the typhoon. 8)
- Maria went through one of the fastest intensifications on record, growing from a tropical storm to a super typhoon in one day. The storm was at its most powerful on July 6 and July 8, when winds exceeded 135 knots (155 miles/250 km per hour). The storm was equivalent to a category 4 hurricane on the Saffir-Simpson scale. The storm has since been downgraded to a typhoon and is expected to weaken some more as it approaches land. Even so, Typhoon Maria is formidable, bringing the potential to damage buildings and knock out power lines.
Figure 7: This image of Typhoon Maria was acquired on July 10, 2018, by the MODIS instrument on NASA's Aqua satellite. The storm already passed by Guam, knocking out power before passing over Japan's southern Ryukyu Islands. The storm was headed for the northern tip of Taiwan and towards the Fujian and Zhejiang provinces of China (image credit: NASA Earth Observatory image by Lauren Dauphin, using MODIS data from LANCE/EOSDIS Rapid Response, story by Kasha Patel)
• May 30, 2018: The Okavango Delta in northern Botswana is one of the world's largest inland deltas. It is known for its annual flooding, which happens between February and May as a wave of water from seasonal rainfall traverses about 20,000 km2 of wetlands. But just as water makes a regular appearance in this part of the Kalahari Desert, so too does fire. 9)
Figure 8: MODIS instruments on NASA's Aqua and Terra satellites acquired this series of images between April 28 and May 23, 2018. The images were composed from a combination of visible and shortwave infrared light (MODIS bands 7-2-1). The burn scar appears dark brown; vegetation is bright green; bare ground is light brown; and water is dark blue (image credit: NASA Earth Observatory, image by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response, story by Kathryn Hansen)
- Notice how water appears to be moving from the areas of permanent swamp and filling the fingers of the so-called seasonal swamp. "The annual flood pulse is reaching the distal fringes of the delta about now," said Michael Murray-Hudson, a wetlands ecologist at the University of Botswana's Okavango Research Institute. At the same time, a slow-moving fire front (bright orange) is advancing toward the southeast, leaving a dark brown burn scar in its wake.
- Also notice how the path of the fire appears to follow the path of the floodplain. Channels inundated with floodwater can generate a huge amount of vegetation that is prone to burning. But there is a sweet spot: researchers have shown that floodplains inundated with water on an intermediate basis—about every other year—have the highest potential to burn.
- While the floodwaters help to generate the fuel needed for burning, the fires ultimately have a human origin. "Almost all of the fires are anthropogenic," Murray-Hudson said. "People set them when they can, for example, when the landscape will carry a fire. It's a pretty normal phenomenon, although the extent and frequency might be increasing as the human ecological footprint in the delta grows."
- Previous research suggests that fires can affect the ecosystem by changing the quality of floodplain water and by removing aquatic shelter for young, vulnerable fish. But the authors of that paper point out: "The amount of seasonal flooding has a larger ecosystem impact than fires and is the primary factor in the wetland's productivity."
• April 26, 2018: On some hazy days, particularly in winter, China's skies are blanketed by white and gray clouds of air pollutants. New research shows that such smog not only dims the daylight and makes the air hard to breathe, but it reduces the amount of sunlight reaching China's solar panels. 10)
- In the new study, researchers at Princeton University examined how solar power resources in China are affected by atmospheric aerosols — small liquid and solid particles that can scatter sunlight back into space or increase cloud formation. The researchers used surface irradiance data from NASA's CERES (Clouds and the Earth's Radiant Energy System) on Aqua and a computer model that calculates the impact of aerosols and clouds on surface radiation by examining the amount of solar energy falling on Earth's surface.
- The visualization at the top of the page shows the average effect of aerosols on the amount of radiation reaching the land surface of China between 2003 and 2014. Northwestern and eastern China, the nation's most polluted regions, experienced the biggest dips. The researchers found that in the most polluted areas, available solar energy decreased as much as 35 percent, or 1.5 kWh/m2/day. That is enough energy to power a vacuum cleaner for one hour, wash twelve pounds of laundry, or run a laptop for five to 10 hours.
- The results surprised the team. "When I asked around before conducting this study, people did not think aerosols would be a big deal in reducing solar energy potential," said Xiaoyuan (Charles) Li, the lead author of the paper and who recently graduated from Princeton with a PhD in Environmental Engineering. "There are a lot of cloudy days in China, and clouds are considered to be the major factor in reducing surface solar radiation."
Figure 9: Study of the reduction in photovoltaic generation in China due to aerosols as observed by CERES on NASA's Aqua satellite in the period 2003-2014 (image credit: NASA Earth Observatory image by Joshua Stevens, using data from Li, Xiaoyuan, et al. (2017)
Figure 10: Reduction in photovoltaic capacity factor due to Aerosols and Clouds by Grid (image credit: NASA Earth Observatory image by Joshua Stevens, using data from Li, Xiaoyuan, et al. (2017)
- But the study showed that wintertime aerosols had nearly the same sunlight-blocking effect as clouds in northern China, as shown in the graphs above. Li noted that aerosols are more prevalent in China in the winter because coal is often burned for heat. In Beijing, the mountainous terrain also traps air masses, making it harder to blow aerosols away from the surface.
Figure 11: This natural-color image above shows thick haze over eastern China on January 25, 2017, as observed by the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite. Milky, gray smog blankets many of the valleys and lowlands. Atmospheric gases and pollutants are trapped near the surface in basins and valleys (image credit: NASA image by Jeff Schmaltz, LANCE/EOSDIS Rapid Response, story by Kasha Patel)
- "As China's current efforts in fighting air pollution continue the benefit is not only for human health, but could also improve the efficiency of solar panels," said Li. By addressing its air pollution problem, China could improve its chances to meet its goal of producing 10 percent of the nation's electricity through solar energy by 2030.
• April 22, 2018: If you were standing outside in the Mid-Atlantic region on April 17, 2018, and looked up in the afternoon, you may have noticed long, linear rows of clouds overhead. The clouds looked pretty remarkable from above as well. 11)
Figure 12: MODIS on NASA's Aqua satellite captured this image of the wave clouds. Below the clouds, signs of spring washed through the region, with forests in the Piedmont of North Carolina and Virginia showing widespread greening even as the cooler mountain areas remained brown. In the large image, the abundance of farms in the coastal plain gives that region a yellower color (image credit: NASA Earth Observatory, image by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response, story by Adam Voiland)
- "Holy gravity waves" was how meteorologist Dakota Smith put it, when he tweeted an animation of satellite imagery that showed the wave clouds rippling through the atmosphere. (Gravity wave is a term used to describe waves generated in a fluid medium where the force of gravity or buoyancy tries to restore equilibrium.)
- Wave clouds form when air flows over a raised landform. In this case, the northwesterly winds of the jet stream passed over the Appalachians and made gravity waves on the lee (east) side of the mountains. When the air hit the edge of the mountains and began to pass over, it began to oscillate—much like the suspension of a car bounces after it goes over a speed bump.
- There is a particular height in the atmosphere at which the air is saturated and clouds form—the lifting condensation level. Wave clouds form when the crests of the waves rise above that level, even as the troughs of the wave remain below it. The horizontal spacing of the waves offers a clue about the speed of the winds passing over the mountains. Higher wind speeds yield wave clouds with more space between each row.
- "You need relatively strong winds to generate the gravity waves," said Grant Gilmore, a meteorologist with WTSP, a television station in St. Petersburg, Florida. "The jet stream—even a jet streak—was almost directly over where these gravity waves formed on the 17th."
• April 2, 2018: In the Gulf of Aden, the largest phytoplankton blooms tend to show up in mid-summer near the coast of Yemen and in mid-autumn near the coast of Somalia. But blooms can happen in other seasons as well, including winter. 12)
- A winter phytoplankton bloom is visible in this image of Figure 13, composed from data acquired on February 12, 2018, by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite. A series of processing steps were applied to the data to highlight color differences and to bring out the bloom's subtle features. The image shows phytoplankton swirling in this Gulf on the western end of the Arabian Sea.
- Without a water sample and analysis, it is impossible to know for sure what type of phytoplankton composed this bloom. "NASA hopes to, some day, be able to better identify different types of phytoplankton from orbit through hyperspectral instruments designed specifically for ocean-color remote sensing," said Norman Kuring, an ocean scientist at NASA's Goddard Space Flight Center. "The Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission, currently in development, is such an endeavor."
Figure 13: MODIS image of a winter phytoplankton bloom, acquired on 12 Feb. 2018 in the Gulf of Aden (image credit: NASA Earth Observatory, Gene C. Feldman)
- On the same day that the satellite image was acquired, researchers working from a ship in a northern part of the Arabian Sea identified a bloom of Noctiluca scintillans stretching from the coast of Oman to India. Joaquim Goes, a biological oceanographer at Lamont Doherty Earth Observatory, provided the photograph below. It shows the N. scintillans bloom on February 12, 2018, as seen offshore from Muscat, Oman.
- The field work was part of the Decision and Information System for the Coastal waters of Oman (DISCO), a collaborative project supported by NASA Applied Sciences, and in partnership with Sultan Qaboos University and with Oman's Ministry of Agriculture and Fisheries Wealth. The project aims to develop models that can be used to forecast harmful algal blooms.
- Understanding how blooms vary in composition, size, location, and timing is important for knowing how their presence or absence affects marine ecosystems and fisheries. Phytoplankton can be an important source of food for marine mammals, shellfish, and fish. N. scintillans, however, has been shown to be harmful to fish and marine invertebrates. And some blooms can be so thick that they clog desalination plants in the Arabian Sea.
Figure 14: On the same day that the satellite image was acquired, researchers working from a ship in a northern part of the Arabian Sea identified a bloom of Noctiluca scintillans stretching from the coast of Oman to India (image credit: NASA's Ocean Biology Processing Group, image by Joaquim Goes, story by Kathryn Hansen)
• March 30, 2018: Sea ice in the Arctic Ocean grows each year throughout the fall and winter and reaches its maximum extent sometime between February and April. This year, sea ice peaked on March 17, 2018, at 14.48 million km2, making it the second-lowest maximum on record. There was still enough ice, however, to cool the air and help produce cloud streets—long, parallel bands of cumulus clouds that commonly form this time of year when cold air blows over warmer water. 13)
- On March 15, 2018, two days before sea ice reached its maximum extent, the MODIS instrument on NASA's Aqua satellite acquired this image of cloud streets over the Barents Sea (Figure 15). According to the NSIDC (National Snow & Ice Data Center) in Boulder, CO, this region had a late spurt of sea ice growth. When this image was acquired, cool air was blowing southward across the sea ice and over the comparatively warmer open water off of northern Europe.
- Ultimately, cloud streets are the visible result of nature trying to balance differences in energy. Columns of heated air called thermals rise through the atmosphere, moving heat away from the sea surface. The air masses rise until they hit a warmer air layer (temperature inversion). This layer acts like a lid, causing the rising thermals to roll over and loop back on themselves forming parallel cylinders of rotating air. On the upper side of these cylinders (rising air), clouds form. Along the downward side (descending air), skies are clear.
- Notice, too, the variation in sea ice across the Barents and Kara seas. In contrast to the Barents, ice in the Kara Sea (east of the Novaya Zemlya archipelago) is still solid. The image of Figure 16 shows a detailed view of sea ice near Russia. Light gray areas that resemble shadows north of Kolguyev Island are more likely due to sea ice that has been thinned by offshore winds.
Figure 15: The MODIS instrument acquired this image of cloud streets over the Barents Sea on 15 March 2018 (image credit: NASA Earth Observatory, images by Jeff Schmaltz, using MODIS data from LANCE/EOSDIS Rapid Response, caption by Kathryn Hansen)
Figure 16: Detail image of sea ice near Russia (image credit: NASA Earth Observatory)
• In late March 2018, the people of Eastern Europe and Russia found their snow cover had a distinctly orange tint. The color came from vast quantities of Saharan dust that were picked up by strong winds, lofted over the Mediterranean Sea, and deposited on Bulgaria, Romania, Moldova, Ukraine, and Russia. Skiers in the Caucasus Mountains snapped photos that looked like they could have come from the Red Planet. 14)
- The MODIS instrument on NASA's Aqua satellite acquired a natural-color image of the dusty snow in Eastern Europe on March 24, 2018 (Figure 17). The MODIS instrument on the Terra satellite acquired the image of Figure 18, a natural-color view of dust from North Africa blowing across the Mediterranean Sea on March 26, 2018. Dust storms were still raging on March 27, as shown by another Terra image of the Black Sea region.
- In Greece, Crete, and Cyprus, the airborne particles significantly reduced visibility for days, and people described tasting dust as they walked outside, news media reported. Authorities cautioned children, the elderly, and people with respiratory diseases to stay indoors as much as possible. According to several news accounts, the Athens Observatory called this event one of the largest dust deposits on record in Greece.
- South and southwest winds associated with a low-pressure weather system appeared to fuel the flow of dust into Europe. Those dust plumes were visibly mingled with cloud cover over the Black Sea in a March 23 image from the Suomi NPP satellite. Some of the airborne dust mixed into the snow and rain that fell on the region on March 23–24. The Ozone Mapping & Profiler Suite (OMPS) on Suomi NPP detected high levels of airborne aerosols over the region from March 20–25.
- Dust storms are common in the Sahara in the springtime, as the weather changes with the seasons. Large dust events tend to occur about every five years, though multiple observers described this one as particularly intense.
Figure 17: MODIS image on Aqua, acquired on 24 March 2018 showing the dusty snow over Eastern Europe (image credit: NASA Earth Observatory, images by Jeff Schmaltz, LANCE/EOSDIS Rapid Response. Story by Mike Carlowicz)
Figure 18: The MODIS instrument on NASA's Terra satellite acquired this image, a natural-color view of dust from North Africa blowing across the Mediterranean Sea on March 26, 2018 (image credit: NASA Earth Observatory, images by Jeff Schmaltz, LANCE/EOSDIS Rapid Response. Story by Mike Carlowicz)
• March 20, 2018: In a reversal from abundant snow conditions in February 2017, the snowpack in Afghanistan in February 2018 was the lowest detected for the month since 2001. That is a concern heading into spring and summer, as snowmelt is an important source of water for crops and irrigation. 15)
- The drought is apparent in these maps of "snow water equivalent"—the depth of water that would result if the snow were to completely melt. The top-right map shows conditions on February 21, 2018, amid a low snowpack; the top-left map shows conditions on February 21, 2017. The darkest blue areas indicate where the snow contained the most water. Turn on the image comparison tool to see the difference.
- Scientists cannot make direct, physical measurements of snowpack everywhere on the planet. That is where models can help. By combining remotely sensed observations of precipitation, temperature, solar radiation, and wind with information about elevation and topography, a model can estimate how much snow is present. From this, scientists calculate theSWE (Snow Water Equivalent). These estimates can help experts infer where there might be flooding when the snow melts. Conversely, they can help them anticipate and plan for drought if SWE levels are low.
Figure 19: The Aqua satellite image on the right shows conditions on February 21, 2018, amid a low snowpack; the left map shows conditions on February 21, 2017 (image credit: NASA Earth Observatory, images by Joshua Stevens, using LSM (Land-Surface Model) data courtesy of Amy McNally, Jossy Jacob, and the NASA Land Information System, and temperature anomalies from the Early Warning and Environmental Monitoring (EWEM) program at the USGS, story by Kathryn Hansen)
- The low snowpack this year is not entirely a surprise; low snowpack often coincides with periods of La Niña. The chart of Figure 20 shows the progression of snow water equivalent in water year 2018 (red line) and water year 2017 (orange line). (A water year begins on October 1 to align with hydrologic seasons.) The blue dashes indicate the average snow water equivalent between 2001-2017.
- Notice how snow levels started off slow in early 2018 and 2017 (also amid La Niña conditions). The difference was that in early February 2017, a huge amount of snow fell on Afghanistan. The storm was so extreme that it spurred avalanches that buried villages. That one event was enough to bring snow levels back up to average. In comparison, snowfall in February 2018 increased somewhat but accumulations were still at a record low.
- NASA data also show that temperatures this winter have been hotter than usual in the region. The temperature anomaly maps of Figure 21 are based on data from the MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Aqua satellite. It shows LSTs (Land Surface Temperatures) for February 2018 (right) and February 2017 (left), compared to the average since 2002 for the same month. Red colors depict areas that were hotter than average; blues were colder; white pixels were normal. USAID's FEWSNET (Famine Early Warnings Systems Network) reported that the high temperatures are expected to deplete the snowpack "sooner than normal, resulting in possible irrigation water shortages in April and May."
- "While a big snow event is still possible this year, we're now midway into March and temperatures are rising, so it is unlikely," said Amy McNally, a researcher who produces the snow estimates for the Land Information System at NASA/GSFC (Goddard Space Flight Center). "At this point, rain may provide some water for the early part of the growing season, but we'd still be concerned about later in the season, given that we don't have the water stored in the snow pack."
- Various groups are keeping an eye on the situation as the country enters the latter part of the wet season (October to May). A March hazard outlook from the NOAA Climate Prediction Center states: "A drought hazard is posted over much of Afghanistan and portions of adjacent countries as the ongoing, large moisture deficits are likely to negatively impact crops over the coming months."
Figure 21: Aqua MODIS LSTs (Land Surface Temperatures) for February 2018 (right) and February 2017 (left), compared to the average since 2002 for the same month. Red colors depict areas that were hotter than average; blues were colder; white pixels were normal (image credit: NASA Earth Observatory, Ref. 15)
• February 16, 2018: Media reports have described the many ways that cold temperatures have affected the 2018 Olympic Winter Games in Pyeongchang, South Korea. Razor-sharp, icy snow crystals have damaged skis, and some concert goers suffered from hypothermia prior to the opening ceremony. The region is known to be cold and dry; temperatures in February in Pyeongchang average -5.5 degrees Celsius . But NASA data show that the temperatures in the first days of the winter games have been colder than usual. 16)
- The temperature anomaly map of Figure 23 is based on data from the MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite. It shows land surface temperatures (LSTs) from January 29 to February 5, 2018, compared to the 2010–2018 average for the same eight-day period. Red colors depict areas that were hotter than average; blues were colder than average; and white pixels were normal.
Figure 22: MODIS image of Korea on Terra, acquired on 5 Feb. 2018 (image credit: NASA Earth Observatory, image by Joshua Stevens, using data from the Level 1 and Atmospheres Active Distribution System (LAADS) and LANCE/EOSDIS Rapid Response. Story by Kathryn Hansen)
- The map shows that colder-than-average temperatures prevailed across most of the Korean Peninsula. The line chart shows how land surface temperatures in the city changed over the course of a year. Early February 2018 is clearly colder than the same time in 2017.
Figure 23: Temperature anomaly map based on MODIS data showing the LST from January 29 to February 5, 2018, compared to the 2010–2018 average for the same eight-day period (Image credit: NASA Earth Observatory)
- Cold is not the only factor affecting the games. Wind gusts up to 80 km/hour have ripped through the region and caused some of the skiing events to be delayed or postponed. The natural-color image of Figure 24 was acquired on February 13, 2017, by MODIS on the Aqua satellite. Clouds over land appear to moving in the same direction as the winds, which frequently blow from Siberia toward the southeast.
- Snow is also visible in Pyeongchang, located amid the Taebaek Mountains, the site of the skiing and snowboarding events, as well as the opening ceremonies. There is visibly less snow on the coastal plain near Gangneung, the site of Olympic ice events. See a detailed view of these two regions here.
- Scientists in NASA's Short-term Prediction Research and Transition Center (SPoRT) have been tracking temperature, winds, and snowfall in Pyeongchang. Their aim is to use observations and models to improve short-term, regional forecasts. You can read more about their work as it pertains to Pyeongchang on their blog and browse the output of their real-time weather model.
- The modeling research is part of a larger effort by Earth science researchers who are conducting experiments and making observations during the games. The International Collaborative Experiments for Pyeongchang 2018 Olympic and Paralympic Winter Games (ICE-POP 2018) is a scientific field campaign taking place in Korea in February and March to study mountain-induced snowfall and other weather phenomena in the region. Read about their efforts on Earth Observatory's ICE-POP blog, written by the scientists currently in the field.
Figure 24: MODIS image on the Aqua satellite acquired on 13 Feb. 2018 (image credit: NASA Earth Observatory image by Joshua Stevens, using data from the Level 1 and Atmospheres Active Distribution System (LAADS) and LANCE/EOSDIS Rapid Response. Story by Kathryn Hansen)
• January 21, 2018: Ships churning through the Atlantic Ocean produced this patchwork of bright, crisscrossing cloud trails off the coast of Portugal and Spain. The narrow clouds, known as ship tracks, form when water vapor condenses around tiny particles of pollution that ships emit as exhaust or that form from gases in the exhaust. Ship tracks typically form in areas where low-lying stratus and cumulus clouds are present. 17)
- Some of the pollution particles generated by ships (especially sulfates) are soluble in water and serve as the seeds around which cloud droplets form. Clouds infused with ship exhaust have more and smaller droplets than unpolluted clouds. As a result, the light hitting the polluted clouds scatters in many directions, making them appear brighter and thicker than unpolluted marine clouds, which are typically seeded by larger, naturally occurring particles such as sea salt.
- Several shipping lanes intersect in the waters off the coast of Portugal. Visualizations of ship traffic show large numbers of ships entering and exiting the Mediterranean Sea in this region. Many of them hug the coast of the Iberian Peninsula as they travel toward ports in northern Europe. In this case, the large volume of ships along the coast appear to have brightened the clouds so much that it is difficult to distinguish individual ship tracks. The more visible tracks are several hundred kilometers offshore, and many of these appear to be created by ships heading out of the Mediterranean Sea toward North America. Others are probably the result of ships from South America and Africa charting courses toward northern Europe.
- The MODIS instrument aboard the Aqua satellite captured this natural-color image on January 16, 2018 (Figure 25). Some of the crisscrossing clouds stretch hundreds of kilometers from end to end. The narrow ends of the clouds are youngest, while the broader, wavier ends are older.
- Age is not the only factor that affects the appearance of ship tracks. NASA scientists have identified specific atmospheric conditions that affect their brightness, or albedo. One key factor is the structure of clouds already in the area. Ship tracks clouds that form near open-cell clouds—many of which are present in this image—tend to be brighter than those that form near close-celled clouds. (Open-cell clouds look like empty compartments, whereas closed-cell clouds look like compartments stuffed with clouds.)
- The high reflectivity of ship track clouds means they shade Earth's surface from incoming sunlight, which produces a local cooling effect. However, determining whether ship tracks have a global cooling effect is challenging because the way particles affect clouds remains one of the least understood and most uncertain aspects of climate science.
Figure 25: The MODIS instrument aboard the Aqua satellite captured this natural-color image on 16 January 2018, crisscrossing cloud trails off the coast of Portugal and Spain (image credit: NASA Earth Observatory, image by Jeff Schmaltz, LANCE/EOSDIS Rapid Response. Story by Adam Voiland)
• December 13, 2017: After more than a week of burning, the wildfires in Southern California continue to loft a nasty mixture of aerosols and gases into the atmosphere. 18)
- On December 11, 2017, MODIS on NASA's Aqua satellite acquired a natural color image (left) of smoke billowing from the Thomas Fire in Ventura County, California. By that day, the fire had already burned 230,500 acres (93,000 hectares = 930 km2 or 360 square miles).
- The corresponding map of Figure 26 (right) shows the concentration of carbon monoxide in the area, based on data collected by the AIRS (Atmospheric Infrared Sounder) on Aqua. The concentrations reflect total "column" amounts of the gas, measured vertically through the atmosphere by AIRS. Orange areas indicate the highest concentrations of carbon monoxide.
- When fires burn through a fuel source — such as vegetation, gasoline, or coal — emissions can include everything from hydrocarbons, nitrogen oxides, and carbon monoxide. Close to the source of the fire, the air quality on that day was rated unhealthy. As the image pair shows, smoke and carbon monoxide appear offshore as well.
- Dejian Fu, an atmospheric scientist at NASA/JPL (Jet Propulsion Laboratory), thinks that the carbon monoxide plume likely stemmed from the burning onshore and then blew out over the Pacific Ocean. This map shows the gas concentration up to an altitude of about 5 km above the surface.
- Carbon monoxide contributes to reactions that produce ground-level ozone, a harmful pollutant. It can also make breathing difficult to dangerous when trapped near the ground.
Figure 26: The left map is a MODIS natural color image of the Ventura fire, the corresponding right map shows the concentration of carbon monoxide in the area acquired with AIRS. Aqua acquired these data on 11 Dec. 2017 (image credit: NASA Earth Observatory, images by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response and AIRS data from the Goddard Earth Sciences Data and Information Services Center (GES DISC), story by Kathryn Hansen)
• December 8, 2017: About 250 km from the Antarctic mainland, the ice-capped tops of the Balleny Islands protrude from the Southern Ocean. Located near the intersection of opposing wind and current systems, the archipelago's three main islands can be battered by weather from all sides. 19)
- But when satellites acquired these images on November 26, 2017, the winds were probably not that turbulent, allowing the formation of organized wave patterns in the clouds and at the ocean's surface. Jan Lieser, a marine glaciologist from Australia's Antarctic Climate and Ecosystems Cooperative Research Center, noticed the curious patterns while browsing satellite images.
Figure 27: This image shows a wave pattern in the clouds, as observed by MODIS on NASA's Aqua satellite. The image, acquired on 26 Nov. 2017, is false-color, using MODIS bands 7-2-1 to help distinguish clouds (white) from sea ice (blue), image credit: NASA Earth Observatory, image by Joshua Stevens, using MODIS data from LANCE/EOS DIS Rapid Response, story by Kathryn Hansen
- Jan Lieser thinks that a laminar, eastward flow of air hit a speed-bump—Sturge Island—which triggered a low frequency wave pattern to form on the island's lee side. The flow's upper layers reached high enough for water vapor to condense and form clouds. The wave ridges are spaced about 15 km apart and persist for about 200 km east of the island.
- "The cloud pattern can be compared to a lonesome ship sailing on an otherwise smooth lake or ocean and creating these well-known wave traces behind it," Lieser said. "Except here it's the medium (air) that is flowing around the obstacle (island) and not the disturbance (ship) travelling though the medium (water surface)."
- The phenomenon is not entirely unusual. Perhaps more notable is that the pattern also shows up on the ocean surface. Sea surface waves are visible in the image of Figure 28, acquired on the same day by the SAR (Synthetic Aperture Radar) on the European Space Agency's Sentinel-1B satellite. SAR can penetrate clouds to map surfaces below.
- The grayscale image represents differences in surface roughness. The roughest surfaces, particularly Sturge Island, appear brightest. Smoother surfaces—such as sea ice and parts of the open water—appear dark. Roughness also shows up in a wave-pattern across areas of open water, and in the cracks and openings between the sea ice floes.
- Jan Lieser thinks that the same wind that rippled in the sky to form clouds behind the island also came down and roughened the water surface. "If there was a dinghy on the open water east of Sturge Island at the time," he said, "I suspect the sailor would have experienced long-period trains or rippled water passing by and interchanging with smooth periods on an otherwise calm and pleasant day."
Figure 28: Sentinel-1B SAR image of the Sturge Island region, acquired on 26 Nov. 2017, showing the sea surface waves corresponding to the cloud patterns of Figure 27 (image credit: NASA Earth Observatory, image by Joshua Stevens, using modified Copernicus Sentinel data (2017) processed by the European Space Agency)
• November 16, 2017: Though much of eastern North America just endured a wintry cold snap, it was not that long ago that the weather felt summery. In fact, it was just two weeks ago—well into autumn. 20)
- Weather records fell across the northeastern United States and Canada's Quebec and Maritime provinces in October 2017. According to the U.S. NCEI (National Centers for Environmental Information), the month was the warmest on record (since 1895) for all six New England states. Maine, New Hampshire, Massachusetts, Vermont, Rhode Island, and Connecticut all witnessed monthly average temperatures that were 4.2-4.4ºC above the 20th century average.
- Temperatures also were much warmer than average in the Mid-Atlantic and Great Lakes regions, as well as the far Southwest. At least 20 cities—including Burlington, Albany, Portland, and New York City—set new October records. In contrast, six cities in the Rocky Mountains reported October temperatures that were among their top-10 coldest.
- Environment Canada reported that dozens of cities across eastern Canada had their warmest September and October on record, including Ottawa, Montreal, Quebec, Fredericton, and Halifax. The long-term average temperature in Montreal across both months is typically 12.0°C, but this year the city saw a record-breaking average of 15.9°C. Similarly, Ottawa measured a two-month average of 14.5°C, compared to the long-term average of 11.5°C. Toronto fell just short of its warmest September and October on record.
- The nationally averaged U.S. temperature for October 2017 was 13.2°C, which is 0.9°C above the 20th century average. The warm October temperatures in Canada and the U.S. Northeast were attributed to a strong ridge of high pressure that caused a large northward bulge in the jet stream.
- According to NCEI, the span of January through October has been the third warmest and second wettest on record for the lower 48 United States.
- The map of Figure 29 shows land surface temperature anomalies for October 2017 compared to the average conditions for all Octobers between 2002-2016. The measurements represent the temperature of the top 1 millimeter of the land surface during the daytime. LSTs (Land Surface Temperatures) should not be confused with air temperatures; LSTs reflect the heating of forests, grasslands, cities, and bare ground by sunlight, and they can sometimes differ significantly from air temperatures.
Figure 29: The data come from AIRS (Atmospheric Infrared Sounder) on NASA's Aqua satellite. AIRS is a hyperspectral infrared sensor that observes atmospheric and surface conditions at 2,378 separate wavelengths. This makes it possible for scientists to create three-dimensional temperature profiles that go from the surface to 40 km in altitude (image credit: NASA Earth Observatory, image by Joshua Stevens, using AIRS data from the Goddard Earth Sciences Data and Information Services Center (GES DISC). Story by Mike Carlowicz. Special thanks to climatologist David Phillips of Environment Canada)
• November 15, 2017: Scientists first reported major dust storms in southern Alaska in 1911, but only during the past decade have they begun to find that high-latitude dust storms play a role in fueling phytoplankton blooms. In 2011, Santiago Gassó of NASA's Goddard Space Flight Center, John Crusius of the U.S. Geological Survey, and other scientists published the first study to describe how dust storms play a role in supplying nutrients, particularly iron, to the Gulf of Alaska. Since then, each successive dust storm has offered these scientists new opportunities to tease out details of the complicated relationship between dust and Gulf of Alaska phytoplankton. 21)
- On November 11, 2017, MODIS (Moderate Resolution Imaging Spectroradiometer ) on NASA's Aqua satellite captured this image of the coast along the Gulf of Alaska (Figure 30). Thick plumes of dust—mainly fine-grained loess formed when glacial ice pulverizes rock—blew south from river valleys. Dust storms in southern Alaska generally occur in late fall, when river levels are relatively low, snow has not yet fallen, and layers of loess-rich mud are exposed to the wind.
- Since light is also crucial to phytoplankton growth, Gassó and his colleagues propose that the influence of dust falling in the ocean may be delayed until the following spring. To get a better understanding of the relationship, the scientists are trying to determine how much iron is supplied by dust storms, as compared to the upwelling of nutrient-rich water from the depths or the mixing of iron-rich sediments (runoff from rivers) by surface eddies and gyres. However, the latter phenomena tend to be coastal, whereas wind-blown dust can cross hundreds of miles of open ocean to areas where iron is normally depleted.
- "It is convenient that we have a phenomenon happening right in our backyard that lends itself to studying the factors that controls marine phytoplankton growth," said Gassó, noting that much of the research on this topic has been done in the Southern Ocean around Antarctica.
- Studying modern dust storms can also make scientists better at interpreting ice cores, which record past environmental conditions and changes in climate. Many ice samples show evidence of both increased dust deposition and decreased concentrations of carbon dioxide in the air during glacial periods (ice ages). It is not yet clear why increased dust and low levels of atmospheric carbon dioxide would go hand-in-hand, but some scientists think that dust-triggered phytoplankton blooms, which can absorb large amounts of carbon dioxide, may have played a key role.
Figure 30: The MODIS instrument on the Aqua satellite captured the dust storm in the Gulf of Alaska on 11 Nov. 2017 (image credit: NASA Earth Observatory, image by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response. Story by Adam Voiland)
• November 1, 2017: The waters off of southwestern Africa are some of the most biologically productive and chemically interesting in the world. They also provide a compelling backdrop for exploring how satellite sensors and creative data processing can reveal important details of the ocean. 22)
- Flowing up the coast of South Africa, Namibia, and Angola, the Benguela Current is the eastern boundary of a large gyre in the South Atlantic Ocean. The current mixes water from the Atlantic and Indian Oceans as they meet off the capes of South Africa. Thanks to this current and to prevailing winds out of the southeast, this portion of the Atlantic is an area of ocean upwelling.
- Warm surface waters are driven away from the coast, allowing cooler, nutrient-rich waters to rise up from the seafloor. Plumes of hydrogen sulfide sporadically burst from the oxygen-starved depths, a result of bacteria consuming organic material near the bottom and the natural pumping action of upwelling. Air temperatures along the desert coast of southwest Africa are also moderated by the cooler water.
- This dynamic wind and water action causes the ocean to teem with life, from plankton to fish to whales. It all starts with phytoplankton, floating plant-like microorganisms that provide the core source of food for marine ecosystems. The phytoplankton find a near-perfect blend of nutrients, water temperatures, and sunlight to fuel massive blooms. They often show themselves to satellites as an abundance of chlorophyll, the green pigment that helps plants convert sunlight to energy.
- The data for all of the images on this page were acquired by the MODIS instruments on NASA's Aqua satellite on September 2, 2017. The sensor observes Earth in 36 different spectral bands; photo-like imagery is most often built from data in the first seven bands.
- The image of Figure 31 shows the Benguela Current region in natural-color, combining red, green, and blue light (MODIS bands 1-4-3) much as you might see with the human eye. Near the coast, you can see a dark shade of green indicating chlorophyll-rich water. Farther from the coast, the patches of green are harder to detect due to thin clouds and sunglint—the reflection of sunlight back at the MODIS imager (radiometer).
Figure 31: MODIS image of the south-west coast of Africa and the South Atlantic Ocean acquired on 2 September 2017 (image credit: NASA Earth Observatory, images by Jesse Allen, using data from the Level 1 and LAADS (Atmospheres Active Distribution System), and ocean imagery by Norman Kuring, NASA's Ocean Color web, story by Mike Carlowicz)
- Figure 32 shows concentrations of chlorophyll in the ocean. MODIS instruments have been flying in space since 1999, and other ocean-color detecting instruments have been flying for more than three decades. Over those years, scientists have refined data processing and computer algorithms to better distinguish the light reflected and emitted by chlorophyll from other colors of light detected in the ocean. The result is that it is easier to see the details and hidden abundances of chlorophyll (and therefore, phytoplankton) in the water.
Figure 32: MODIS image of the south-west coast of Africa and the South Atlantic Ocean acquired on 2 September 2017 (image credit: NASA Earth Observatory, images by Jesse Allen, using data from the Level 1 and LAADS (Atmospheres Active Distribution System), and ocean imagery by Norman Kuring, NASA's Ocean Color web, story by Mike Carlowicz)
- The image of Figure 33 is a blend of art and science. Like a photographer adjusting lighting and using filters, Norman Kuring of NASA's Ocean Biology group works with various software programs and color-filtering techniques to draw out the fine details in the water. The detailed swirls in the chlorophyll-rich water are all quite real; Kuring simply separates and enhances certain shades and tones in the radiometer data to make the biomass more visible.
- "There is some scientific value in this sort of processing in the qualitative sense," Kuring notes. "For example, I have sent these qualitative, feature-rich images to scientists on research cruises to help them plan their cruise tracks. When sampling the open ocean, researchers often want to drop their instruments into frontal regions where the most interesting phenomena occur. Images like these make such regions more apparent by enhancing gradients."
- "But my main goal in making images like these is to pique the viewer's interest and, hopefully, make them more curious about the ocean," Kuring added. "Even folks who have spent their whole lives studying the ocean only know a tiny bit about it. So the more minds that think ‘I wonder why?' the better."
Figure 33: MODIS image of the south-west coast of Africa and the South Atlantic Ocean acquired on 2 September 2017 (image credit: NASA Earth Observatory, images by Jesse Allen, using data from the Level 1 and LAADS (Atmospheres Active Distribution System), and ocean imagery by Norman Kuring, NASA's Ocean Color web, story by Mike Carlowicz)
• August 30, 2017: Infrared data provides temperature information and the highest, coldest cloud tops in tropical cyclones indicate where the strongest storms are located. NASA's AIRS instrument provides that critical temperature information and captured an image of Harvey within the hour of its landfall in southwestern Louisiana. Harvey made landfall just west of Cameron, Louisiana at 4 a.m. CDT, Aug. 30. 23) 24)
- AIRS found cloud top temperatures as cold as minus 53º Celsius. Storms with cloud top temperatures that cold have the capability to produce heavy rainfall. The strongest storms were around Harvey's center of circulation and in a band of thunderstorms east of the center over southern Mississippi, Alabama and the western-most part of the Florida Panhandle.
Figure 34: This infrared image of Tropical Storm Harvey occurred at the same hour of landfall in southwestern Louisiana. The AIRS instrument aboard NASA's Aqua satellite captured this image on Aug. 30 at 4:17 a.m. EDT (08:17 UTC), and purple indicates the strongest storms (image credit: NASA/JPL, Ed Olsen)
- DLR (German Aerospace Center) is assisting the USGS (U.S. Geological Survey) with before and after flood data from the German radar satellite TerraSAR-X. DLR is supporting hurricane disaster management in Texas. The image was color-coded to show the flooded areas and the waterways.
Figure 35: DLR provided before and after satellite data for Hurricane Harvey (image credit: DLR)
Legend to Figure 35: In anticipation of the catastrophic Hurricane Harvey, the International Charter 'Space and Major Disasters' was activated early on the evening of 24 August 2017. This was initiated by the Charter member United States Geological Survey (USGS) on behalf of the Texas Emergency Management Council. DLR provided real-time recordings and archive data from the German radar satellite TerraSAR-X, which enabled a detailed analysis and an overview of the flood situation. Using these and other satellite data provided by 16 Charter members, the Center for Space Research at the University of Texas is currently working on providing assistance and information to disaster relief personnel on the ground.
"The various recording modes of the German radar satellite TerraSAR-X make it possible to react very flexibly to individual crisis situations," explains André Twele, who, as an ECO (Emergency On-Call Officer) of the Charter at DLR, was tasked with preparing an acquisition plan using available satellite resources in the first hours of activation. "The challenge herein lies in determining possible disaster areas as early as possible from the initially still rough forecast of the hurricane's path to be able to plan the satellite recordings effectively." 25)
• August 25, 2017: Hurricane Harvey continues to churn toward the Texas coast, and is expected to make landfall as a major hurricane sometime late Aug. 25 or early Aug. 26, according to the National Hurricane Center. It would be the first major hurricane to make landfall in the United States since 2005. 26)
- The rapid intensification of Harvey is depicted in this set of false-color images from NASA's AIRS (Atmospheric Infrared Sounder) and AMSU (Advanced Microwave Sounding Unit) instruments on NASA's Aqua satellite. The earlier images were acquired at 3:05 p.m. CDT [(Central Daylight Time), 19:05 UTC] on, Aug. 23, when Harvey became a tropical storm soon after crossing from the Yucatan Peninsula over warm waters in the Gulf of Mexico. The later images were acquired at 2:59 a.m. CDT (7:59 UTC) on Friday, Aug. 25, when Harvey was a Category 2 hurricane.
Figure 36: Hurricane Harvey as seen by the AIRS infrared instrument on NASA's Aqua satellite at 3 p.m. CDT on Wednesday, Aug. 23 (left) and at 3 a.m. CDT on Friday, Aug. 25 (right). The darker the color, the colder and higher the clouds and the stronger the thunderstorms (image credit: NASA/JPL-Caltech)
Figure 37: Hurricane Harvey as seen by the AMSU microwave instrument on NASA's Aqua satellite at 3 p.m. CDT on Wednesday, Aug. 23 (left) and at 3 a.m. CDT on Friday, Aug. 25 (right). Blue indicates areas of heavy rainfall beneath the coldest clouds (image credit: NASA/JPL-Caltech)
- Warm colors in the infrared images (red, orange, yellow) show areas with little cloud cover. Cold colors (blue, purple) show areas covered by clouds that have developed sufficiently to reach high, cold altitudes, creating strong thunderstorms. The darker the color, the colder and higher the clouds and the stronger the thunderstorms. In the microwave images, blue indicates areas of heavy rainfall beneath the coldest clouds.
- These images illustrate how, over a 36-hour period, Harvey became more organized (shown by its more circular shape and more-developed rain bands in the later images), intensified (shown by the growing area of blue and purple colors in the infrared) and moved northwest toward Texas. The microwave images show how the areas with rain have grown in area and intensity.
- Together, these two instruments give a detailed picture of the atmospheric conditions in and around a storm like Harvey. These observations are used by weather forecasters to predict how Harvey will move and change strength.
• July 12, 2017: An iceberg about the size of the state of Delaware split off from Antarctica's Larsen C ice shelf sometime between July 10 and July 12. The calving of the massive new iceberg was captured by MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Aqua satellite (Figure 38), and confirmed by the VIIRS (Visible Infrared Imaging Radiometer Suite) instrument on the joint NASA/NOAA Suomi National Polar-orbiting Partnership (Suomi-NPP) satellite. The final breakage was first reported by Project Midas, an Antarctic research project based in the United Kingdom. 27)
- Larsen C, a floating platform of glacial ice on the east side of the Antarctic Peninsula, is the fourth largest ice shelf ringing Earth's southernmost continent. In 2014, a crack that had been slowly growing into the ice shelf for decades suddenly started to spread northwards, creating the nascent iceberg. Now that the close to 5,800 km2 chunk of ice has broken away, the Larsen C shelf area has shrunk by approximately 10 percent.
- "The interesting thing is what happens next, how the remaining ice shelf responds," said Kelly Brunt, a glaciologist with NASA's Goddard Space Flight Center in Greenbelt, Maryland, and the University of Maryland in College Park. "Will the ice shelf weaken? Or possibly collapse, like its neighbors Larsen A and B? Will the glaciers behind the ice shelf accelerate and have a direct contribution to sea level rise? Or is this just a normal calving event?"
- Ice shelves fringe 75 percent of the Antarctic ice sheet. One way to assess the health of ice sheets is to look at their balance: when an ice sheet is in balance, the ice gained through snowfall equals the ice lost through melting and iceberg calving. Even relatively large calving events, where tabular ice chunks the size of Manhattan or bigger calve from the seaward front of the shelf, can be considered normal if the ice sheet is in overall balance. But sometimes ice sheets destabilize, either through the loss of a particularly big iceberg or through disintegration of an ice shelf, such as that of the Larsen A Ice Shelf in 1995 and the Larsen B Ice Shelf in 2002. When floating ice shelves disintegrate, they reduce the resistance to glacial flow and thus allow the grounded glaciers they were buttressing to significantly dump more ice into the ocean, raising sea levels.
- Scientists have monitored the progression of the rift throughout the last year were using data from the European Space Agency Sentinel-1 satellites and thermal imagery from NASA's Landsat-8 spacecraft. Over the next months and years, researchers will monitor the response of Larsen C, and the glaciers that flow into it, through the use of satellite imagery, airborne surveys, automated geophysical instruments and associated field work.
- In the case of this rift, scientists were worried about the possible loss of a pinning point that helped keep Larsen C stable. In a shallow part of the sea floor underneath the ice shelf, a bedrock protrusion, named the Bawden Ice Rise, has served as an anchor point for the floating shelf for many decades. Ultimately, the rift stopped short of separating from the protrusion.
- "The remaining 90 percent of the ice shelf continues to be held in place by two pinning points: the Bawden Ice Rise to the north of the rift and the Gipps Ice Rise to the south," said Chris Shuman, a glaciologist with Goddard and the University of Maryland at Baltimore County. "So I just don' see any near-term signs that this calving event is going to lead to the collapse of the Larsen C ice shelf. But we will be watching closely for signs of further changes across the area."
- The first available images of Larsen C are airborne photographs from the 1960s and an image from a US satellite captured in 1963. The rift that has produced the new iceberg was already identifiable in those pictures, along with a dozen other fractures. The crack remained dormant for decades, stuck in a section of the ice shelf called a suture zone, an area where glaciers flowing into the ice shelf come together. Suture zones are complex and more heterogeneous than the rest of the ice shelf, containing ice with different properties and mechanical strengths, and therefore play an important role in controlling the rate at which rifts grow. In 2014, however, this particular crack started to rapidly grow and traverse the suture zones, leaving scientists perplexed.
- "We don't currently know what changed in 2014 that allowed this rift to push through the suture zone and propagate into the main body of the ice shelf," said Dan McGrath, a glaciologist at Colorado State University who has been studying the Larsen C ice shelf since 2008. McGrath said the growth of the crack, given our current understanding, is not directly linked to climate change.
- "The Antarctic Peninsula has been one of the fastest warming places on the planet throughout the latter half of the 20th century. This warming has driven really profound environmental changes, including the collapse of Larsen A and B," McGrath said. "But with the rift on Larsen C, we haven't made a direct connection with the warming climate. Still, there are definitely mechanisms by which this rift could be linked to climate change, most notably through warmer ocean waters eating away at the base of the shelf."
- While the crack was growing, scientists had a hard time predicting when the nascent iceberg would break away. It's difficult because there are not enough measurements available on either the forces acting on the rift or the composition of the ice shelf. Further, other poorly observed external factors, such as temperatures, winds, waves and ocean currents, might play an important role in rift growth. Still, this event has provided an important opportunity for researchers to study how ice shelves fracture, with important implications for other ice shelves.
- The U.S. National Ice Center will monitor the trajectory of the new iceberg, which is likely to be named A-68. The currents around Antarctica generally dictate the path that the icebergs follow. In this case, the new berg is likely to follow a similar path to the icebergs produced by the collapse of Larsen B: north along the coast of the Peninsula, then northeast into the South Atlantic.
Figure 38: Thermal wavelength image of a large iceberg, which has calved off the Larsen C ice shelf. Darker colors are colder, and brighter colors are warmer, so the rift between the iceberg and the ice shelf appears as a thin line of slightly warmer area. Image from July 12, 2017, from the MODIS instrument on NASA's Aqua satellite (image credit: NASA Worldview)
Figure 39: Animated GIF image of the growth of the crack in the Larsen C ice shelf, from 2006 to 2017, as recorded by NASA/USGS Landsat satellites (image credit: NASA/USGS Landsat)
• June 25, 2017: Wildfires spread across southern Siberia in late June 2017. According to Russian state media, at least 27,000 hectares (270 km2) were burning in the Irkutsk Oblast region. Another 27,000 hectares burned in neighboring states and regions. More than 200 firefighters were sent to control the blazes. Dry lightning and human carelessness were cited as the causes of some of the fires. 28)
- On June 22, 2017, MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Aqua satellite acquired the first two natural-color images of fires near Lake Baikal and the Angara River (Figures 40 and 41). The next day, Aqua MODIS acquired the third image (Figure 42), which shows dense smoke plumes spreading northeast toward Yakutsk. Red outlines on each image are hot spots detected by MODIS where surface temperatures indicate the presence of fire.
- According to the science team of NASA's OMPS (Ozone Mapping and Profiler Suite) on the Suomi NPP satellite, the aerosol index reached 19 over the Lake Baikal/Irkutsk region, indicating very dense smoke at high altitudes. Researchers are investigating at least three possible pyrocumulus cloud formations in the area; such fire clouds can loft ash and particles high into the atmosphere.
Figure 40: On June 22, 2017, MODIS acquired this natural color image of fires near Lake Baikal and the Angara River (image credit: NASA Earth observatory, image by Jeff Schmaltz, story by Mike Carlowicz)
Figure 41: MODIS detail image of fires near Lake Baikal and the Angara River (image credit: NASA Earth observatory, image by Jeff Schmaltz, story by Mike Carlowicz)
Figure 42: Aqua MODIS image acquired on June 23, 2017, which shows dense smoke plumes spreading northeast toward Yakutsk (image credit: NASA Earth observatory, image by Jeff Schmaltz, story by Mike Carlowicz)
• June 11, 2017: Most summers, jewel-toned hues appear in the Black Sea. The turquoise swirls are not the brushstrokes of a painting; they indicate the presence of phytoplankton, which trace the flow of water currents and eddies. 29)
- On May 29, 2017, MODIS on NASA's Aqua satellite captured the data for this image of an ongoing phytoplankton bloom in the Black Sea. The image is a mosaic, composed from multiple satellite passes over the region.
- Phytoplankton are floating, microscopic organisms that make their own food from sunlight and dissolved nutrients. Here, ample water flow from rivers like the Danube and Dnieper carries nutrients to the Black Sea. In general, phytoplankton support fish, shellfish, and other marine organisms. But large, frequent blooms can lead to eutrophication—the loss of oxygen from the water—and end up suffocating marine life.
- One type of phytoplankton commonly found in the Black Sea are coccolithophores—microscopic plankton that are plated with white calcium carbonate. When aggregated in large numbers, these reflective plates are easily visible from space as bright, milky water.
- "The May ramp-up in reflectivity in the Black Sea, with peak brightness in June, seems consistent with results from other years," said Norman Kuring, an ocean scientist at NASA's Goddard Space Flight Center. Although Kuring does not study this region, the bloom this year is one of the brightest to catch his eye since 2012.
- Other types of phytoplankton can look much different in satellite imagery. "It's important to remember that not all phytoplankton blooms make the water brighter," Kuring said. "Diatoms, which also bloom in the Black Sea, tend to darken water more than they brighten it."
Figure 43: The Black Sea acquired with MODIS on Aqua on May 29, 2017 (image credit: NASA Earth Observatory, image by Norman Kuring, NASA's Ocean Biology Processing Group, story by Kathryn Hansen and Pola Lem)
• May 17, 2017: Since November 2015, temperatures in Alaska have been high—at times remarkably high. The seventeen-month warm streak ultimately came to an end in March 2017, a month that was frigid even by Alaskan standards. Several towns recorded air temperatures that month falling as low as -46º Celsius, according to news reports. 30)
- This series of maps (Figure 44) is based on data from AIRS (Atmospheric Infrared Sounder) on NASA's Aqua satellite. The measurements shown here represent the temperature of the "skin" (or top 1 mm) of the land surface during the daytime — including bare land, snow or ice cover, urban areas, and cropland or forest canopy.
- LSTs (Land Surface Temperatures) should not be confused with surface air temperature measurements that are given in a typical weather report. LSTs reflect the heating of the land surface by sunlight and they can sometimes be significantly different from air temperatures.
- The maps show LST anomalies for each month compared to the average conditions for that month between 2002-2016. Aside from Alaska's North Slope, much of the rest of the state faced land surface temperatures that ranged from a few degrees below normal to as much as 10°C below normal in March 2017.
- AIRS is a hyperspectral infrared sensor that makes observations sensitive to atmospheric and surface conditions at 2,378 separate wavelengths. In addition to detecting land surface temperatures, this allows the sensor to measure air temperatures from several heights in the atmosphere. This makes it possible for scientists to create detailed three-dimensional maps—or temperature profiles—that go from the surface to an altitude of 40 km up.
- The cold snap proved to be short-lived. In April 2017, temperatures in Alaska flipped and became unusually warm again.
Figure 44: Alaska LSTs observed by the AIRS instrument on NASA's Aqua satellite in the period November 2015 to March 2017 (image credit: NASA Earth Observatory, images by Jesse Allen using AIRS LST data provided by the AIRS Team)
• May 6, 2017: In May 2017, a cold front pushing across northern China spurred a major dust storm that darkened skies throughout the region. On May 3, 2017, MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Aqua satellite captured an image of several large plumes of dust streaming east from the Gobi Desert (Figure 45). The next day, VIIRS (Visible Infrared Imaging Radiometer Suite) on Suomi NPP captured an image (Figure 46) showing skies thick with dust across much of northeastern China. Notice that cyclonic atmospheric circulation had sucked dust into and above the clouds. 31)
- Air quality in several large cities in northern China deteriorated rapidly after the dust arrived. In Beijing, air quality sensors at the U.S. embassy in Beijing saw the AQI (Air Quality Index) rise from 95 (moderate) at 3:00 A.M. on May 4 to 503 (beyond hazardous) just three hours later. At noon on May 4, the AQI level in Beijing rose as high as 621. AQI values of 0 to 50 are considered healthy. Values between 300 and 500 are considered hazardous.
- Breathing significant amounts of dust can exacerbate both cardiovascular and respiratory disease. Dust storms can also transport certain types of fungal, bacterial, and viral pathogens.
Figure 45: MODIS image of a major dust storm in northern China acquired on May 3, 2017 (image credit: NASA Earth Observatory, image by Jeff Schmaltz, caption by Adam Voiland)
Figure 46: VIIRS image on Suomi NPP, acquired on May 4, 2017, showing skies thick with dust across much of northeastern China (image credit: NASA Earth Observatory, image by Jeff Schmaltz, caption by Adam Voiland)
• May 4, 2017: Accurate weather forecasts save lives. NASA's AIRS (Atmospheric Infrared Sounder ) instrument, launched on this date 15 years ago on NASA's Aqua satellite, significantly increased weather forecasting accuracy within a couple of years by providing extraordinary three-dimensional maps of clouds, air temperature and water vapor throughout the atmosphere's weather-making layer. Fifteen years later, AIRS continues to be a valuable asset for forecasters worldwide, sending 7 billion observations streaming into forecasting centers every day. 32)
Figure 47: A visualization of AIRS measurements of water vapor in a storm near Southern California. AIRS' 3D maps of the atmosphere improve weather forecasts worldwide (image credit: NASA)
- Besides contributing to better forecasts, AIRS maps greenhouse gases, tracks volcanic emissions and smoke from wildfires, measures noxious compounds like ammonia, and indicates regions that may be heading for a drought. Have you been wondering how the ozone hole over Antarctica is healing? AIRS observes that too.
- These benefits come because AIRS sees many more wavelengths of infrared radiation in the atmosphere, and makes vastly more observations per day, than the observing systems that were previously available. Before AIRS launched, weather balloons provided the most significant weather observations. Previous infrared satellite instruments observed using about two dozen broad "channels" that averaged many wavelengths together. This reduced their ability to detect important vertical structure. Traditional weather balloons produce only a few thousand soundings (atmospheric vertical profiles) of temperature and water vapor a day, almost entirely over land. AIRS observes 100 times more wavelengths than the earlier instruments and produces close to 3 million soundings a day, covering 85 percent of the globe.
- AIRS observes 2,378 wavelengths of heat radiation in the air below the satellite. "Having more wavelengths allows us to get finer vertical structure, and that gives us a much sharper picture of the atmosphere," explained AIRS Project Scientist Eric Fetzer of NASA/JPL in Pasadena, California. Weather occurs in the troposphere, 11 to 19 km. Most of the infrared radiation observed by AIRS also originates in the troposphere.
- AIRS was widely recognized as a great advance very quickly. Only three years after its launch, former NOAA Administrator Conrad Lautenbacher said AIRS provided "the most significant increase in forecast improvement [in our time] of any single instrument."
- In the Beginning: AIRS was the brainchild of NASA scientist Moustafa Chahine. In the 1960s, Chahine and colleagues first conceived the idea of improving weather forecasting by using a hyperspectral instrument — one that breaks infrared and visible radiation into hundreds or thousands of wavelength bands. He flew some experimental prototypes as early as the 1970s, but AIRS did not come to fruition until advances in miniaturization made it possible to build an instrument with the needed capability that wasn't too heavy and bulky to launch. Chahine, who died in 2011, became the first AIRS Science Team leader.
- The instrument was built by BAE Systems, now located in Nashua, New Hampshire, under the direction of JPL. It is one of six instruments flying on the Aqua satellite in the A-Train satellite constellation. With a planned mission life of five years, it is still going strong at 15 and is expected to last until Aqua runs out of fuel in 2022.
- The value of AIRS to weather forecasting was quantified in several experiments by forecasting centers worldwide. In particular, the ECMWF (European Centre for Medium Range Weather Forecasts) has investigated in detail the impact on forecasts of different observational systems. "ECMWF studies have shown that in many circumstances, AIRS is responsible for reducing forecast errors by more than 10 percent. This is the largest forecast improvement of any single satellite instrument of the 2000s," said Joao Teixeira of JPL, the AIRS Science Team leader.
- Seeing More than Weather: Scientists always knew that AIRS' measurements contained information beyond what meteorologists need for weather forecasting. The spectral wavelengths it sees include parts of the electromagnetic spectrum that are important for studying climate. Carbon dioxide and other atmospheric trace gases leave their signatures in the measurements. Chahine later commented, "The information is all there in the spectra. We just had to figure out how to extract it."
- In the mid- to late 2000s, the AIRS project team turned to that challenge. In 2008, under Chahine's leadership, they published the first-ever global satellite maps of carbon dioxide in the mid-troposphere. These measurements showed for the first time that the most important human-produced greenhouse gas was not evenly mixed throughout the global atmosphere, as researchers had thought, but varied by as much as 1 percent (2 to 4 molecules of carbon dioxide out of every million molecules of the atmosphere).
- Since then, more and more information has been extracted from the AIRS spectra. The team now also produces data sets for methane, carbon monoxide, ozone, sulfur dioxide and dust, an important influence on how much radiation reaches Earth from the sun and how much escapes from Earth to space. Researchers have used these new data sets, and also the original AIRS temperature, cloud and water data sets, for many discoveries. To name a few recent findings:
a) A 2015 study showed that AIRS' measurements of relative humidity near Earth's surface show promise in detecting the onset of drought almost two months ahead of other indicators.
b) In 2013, researchers used AIRS' data record to find 18 global hot spots for atmospheric gravity waves — up-and-down ripples that may form in the atmosphere above something that disturbs air flow, such as a thunderstorm updraft or a mountain range. This new record of where and when disturbances regularly create gravity waves is valuable for improving weather and climate forecasts.
c) Global warming increases the amount of water vapor in the atmosphere, which in turn warms the atmosphere even further. This kind of self-feeding process is called a positive feedback loop. Climate scientists had long theorized that this feedback might double the warming from increases in carbon dioxide. AIRS' temperature and humidity data allowed them to confirm this hypothesis for the first time.
- AIRS' Legacy: Due to its resounding success, AIRS is no longer one of a kind. "The mission has demonstrated a measurement approach that will be used by operational agencies for the foreseeable future," said AIRS Project Manager Tom Pagano of JPL. Already, there are three other hyperspectral sounders in orbit: the Cross-track Infrared Sounder (CrIS) on the NASA/NOAA Suomi National Polar-orbiting Partnership (Suomi-NPP), and two Infrared Atmospheric Sounding Interferometer (IASI) instruments on EUMETSAT's MetOp-A and -B satellites. Additional sounders are planned for launch into the 2030s.
- Together, these hyperspectral instruments will create a record of highly accurate measurements of our atmosphere that will be many decades long. That will add one more benefit to AIRS' legacy: the potential for improving understanding of the climate of today and the future.
• April 20, 2017: From space, the Strait of Gibraltar appears tiny compared to the continents it separates. At the strait's narrowest point, Africa stands just 14 km from Europe. But the narrow waterway is a complex environment that gives rise to striking phytoplankton blooms when conditions are right (Figure 48). 33)
- Water conditions and circulation near the strait produced a bloom with colorful tendrils visible in this image, acquired on March 8, 2017. The image is composed from data acquired with VIIRS (Visible Infrared Imaging Radiometer Suite) on Suomi NPP, and MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Aqua satellite. A series of processing steps were applied to highlight color differences and bring out the bloom's subtler features.
- The intricate swirls of phytoplankton trace the patterns of water flow, which in this region can become quite turbulent. For example, water moving east from the North Atlantic into the Mediterranean Sea has created turbulence in the form of internal waves. These waves—sometimes with heights up to 100 meters—occur primarily deep within the ocean, with just a mere crest poking through the surface. At the same time, water flowing west helps stir up water in the North Atlantic, including the Golfo de Cádiz.
- While most of the swirls of color are phytoplankton, ocean scientist Norman Kuring of NASA's Goddard Space Flight Center notes that some of the color near coastal areas could be due to sediment suspended in the water, particularly near the mouths of rivers. Some of the yellow-green plume near the Guadalquivir River, for example, could be due to CDOM (Colored Dissolved Organic Matter). "My guess is that there is less suspended sediment along the Iberian and African coastlines than you might expect to find in eastern U.S. coastal waters, which overlay a broader continental shelf than what is found around Iberia," Kuring said.
Figure 48: MODIS and VIIRS observations on Aqua and Suomi NPP, respectively, showing water conditions near the Strait of Gibraltar, acquired on March 8, 2017 (image credit: NASA Earth Observatory, image by Norman Kuring, text by Kathryn Hansen)
• March 16, 2017: The first global, long-term satellite study of airborne ammonia gas has revealed "hotspots" of the pollutant over four of the world's most productive agricultural regions. The results of the study, conducted using data from NASA's AIRS (Atmospheric Infrared Sounder) instrument on NASA's Aqua satellite, could inform the development of strategies to control pollution from ammonia and ammonia byproducts in Earth's agricultural areas (Figure 49). 34)
- A University of Maryland-led team discovered steadily increasing ammonia concentrations from 2002 to 2016 over agricultural centers in the United States, Europe, China and India. Increased concentrations of atmospheric ammonia are linked to poor air and water quality. The NASA-funded study, published March 16 in Geophysical Research Letters, describes probable causes for the observed increased airborne ammonia concentrations in each region. Although specifics vary between areas, the increases are broadly tied to crop fertilizers, livestock animal wastes, changes to atmospheric chemistry, and warming soils that retain less ammonia. 35)
- "Measuring ammonia from the ground is difficult, but the satellite-based method we have developed allows us to track ammonia efficiently and accurately, said Juying Warner, UoM (University of Maryland) associate research scientist in atmospheric and oceanic science. "We hope that our results will help guide better management of ammonia emissions."
- AIRS, in conjunction with the AMSU (Advanced Microwave Sounding Unit) also on Aqua, senses emitted infrared and microwave radiation from Earth to provide a 3D look at our planet's weather and climate. Working in tandem, the instruments make simultaneous observations down to Earth's surface, even in the presence of heavy clouds. With more than 2,000 channels sensing different regions of the atmosphere, the system creates a global, 3D map of atmospheric temperature and humidity, cloud amounts and heights, concentrations of selected greenhouse and other trace gases, and many other atmospheric phenomena.
- "AIRS wasn't designed to observe ammonia (NH3), but the instrument sensitivity and stability have allowed us to monitor ammonia trends," said AIRS Project Scientist Eric Fetzer of NASA/JPL (Jet Propulsion Laboratory), Pasadena, California. "The unexpected large ammonia increase is one example of rapid atmospheric changes from human activities that AIRS is observing."
- Gaseous ammonia is a natural part of Earth's nitrogen cycle, but excess ammonia is harmful to plants and reduces air and water quality. In the troposphere — the lowest, most dense part of the atmosphere where all weather takes place and where people live — ammonia gas reacts with nitric and sulfuric acids to form nitrate-containing particles. Those particles contribute to aerosol pollution that is damaging to human health. Ammonia gas can also fall back to Earth and enter lakes, streams and oceans, where it contributes to harmful algal blooms and "dead zones" with dangerously low oxygen levels.
- "Little ammonia comes from tailpipes or smokestacks. It's mainly agricultural, from fertilizer and animal husbandry," said co-author and University of Maryland professor Russell Dickerson. "It has a profound effect on air and water quality — and ecosystems."
- Each major agricultural region highlighted in the study experienced a slightly different combination of factors that correlate with increased ammonia in the air from 2002 to 2016. The United States, for example, has not experienced a dramatic increase in fertilizer use or major changes in fertilizer application practices. But the study authors found that successful legislation to reduce acid rain in the early 1990s most likely had the unintended effect of increasing gaseous ammonia. The acids that cause acid rain also scrub ammonia gas from the atmosphere, and so the sharp decrease in these acids in the atmosphere is the most plausible explanation for the increase in ammonia over the same time frame.
- Europe experienced the least dramatic increase in atmospheric ammonia of the major agricultural areas studied. The researchers suggest this is due in part to successful limits on ammonia-rich fertilizers and improved practices for treating animal waste. Much like the United States, a major potential cause for increased ammonia traces back to reductions in atmospheric acids that would normally remove ammonia from the atmosphere.
- "The decrease in acid rain is a good thing. Aerosol loading has plummeted — a substantial benefit to us all," Dickerson said. "But it has also increased gaseous ammonia loading, which we can see from space."
- In China, a complex interaction of factors is tied to increased atmospheric ammonia. The authors suggest efforts to limit sulfur dioxide — a key precursor of sulfuric acid, one of the acids that scrubs ammonia from the atmosphere — could be partially responsible. But China has also greatly expanded agricultural activities since 2002, widening its use of ammonia-containing fertilizers and increasing ammonia emissions from animal waste. Warming of agricultural soils, due at least in part to global climate change, could also contribute.
- "The increase in ammonia has spiked aerosol loading in China. This is a major contributor to the thick haze seen in Beijing during the winter, for example," Warner said. "Also, meat is becoming a more popular component of the Chinese diet. As people shift from a vegetarian to a meat-based diet, ammonia emissions will continue to go up."
- In India, a broad increase in fertilizer use coupled with large contributions from livestock waste have resulted in the world's highest concentrations of atmospheric ammonia. But the researchers note that ammonia concentrations have not increased nearly as quickly as over other regions. The study authors suggest that this is most likely due to increased emissions of acid rain precursors and, consequently, some increased scrubbing of ammonia from the atmosphere. This leads to increased levels of haze, a dangerous trend confirmed by other NASA satellite instruments, Dickerson said.
- In all regions, the researchers attributed some of the increase in atmospheric ammonia to climate change, reflected in warmer air and soil temperatures. Ammonia vaporizes more readily from warmer soil, so as the soils in each region have warmed year by year, their contributions to atmospheric ammonia have also increased since 2002. The study also ascribes some ammonia fluctuations to wildfires, but these events are sporadic and unpredictable. As such, the authors excluded wildfires in their current analysis.
- "This analysis has provided the first evidence for some processes we suspected were happening in the atmosphere for some time," Warner said. "We would like to incorporate data from other sources in future studies to build a clearer picture."
Figure 49: Global atmospheric ammonia trends measured from space from 2002 to 2016. The hot colors represent increases from a combination of increased fertilizer application, reduced scavenging by acid aerosols and climate warming. The cool colors show decreases due to reduced agricultural burning or fewer wildfires (image credit: Juying Warner and UoM study team, GRL)
• February 24, 2017: It is rare for satellites to get a clear view of the whole Antarctic Peninsula, the northernmost arm of the continent and one of the largest contributors to sea level rise during the past half-century. In the winter, polar darkness hides this rocky, ice-covered strip; in the summer, clouds usually block the view. 36)
- But every now and then, usually in January or February, there is enough of a break in the clouds to get a good glimpse. That is what happened on January 8, 2016, when MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Aqua satellite captured this remarkably clear view of the peninsula (Figure 50).
- The ice-covered and mountainous peninsula stretches 1,300 km into the Southern Ocean. Some geologists think that millions of years ago the mountains may have connected to the Andes. An arcing underwater ridge connects the tip of the peninsula with several small islands (South Georgia, South Sandwich, and South Orkney) then continues to Tierra del Fuego, the southernmost point of South America.
- As with most of Antarctica, the feature that dominates the peninsula and the ocean surrounding it is ice. There is ice on land: the glaciers and ice sheets. There are thick slabs of floating ice that fan out along the coasts: the ice shelves. There are blocky chunks of floating ice that break off, or calve, into the sea—icebergs. Finally, there is often a thin crust of sea ice that forms on the ocean surface in cold weather.
- Just a few percent of the peninsula's land area is ice-free, and in some places the ice is as much as 500 m thick. The rare exposed areas (brown) are mainly isolated crags and mountain peaks—nunataks—that poke up through the ice layer.
- In recent decades, weather stations have measured fluctuating temperatures on the Antarctic Peninsula. Between 1951 and 2000, temperatures rose by 2.8°C, faster than anywhere else in the world. However, air temperatures then began an equally rapid swing in the opposite direction, dropping by roughly 1°C between 2000 and 2014. Meanwhile, surrounding ocean temperatures have been warming since the 1990s, particularly on the western side of the peninsula opposite the Larsen C Ice Shelf.
- While changing air temperatures may have had some effects on the ice, scientists increasingly believe that warming waters have changed the peninsula's ice shelves and glaciers the most. Alison Cook and David Vaughan of the British Antarctic Survey analyzed satellite images and aerial photographs dating back to the 1960s and concluded that seven of the twelve ice shelves along the coasts had gotten smaller between the 1960s and 2010.
- Larsen A (3,736 km2 in the 1960s), Larsen B (11,958 km2 in the 1960s), and Wordie (1,917 km2 in the 1960s) have changed the most, losing much of their ice. Note that when this image was captured sea ice—not the thick ice of an ice shelf—was present in Wordie Bay. George VI had lost some ice, but it remained about 92 percent of the size it was in 1947. Larsen C was relatively stable in 2010, but it is now poised to calve an iceberg the size of Delaware. Larsen D, which expanded by 4 percent, was the only ice shelf that grew larger, according to Cook and Vaughan's analysis.
- A similar story played out on the glaciers. Of the 860 glaciers on the peninsula, Cook and Vaughan found that 90 percent of them had retreated between the time they were first photographed roughly a half-century ago and 2010. Of these, 30 glaciers lost more than 10 km2 of ice, 190 lost between 1 and 10 km2, and 558 lost 1 km2 or less. Eighty-two glaciers advanced, most by less than 1 kilometer.
- The Fleming, Hariot, and Prospect glaciers—which flow off the peninsula into Wordie Bay—retreated the most during that time period. Hektoria, Crane, and Jorum — glaciers that flow into the Larsen B embayment — also retreated significantly. All of these glaciers saw rates of ice loss accelerate significantly when adjacent ice shelves, which helped hold them in place, broke up.
Figure 50: The MODIS instrument on Aqua captured this image of the Antarctic Peninsula on January 8 , 2016 (image credit: NASA Earth Observatory, image by Jesse Allen, caption by Adam Voiland)
• January 3, 2017: It may not be obvious to the naked eye, but events on Earth's surface — such as a burning fire or a floating iceberg — can affect the development and shape of clouds in the sky. The connection stems from how these events influence the rise and fall of air masses. 37)
- In general, clouds form where the air is ascending. Air cools as it rises, and because cold air holds less water, it quickly saturates and reaches the point of condensation as it cools in the atmosphere. The most common way to get moist air masses to rise is to heat the ground with sunlight. But the energy to lift air can come from other sources too, such as from the heat of a volcano or a fire (Figure 51).
Figure 51: Energy from the Sun-warmed ground is not the only way to get air masses to lift, cool, and form clouds. That energy can also come from the heat of a volcano or, in this case, fire. NASA's Aqua satellite captured this image of a pyrocumulonimbus cloud on August 5, 2014, south of Yellowknife, Canada (image credit: NASA Earth Observatory, images by Joshua Stevens and Jeff Schmaltz, using MODIS data from LANCE/EOSDIS Rapid Response)
Legend to Figure 51: Pyrocumulonimbus and pyrocumulus clouds — sometimes called "fire clouds" — are tall, cauliflower-shaped clouds that show up in satellite imagery as opaque white patches hovering over darker smoke. With the exception of their fiery origin, pyrocumulus clouds are similar to cumulus clouds in structure. The image of Figure 51 is taken from the feature: "A Celebration of Clouds". 38)
- While cloud growth favors ascending air, the converse also applies. Clouds generally fail to form where the air is descending. On June 1, 2016, VIIRS (Visible Infrared Imaging Radiometer Suite) on the Suomi NPP satellite captured this image (Figure 52) of a void in the low stratus clouds over iceberg A-56 as it drifted in the South Atlantic Ocean (Ref. 37).
- The exact reason for the hole is somewhat of a mystery. It could have happened by chance, although imagery from the days before and after this date suggest something else was at work. Steve Palm, a research meteorologist at NASA/GSFC (Goddard Space Flight Center), thinks the iceberg could have disrupted the air flow or modified the atmosphere in such a way to cause the clouds nearby to dissipate. If an obstacle is large enough, it can divert the flow of low-level air around it. At the same time, air above and downstream of the obstacle converges and sinks.
- "The sinking motion warms and dries out the air, causing a hole in the clouds," Palm said. "It is a common phenomenon often caused by islands."
Figure 52: VIIRS on Suomi-NPP captured this image on June 1, 2016 (image credit: NASA Earth Observatory, images by Joshua Stevens and Jeff Schmaltz, caption by Kathryn Hansen)
• December 20, 2016: In the middle of most ocean basins, far from nutrient-laden coastal upwelling and river outflows, life is sparse. Few fish reside here, and even the smaller lifeforms like phytoplankton are few and far between. — Coral islands, however, buzz with aquatic activity. Particularly in the vast Pacific Ocean, it is as though these islands have a life-sustaining halo extending dozens of kilometers and invigorating otherwise barren waters. A recent study published in Nature Communications shows that coral reefs and atolls seem to provide enough nutrients to sustain biological hot spots far beyond their immediate vicinity. 39) 40) 41)
- Scientists have long known of the "island mass effect," (IME)—when the qualities of ecologically productive islands extend into nutrient-depleted waters. But they did not know just how prevalent the effect was, or just how much credit to give phytoplankton for injecting life into surrounding areas. The study found that the vast majority (more than 90 percent) of coral reef islands and atolls raise biological diversity in the ocean around them. In fact, there is an average of 86 percent more phytoplankton on the outer fringes of these reefs than would otherwise be expected.
- "There's been sort of a longstanding paradox in how island reef ecosystems are so productive when their surrounding environment isn't," said Jamison Gove, lead author of the paper and research oceanographer in NOAA's Ecosystems and Oceanography Division. The field of study is roughly 60 years old, "But this is the first research to show that IME is a ubiquitous phenomenon."
- The swath of green at the equator (Figure 53) is an area of ocean upwelling known as the equatorial cold tongue, and it brings colder, nutrient-rich water from the depths to the surface. At the northeastern tip of Australia, there is another thick lip of green. However, the strong signal here may be due in part to bottom reflectance in shallow waters, which appears similar to chlorophyll by satellites. (Authors accounted for reflectance in the study area.)
- In many ways, the island mass effect resembles larger ocean upwelling events. When ocean currents and waves encounter an island, they flow around it, and deep, nutrient-rich water is jolted upward in currents. This stirring of the water column fosters biological activity. Such hot spots (shown in green) appear around the majority of islands in the Pacific, indicating high chlorophyll values in these places.
- Activity around the Gilbert Islands stands out. The islands themselves are far smaller than the green splotches surrounding them. The abundance of phytoplankton indirectly indicates the presence of other aquatic life as well—including squid, small fish, and larger predators like tuna—that consume phytoplankton or each other.
- By extension, people rely on those microscopic plankton for their food, Gove said. "The more we understand productivity in these ecosystems, the more we can think about future changes and how these communities stand to benefit or not as the climate changes."
Figure 53: The image depicts sea surface chlorophyll in the Pacific Ocean between July 2002 and June 2012. The map was made using data acquired by the MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Aqua satellite. Green areas correlate to higher chlorophyll (in milligram/m3), an indication of blooming phytoplankton. Blue areas indicate lower concentrations of chlorophyll and phytoplankton (image credit: NASA Earth Observatory map by Joshua Stevens, using chlorophyll data courtesy of Jamison Gove/Pacific Islands Fisheries Science Center and Gove, Jamison M., et al. (2016), caption by Pola Lem)
• On December 12, 2016, the MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Aqua satellite captured this natural-color image of dust over the Arabian Sea. The vortex of clouds and dust is rotating in a direction dictated by Earth's rotation. In the Northern Hemisphere, this cyclonic rotation is counter-clockwise when looking down from space. 42)
- The dust arrived over the sea with a mass of warm desert air—a condition known to suppress cloud formation. It is possible that the warm, dry center of the vortex had not mixed much with the moist marine air surrounding it. The edges of the vortex may have mixed more with the marine air, giving rise to shallow, isolated cumulus clouds.
Figure 54: MODIS natural color image of dust over the Arabian Sea, acquired on Dec. 12, 2016 [image credit: Jeff Schmaltz, MODIS Rapid Response Team at NASA/GSFC, caption by Kathryn Hansen with image interpretation by Andrew Ackerman (NASA/GISS) and Toshihisa Matsui (NASA/GSFC)]
• November 1, 2016: There is more than one way for iron to get into the central Gulf of Alaska, but none rival the visual spectacle of wind-blown plumes of dust from from Alaska's Copper River Valley. MODIS (Moderate Resolution Imaging Spectroradiometer) on Aqua and Terra captured the image of Figure 55 in October 2016. 43)
- Much of the dust is comprised of "glacial flour" or "rock flour"—a silty powder with grains finer than sand. This iron- and feldspar-rich substance forms when glaciers grind against underlying bedrock. Winds tend to loft it in the fall when river levels are low and snow has not yet fallen.
- While coastal waters in this part of Alaska have relatively high levels of iron, the micronutrient tends to be in short supply in deeper waters in the middle of the Gulf of Alaska. Soluble iron is an essential nutrient in marine ecosystems because phytoplankton—which sit at the center of marine food webs—depend on it to develop. These floating microscopic plant-like organisms are eaten, in turn, by everything from zooplankton to whales. So an ocean without much phytoplankton is often an ocean without much life at all.
- Dust storms play a key role in fueling phytoplankton blooms by delivering iron to the Gulf of Alaska. Even a small addition of iron there can spur a bloom, explained Santiago Gassó, a scientist at NASA Goddard Space Flight Center who is monitoring the current dust storm.
- While Gassó and other scientists will be using satellites to keep an eye out for phytoplankton blooms in the coming days, there is no guarantee that they will see one. "It is early winter in Alaska, so there may not be enough phytoplankton still alive (or not yet dormant) to trigger a response," Gassó said. It is also possible that a bloom may occur, but that satellites will miss it because of cloud cover.
- While the relationship between iron and phytoplankton is understood in broad terms, there are many details about the process in the Gulf of Alaska that are still unknown. For instance, what happens to iron that does not get used quickly? It may remain near the surface all winter and promote phytoplankton blooms in the spring, when more light is available. Or it may just sink.
- To help clarify the role of dust storms, a small team of NASA-funded scientists, including Gassó, have been studying the area since 2011 with satellites and with ground-based air monitors on Middleton Island. The island sits right in the middle of many dust plumes streaming from the Copper River delta. "I don't think people realize that Middleton Island is one of the best places in the world to study the natural ocean fertilization by wind-blown dust," said Gassó.
Figure 55: MODIS images on NASA's Terra and Aqua satellites captured these images on October 23, 24, and 25, 2016 (image credit: NASA Earth Observatory, image by Jeff Schmalz)
• Sept. 24, 2016: In mid-September 2016, wildfires continued to burn in Siberia (Figure 56) amid what has been an active fire season for the region. These fires are the latest in an active fire season. In late June 2016, satellites showed wildfires between the Russian cities of Miryuga and Koyumba, roughly 160 km east of the current flames. 44)
- The map of Figure 57 shows the concentration of aerosols over Russia on September 18 as detected by the OMPS (Ozone Mapping Profiler Suite) on the Suomi-NPP satellite. High concentrations are represented with shades of deep red; the lowest concentrations are shades of light yellow.
- Other data revealed that smoke from the fires was lofted high into the atmosphere. On September 20, the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite, which can detect the altitude of ash clouds, indicated that the tops of the smoke plumes reached an altitude of 9 km.
- An image of the same region acquired a few days earlier shows the smoke moving toward the southwest near the town of Ust'-Kut, Russia. A smoky haze filled the sky, and flakes of ash from the fire fell over the town, according to a local news report. The report also noted that employees of the Eastern Siberia-Pacific Ocean oil pipeline (which passes through the area) had to be evacuated.
Figure 56: The natural-color image, acquired on Sept. 18, 2016 by the MODIS instrument on NASA's Aqua satellite, shows huge plumes of smoke streaming toward the northwest. Areas in red show where MODIS detected unusually warm temperatures associated with fire (image credit: NASA Earth Observatory, image by Jeff Schmaltz)
Figure 57: Aerosol concentrations over Russia acquired on Sept. 18, 2016 by the OMPS instrument on Suomi-NPP. High concentrations are represented with shades of deep red; the lowest concentrations are shades of light yellow (image credit: NASA Earth Observatory, image by Jeff Schmaltz)
• July 26, 2016: Like the Aral Sea (of Kazakhstan and Uzbekistan), Iran's salty Lake Urmia has shrunk rapidly during the past few decades. As it grows smaller, the lake grows saltier. And as it grows saltier, microscopic organisms are periodically turning the water striking shades of red and orange (Figure 58). 45)
- The color changes have become common in the spring and early summer due to seasonal precipitation and climate patterns. Spring is the wettest season in northwestern Iran, with rainfall usually peaking in April. Snow on nearby mountains within the watershed also melts in the spring. The combination of rain and snowmelt sends a surge of fresh water into Lake Urmia in April and May. By July, the influx of fresh water has tapered off and lake levels begin to drop.
- The fresh water in the spring drives salinity levels down, but the lake generally becomes saltier as summer heat and dryness take hold. That's when the microorganisms show their colors, too. Careful sampling of the water would be required to determine which organisms transformed the lake in 2016, but scientists say there are likely two main groups of organisms involved: a family of algae called Dunaliella and an archaic family of bacteria known as Halobacteriaceae.
- "Previous research suggests that Dunaliella salina is responsible for reddening of Lake Urmia," explained Mohammad Tourian, a scientist at the University of Stuttgart. "In the marine environment, Dunaliella salina appears green; however, in conditions of high salinity and light intensity, the microalgae turns red due to the production of protective carotenoids in the cells."
- Other scientists emphasize the role of Halobacteriaceae, a group of bacteria found in water that is saturated or nearly saturated with salt. These bacteria release a red pigment called bacteriorhodopsin that absorbs light and converts it into energy for the bacteria. When populations of the bacteria are large enough, they can stain bodies of water.
- Note that in July 2016, the color of the lake (and thus salinity levels) appeared to be relatively constant, despite the presence of a highway causeway. While there has been concern that the causeway would make it difficult for water to circulate between the northern and southern arms of the lake—as is the case in the Great Salt Lake of Utah—the effect in Lake Urmia is not nearly as noticeable. The images of Figure 59, captured by the Operational Land Imager (OLI) on Landsat-8 on April 20 and July 9, 2016, show part of the causeway before and after the lake's color changed.
- While Lake Urmia has shifted from green to red and back several times in recent years, trends suggest that a red Urmia could become increasingly common. Drought and intensive water diversion for agriculture has been limiting the amount of fresh water reaching the lake. "The lake volume has been decreasing at an alarming rate of 1.03 km3 per year," noted Tourian, who recently analyzed data from several satellites to track how Urmia has changed. "The results from satellite imagery revealed a loss of water extent at an average rate of 220 km2 per year, which indicates that the lake has lost about 70 percent of its surface area over the last 14 years."
Figure 58: The MODIS instrument on Aqua recently captured a transition in the color of Lake Urmia between April and July 2016. On April 23, (left image) the water was green; by July 18, it was the color of wine. The shoreline is encrusted with salt deposits and appears white. Note that the ring of salt is especially noticeable in July, when water levels were lower (image credit: NASA Earth Observatory, images by Joshua Stevens)
Figure 59: Detail image of Lake Urmia, captured with OLI (Operational Land Imager) of Landsat-8 on April 20 and July 9, 2016 (image credit: NASA Earth Observatory, images by Joshua Stevens using USGS data)
• June 18, 2016: Dust storms over the Red Sea are not uncommon. This sea, after all, is surrounded by deserts. But sometime atmospheric conditions and topography combine to produce a storm that appears extraordinary in satellite imagery (Figure 60). 46)
- Winds appear to be blowing east-northeast out of Africa. "Although we see transport from the wide coastal area, the plume is especially dense over the Tokar Delta," said Georgiy Stenchikov of King Abdullah University of Science and Technology of Thuwal, Saudi Arabia.
- Gaps in near-coastal mountain ranges become pathways through which winds can carry dust and sand from inland areas toward the sea. For example Tokar Gap—located about 50 km inland—funnels winds toward the southeast from June to September. These winds spread dust from the Tokar delta out over the Red Sea and toward the Arabian Peninsula.
- According to Stenchikov, the wind gusts that caused the dust outbreak on June 15 were due to a cold front moving southeast. The front was related to a cyclone centered near the Persian Gulf, and it caused turbulent mixing of air and a series of associated haboobs.
- Scientists have been studying the dust in this area for a number of reasons. In general, dust in cloud-free conditions reflects sunlight and causes radiative cooling of the land and atmosphere. But according to Stenchikov, the effects on the energy balance of the Red Sea have not been well quantified.
- In addition, dust generated over the coastal area is often deposited in the sea. This provides an important nutrient supply to the Red Sea, which otherwise has very low nutrient levels, particularly in its more northern reaches.
Figure 60: The MODIS instrument of NASA's Aqua satellite acquired this dust storm over the Red Sea on June 15, 2016 at 11:05 UTC (image credit: NASA Earth Observatory, image by Jeff Schmaltz)
• March 2016: For a chemical compound that shows up nearly everywhere on the planet, methane still surprises us. It is one of the most potent greenhouse gases, and yet the reasons for why and where it shows up are often a mystery. What we know for sure is that a lot more methane (CH4) has made its way into the atmosphere since the beginning of the Industrial Revolution. Less understood is why the ebb and flow of this gas has changed in recent decades. 47)
- One can find the odorless, transparent gas miles below Earth's surface and miles above it. Methane bubbles up from swamps and rivers, belches from volcanoes, rises from wildfires, and seeps from the guts of cows and termites (where is it made by microbes). Human settlements are awash with the gas. Methane leaks silently from natural gas and oil wells and pipelines, as well as coal mines. It stews in landfills, sewage treatment plants, and rice paddies.
- AIRS (Atmospheric Infrared Sounder) aboard NASA's Aqua satellite offers one spaceborne perspective on the methane in Earth's atmosphere. The map of Figure 61 shows global methane concentrations in January 2016 at a pressure of 400 hPa (hectopascal), or roughly 6 km above Earth's surface. Methane concentrations are higher in the northern hemisphere because both natural- and human-caused sources of methane are more abundant there. Since AIRS observed the methane fairly high in the atmosphere, winds may have transported plumes of gas considerable distances from their sources.
Figure 61: The methane data are from the AIRS (Atmospheric Infrared Sounder) on the Aqua mission acquired in the period January 1-31, 2016 and from in situ measurements (image credit: NASA Earth Observatory, Joshua Stephens)
• March 2, 2016: The Korean peninsula is an ideal laboratory for understanding air quality. Home to about 75 million people, the peninsula sits downwind from several major pollution sources (Figure 62), and also has a few of its own. 48)
- The peninsula lies a few hundred kilometers east of several large, industrialized cities in China that emit pollutants such as sulfur dioxide and nitrogen dioxide. Winds routinely send plumes of dust from the Taklimakan and Gobi deserts toward the Koreas. And outbreaks of wildfires and crop fires in China and Russia can produce plumes of smoke that make their way into Korean airspace. Meanwhile, the city of Seoul (population 10 million) is a major source of urban pollution. Crop fires are a seasonal occurrence in North Korea. As a result, the air Koreans breathe contains a complex and seasonally changing mixture of gases and particles that can pose problems for human health.
- To gain a better understanding of air pollution in this part of the world, NASA and the Republic of Korea are developing plans for a cooperative field study of air quality in May and June 2016. The KORUS-AQ (Korea U.S.–Air Quality study) will assess air quality across urban, rural, and coastal areas of South Korea using combined observations from aircraft, ground sites, ships, and satellites. The findings are crucial for the development of ground- and space-based instruments, as well as computer models that can provide more accurate air quality assessments for decision-makers.
- "KORUS-AQ is a step forward in an international effort to develop a global air quality observing system," said James Crawford, a lead U.S. scientist on the project from NASA's Langley Research Center. "Both of our countries will be launching geostationary satellites that will join other satellites in a system that includes surface networks, air quality models, and targeted airborne sampling."
- Key science goals include: developing a better understanding of the conditions affecting the vertical distribution of air pollutants; how that distribution relates to cloud cover; what factors govern ozone photochemistry and the formation of aerosols; and how well models represent real atmospheric composition over the Korean peninsula.
- NASA will work with South Korea's National Institute of Environmental Research using a King Air aircraft from Hanseo University, a NASA DC-8 flying laboratory, and a NASA Beechcraft UC-12B King Air. Five South Korean instruments will fly on the DC-8, and one NASA instrument will be onboard the Hanseo aircraft. — The KORUS-AQ team planned the field campaign for spring because April to June is when the Korean peninsula gets its strongest influx of pollution from upwind sources. 49)
Figure 62: On April 15, 2015, the MODIS instrument on Aqua acquired this image, which shows smoke from fires in China blowing south over the Korean peninsula (image credit: NASA, Jeff Schmalz)
• Feb. 23, 2016: The Aqua spacecraft and its sensor complement (AIRS, AMSU, CERES, MODIS) are operating nominally (in their 14th year on orbit) with a life expectancy into the early 2020s. 50)
• December 7, 2015: JAXA is reporting that it has ended the operation of the AMSR-E (Advanced Microwave Scanning Radiometer-EOS) on December 4, 2015. AMSR-E has been operated for over nine years as an onboard device installed on Aqua, after its launch on May 4, 2002. 51)
- On Oct. 4, 2011, the AMSR-E reached its limit to maintain the antenna rotation speed necessary for regular observations (40 rotations per minute), and the radiometer automatically halted its observation and rotation. Further operation of AMSR-E was suspended. JAXA prepared a recovery plan with NASA engineers, and the AMSR-E restarted its observations in a slow rotation mode (2 rpm) on December 4, 2012.
- Although the AMSR-E observation data in slow rotation mode limited to observe sparse areas, it was used for cross-calibration with the AMSR-2 (successor of the AMSR-E) onboard the GCOM-W (Global Change Observation Mission-Water) of JAXA since its launch on May 18, 2012, in order to produce and provide a consistent and long-term dataset between the AMSR-E and AMSR-2, by correcting their differences in sensor properties.
- Now, the AMSR-E instrument reached its limit to maintain the antenna rotation speed necessary for the slow rotation mode of 2 rpm and it automatically halted its observation and rotation on December 4, 2015. As of December, this marks just three years of simultaneous AMSR-E and AMSR-2 operation. Since the project obtained sufficient data necessary for cross-calibration, JAXA decided to complete operation of the AMSR-E at this time.
- The AMSR-2 on GCOM-W has been operating as the successor of the AMSR-E in the same orbit. The AMSR-2 continues the long-term, high-resolution observation of global water cycle variation by the AMSR-E and related operational utilization, which are new fields exploited by the AMSR-E. Moreover, the AMSR-2 contributes on an ongoing basis to both fields of practical application and water cycle/and climate variation research.
Table 1: AMSR-E achievements on Aqua
• November 2015: In late October 2015, a 3,726 m volcano on the Indonesian island of Lombok began erupting. In the days that followed, ash from Mount Rinjani blanketed towns and farmland across three Indonesian islands and shut down air traffic to a number of airports. The MODIS instrument of the NASA Aqua and Terra satellites acquired these natural-color images of the plume. Ash drifted westward from Lombok toward Bali and Java. A small segment of eastern Java's coast is visible to the southwest of Bali. 52)
Figure 63: The Aqua MODIS instrument captured this image of the eruption of Mount Rinjani, Indonesia on Nov. 4, 2015 (image credit: NASA, Jeff Schmaltz)
Table 2: Aqua status summary (as of November 5, 2015) 53)
• In June 2015, the NASA Earth Science Senior Review 2015 was submitted to Michael Freilich of NASA. A total of 10 NASA missions were evaluated in extended operations: Aqua, Aquarius, Aura, CALIPSO, CloudSat, EO-1, GRACE, OSTM (Jason-2), SORCE, and Terra. The Aqua missions was recommended to continue through FY 16-17 and FY 18-19. 54)
- The Aqua spacecraft is still going strong after 13 years, and four of its instruments (AIRS, AMSU, CERES, and MODIS) continue to collect valuable data about the atmosphere, oceans, land, and ice. The Panel ranked this mission as the first among those missions reviewed. Based upon Aqua's high quality climate data records, the continuity of this time series is critical for the scientific community, governmental agencies and the international operational user community. Therefore, the Panel found that Aqua mission should be continued as currently baselined.
• The image of Figure 64 was released on March 24, 2015 in NASA's Earth Observatory series. According to ocean color expert Menghua Wang of NOAA, The region of Bohai Sea, Yellow Sea, and East China is one of the most turbid and dynamic ocean areas in the world. 55)
Figure 64: The Yellow Sea, pictured here in an image acquired on February 24, 2015, by the MODIS instrument on NASA's Aqua satellite (image credit: NASA Earth Observatory)
Legend to Figure 64: In the image, the brown area along China's Subei Shoal is turbid water commonly seen in coastal regions. According to Wang, shallow water depths, tidal currents, and strong winter winds likely contributed to the mixing of sediment through the water. Some of the swirls in the image might be due to the Yellow Sea Warm Current, which intrudes into the Yellow Sea in wintertime. This branch of the Kuroshio Current changes the temperature of the sea surface and brings instability that could be the cause of the relatively dark swirls in the lower-middle part of the image.
• On Feb. 26, 2015, the MODIS instrument on NASA's Aqua satellite observed some of that dust starting a trans-Atlantic journey. In Figure 65, vast amounts of dust rise up from Senegal, Mauritania, and Gambia. The plumes are thick and brown, suggesting that he dust is still compact and that it probably arose close to the coast—not from a more distant location in the North African interior. Some of the dust also appears to be settling into the waters just offshore, adding to the darkening effect in the satellite view. A bit farther offshore, the water surface is brightened by sunglint, the reflection of sunlight directly back at the camera from a relatively smooth surface. 56)
Hundreds of millions of tons of sand and dust particles are lifted from North African deserts each year and carried across the Atlantic Ocean. So much dust is kicked up that the microscopic particles amass into sweeping tan plumes that are visible to satellites.
In a new paper published on February 24, 2015, scientists using a NASA satellite announced that they had quantified in three dimensions how much dust makes the trans-Atlantic journey from the Sahara Desert to South America. Scientists not only measured the volume of dust, but they also calculated how much phosphorus—remnant in Saharan sands from the desert's ancient past as a lake bed—gets carried from one of the planet's most desolate places to one of its most fertile. 57)
Figure 65: Thick dust plumes obscure Africa's coast in this MODIS image acquired on Feb. 26, 2015 (image credit: NASA Earth Observatory)
• August 5, 2014: Algae bloom on Lake Erie (Figure 66). For at least fifty years, phytoplankton and algae blooms have been a regular occurrence in summer on Lake Erie. The microscopic, floating plants generally start to flourish in June and July as the water warms and stratifies, and their numbers typically peak in August and September. But it's not every year that a bloom leads to the shutdown of water supplies in an American or Canadian city. 58)
The dominant organism in the Lake Erie bloom is Microcystis spp., a type of freshwater blue-green algae that produces a toxin harmful to humans. If consumed, Microcystis can cause numbness, nausea, dizziness, and vomiting and lead to liver damage. (In rare cases, it can be deadly.) On August 2, 2014, environmental monitors for Toledo and surrounding towns in northwestern Ohio determined that public water supplies had levels of microcystin toxin that were higher than recommended by the World Health Organization (1.0 parts per billion). They warned residents not to drink or cook with tap water; boiling is not effective against the toxin. Though the bloom has continued, treatment facilities have since added extra filtering steps (including activated carbon), and public water sources were declared safe again on August 4.
Figure 66: Algae bloom on Lake Erie acquired with the Aqua MODIS instrument on August 3, 2014 (image credit: NASA Earth Observatory)
• July 2, 2014: NASA's Earth Observatory series released two images of the Leeuwin Current, flowing south along Australia's western shore, depicting SST (Sea Surface Temperature) and Chlorophyll Concentration of the region (Figure 67). 59)
Figure 67: The two figures were acquired on June 6, 2014 with MODIS on Aqua and released on July 2, 2014 (image credit: NASA's Earth Observatory series).
Legend to Figure 67: The Leeuwin Current is an oddity, because it flows away from the equator to the pole. Though invisible to the naked eye, the warm current stands out in measurements of the temperature of the ocean's surface (SST), as shown in the left image acquired by the MODIS (Moderate Resolution Imaging Spectroradiometer) instrument on NASA's Aqua satellite on June 6, 2014. Warmer water is orange and pink, while cooler water is purple.
The current hugs the coast, curving south and then east with the coastline. It is the world's longest coastal current, extending 5,500 km from the North West Cape to the west coast of Tasmania—roughly equivalent to the distance between San Francisco and Miami.
The heat the current transfers to southern Australia moderates the climate, making it hospitable to marine species normally found much closer to the equator. Its warmth also encourages rain to form and fall over western Australia, saving it from the extreme dryness found on the southwestern shores of the other southern continents. Without the current, western Australia might resemble South America's Atacama desert or southern Africa's Namib desert.
While the current makes southern Australia hospitable, it normally turns the ocean into a desert. The warm water contains limited nutrients to sustain plant life, and it represses upwelling, so surface waters seldom get recharged with nutrients from the ocean floor. Without nutrients, few phytoplankton grow. Since plankton are the base of the food chain, only small populations of fish are able to live in the warm waters.
In the right image of ocean chlorophyll, however, the ocean is clearly in full bloom. Acquired on June 6, 2014, by the MODIS sensor on the Aqua satellite, the image shows high concentrations of chlorophyll in yellow and lower concentrations in blue. The highest concentrations are aligned with the warmest parts of the current.
If warm water represses phytoplankton growth, why are plankton growing so well here? The answer is related to the current's swirling flow. The Leeuwin Current is extremely prone to eddies and meanders. In the fall, the current intensifies, flowing faster. The stronger eddies stir the water, allowing nutrients to reach the surface and fueling plankton blooms. In the winter, the blooms continue due to cooler temperatures and storms that agitate the water.
• May 17, 2014: The 2014 wildfire season got off to a ferocious start in southern California and northwestern Mexico when record-breaking temperatures and powerful Santa Ana winds fueled at least nine fires between May 14–16. Cal Fire estimated that by the morning of May 16, more than 7,700 hectare had burned, and news reports said that more than 100,000 people were forced to evacuate at various points over the past few days. 60)
- The MODIS instrument on Aqua detected several fires in San Diego County on May 14, 2014 (Figure 68). MODIS also observed large fires burning in the Baja California region of Mexico. Red outlines indicate hot spots where the sensor detected unusually warm surface temperatures associated with fires. Winds blew thick plumes of smoke west over the Pacific Ocean.
- Drought has plagued the western United States—especially central and southern California—for months, priming vegetation for wildfires. By mid-May, the entire state was classified as being in some level of drought (ranging from severe to exceptional), according to the U.S. Drought Monitor. To break the drought, most of the state would need 9 to 15 inches (23 to 38 centimeters) of precipitation to fall in one month, Weather Underground meteorologist Jeff Masters estimated. That would amount to more than a half-year's worth of precipitation for most of the state.
Figure 68: Fires in the Southwestern United States and Northern Mexico, acquired by MODIS on the Aqua spacecraft on May 14, 2014 (image credit: NASA Earth Observatory)
Legend to Figure 68: Red outlines indicate hot spots where the satellite's MODIS sensor detected unusually warm surface temperatures associated with fires. Winds blew thick plumes of smoke west over the Pacific Ocean.
• On April 25, 2014, the MODIS instrument on Aqua observed dozens of fires burning in North Korea. Actively burning areas, detected by the thermal bands on MODIS, are outlined in red. Fields and grasslands appear light brown. Forests at lower elevations appear green; at higher elevations, forests are still brown at this time of year. Collectively, the fires produced enough smoke to send plumes of haze drifting east over the Sea of Japan. 61)
- Many fires appear in farming areas along rivers. While North Korea's best agricultural land is located on the coastal plain in the western part of the country, many people farm marginal land along rivers in the mountainous areas. They use fire to clear debris from last year's crops and to help fertilize the soil for the coming season.
- However, some of the fires were burning in heavily forested areas, suggesting that they might be wildfires. Drooping wires on aging power lines are a common cause of wildfires in North Korea, according to a report published in the Asia-Pacific Journal.
Figure 69: Actively burning areas, as viewed by NASA's Aqua satellite on April 25, 2014, are outlined in red. Fields and grasslands appear light brown. Forests at lower elevations appear green; at higher elevations, forests are still brown at this time of year (image credit: NASA Earth Observatory)
• NASA released Figure 70 on April 30, 2014 showing a MODIS image on the Aqua satellite. Off the coast of southwest Africa, ocean currents, winds, and the underwater shelf interact to create compelling biology and chemistry. Plant-like phytoplankton often bloom in the nutrient-rich surface waters, while bacteria on the seafloor consume decaying plant and animal matter and occasionally release gas that bubbles to the surface. 62)
Just off the coast of Namibia, the Benguela Current flows along the ocean surface. It moves north and west along the coast from South Africa and is enriched by iron and other nutrients from the Southern Ocean and from dust blowing off African coastal deserts. Easterly winds push surface waters offshore and promote upwelling near the coast, which brings up cold, nutrient-rich waters from the deeper ocean. These interactions can make the ocean come alive with color.
Near the shore, yellow-green features in the water suggest the presence of sulfur. Studies have described how bacteria in oxygen-depleted bottom waters consume organic matter and produce prodigious amounts of hydrogen sulfide. As that gas bubbles up into more oxygen-rich water, the sulfur precipitates out and floats near the surface. It can give off a potent rotten-egg smell and pose a toxic threat to fish.
Further offshore, milky green water may be a bloom of one or several species of phytoplankton. As countless microscopic, plant-like organisms consume sunlight and nutrients, they also consume oxygen. Oxygen depletion can sometimes become so complete that it creates a "dead zone" that can suffocate other marine species. At the same time, the oxygen-depleted waters help sulfur-producing bacteria to thrive.
Figure 70: Plankton and Sulfur in the Benguela Current; this MODIS image was acquired on April 10, 2014 (image credit: NASA Earth Observatory)
• Feb. 2014: The Great Lakes Region of North America is experiencing a bitter cold winter. The true color image of Figure 71 shows the mostly frozen state of the Great Lakes on Feb. 19, 2014. On that date, ice spanned 80.3% of the lakes, according to NOAA's Great Lakes Environmental Research Laboratory in Ann Arbor, Michigan. 63)
The ice reached an even greater extent on Feb. 13, when it covered about 88% of the Great Lakes – coverage not achieved since 1994, when ice spanned over 90 %. In addition to this year, ice has covered more than 80% of the lakes in only five other years since 1973. The average annual maximum ice extent in that time period is just over 50%. The smallest maximum ice cover occurred in 2002, when only 9.5% of the lakes froze over.
Figure 71: This image, acquired with MODIS on the Aqua satellite, shows the Great Lakes on Feb. 19, 2014, when ice covered 80.3% of the lakes (image credit: Jeff Schmaltz, LANCE/EOSDIS MODIS Rapid Response Team, NASA)
• The Aqua spacecraft and its payload (except for AMSR-E which operates in a reduced mode) are operating nominally in 2014.
Figure 72: The Aqua satellite acquired this natural-color satellite image of a plankton bloom on Dec. 30, 2013. The eddy is centered about 600 km off the coast of Australia in the southeastern Indian Ocean (image credit: NASA Earth Observatory) 64)
Legend to Figure 72: In this Aqua/MODIS image, an eddy is outlined by a milky green phytoplankton bloom. Eddies are masses of water that typically spin off of larger currents and rotate in whirlpool-like fashion. They can stretch for hundreds of kilometers and last for months.
While the northern latitudes are bathed in the dull colors and light of mid-winter, the waters of the southern hemisphere are alive with mid-summer blooms. The eddy is centered at roughly 40º South latitude and 120º East longitude, about 600 km off the coast of Australia in the southeastern Indian Ocean.
• Nov. 8, 2013: The typhoon Haiyan was located over the central Philippines and was quickly heading towards the west at 22 knots (25 mph) when Aqua observed the region. 65)
Figure 73: AIRS image of the super typhoon Haiyan acquired on Nov. 8, 2013 at 04:59 UTC (image credit: NASA/JPL)
Legend to Figure 73: The lowest temperatures, in dark purple, are associated with the high, cold cloud tops of powerful thunderstorms with heavy rainfall potential. The Philippine islands stretch from the center of the image to the northwest. Northern Indonesia is at the bottom of the image, and northeastern Malaysia is at the lower left of the image. Some of the Philippine regions being pounded by the storm, in the area with purple coloring, are the Visayas, Bicol, National Capital, Central Luzon, Calabarzon, Northern Mindanao, and Mimaropa regions.
• 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. 66)
- The Aqua mission is now 5 years into its extended mission of producing a wide array of measurements in support of addressing NASA's Earth Science mission both from the perspective of creating climate data records necessary to evaluate climate change and from the perspective of products needed to better understand fundamental Earth science processes. The Aqua mission has been extremely successful and produces a large number of critical products that are very widely used by scientists, government agencies and operational groups.
- The AMSR-E instrument, which suffered a major anomaly in 2011, now operates in a reduced mode that provides data for cross-calibration with other AMSR instruments. All other instruments on Aqua are still operating nominally and the spacecraft is in excellent health and has enough fuel to operate through 2022.
- Of the Aqua sensor complement, MODIS and AIRS are making extremely unique and popular measurements for science and operational applications. The continuity of these data products is highly desirable for the scientific community and the broader user community.
• In February 2013, Aqua is over four and a half years beyond its prime mission, and yet the spacecraft and four of its instruments continue to operate well. HSB (from Brazil) failed in February 2003, and AMSR-E (from Japan) ceased science operations much more recently, in October 2011. As of December 2012, AMSR-E is again turned on, but at a much slower rotation rate (2 rpm versus 40 rpm) than desired for science data. The AMSR-E data being collected now are largely intended for cross-calibration with data from the AMSR-2 instrument (launch on May 17, 2012) flown on Japan's GCOM-W (= Shizuku) mission. The MODIS, AIRS, CERES, and AMSU (all from the U.S.) instruments on Aqua continue to work well. It's projected that the mission could continue until 2022. 67)
The retrieved atmospheric parameters using the observations from AMSR-E on Aqua are used primarily in climate research as well as in atmospheric models used in weather forecasting. This JAXA instrument performed exceptionally well for more than three times its design lifetime. 68)
• In mid-August 2012, an intense wildfire broke out on the Greek island of Chios, sending a thick plume of smoke southward toward the island of Crete. 69)
Figure 74: MODIS on Aqua captured this natural-color image on August 18, 2012 (image credit: NASA)
Legend to Figure 74: The image shows part of the Aegean Sea dotted with many Greek islands between the mainlands of Greece and Turkey. Greece typically sees little rain between April and September and experiences some of its highest temperatures in late July and early August. Wildfires are fairly common in the hot, dry days of August.
• July 2012: Aqua is operational and has now exceeded 10 years of on-orbit operations. It has collected a wealth of data that have been used for a variety of scientific and practical purposes. Well over 2,000 scientific papers have been published using Aqua data. An example of the many Aqua results deals with the the global energy budget. 70)
Figure 75: Outgoing longwave radiation, March 18, 2011, as derived from Aqua CERES data (image credit: Tak Wong and the CERES Science Team)
Legend to Figure 75: CERES measurements allow the derivation of the solar radiation reflected from the Earth/atmosphere system back to space and the Earth's longwave radiation emitted to space. The CERES data from Aqua and Terra have been used with incoming solar radiation data from the TIM (Total Irradiance Monitor) on the SORCE (Solar Radiation and Climate Experiment) mission to calculate that the Earth has been accumulating energy at a rate of approximately 0.50 ± 0.43 Wm-2 over the course of the 10 year period 2001-2010. 71) This slight imbalance at the top of the atmosphere means that more energy is entering than leaving the Earth system, resulting in overall warming.
• In May 2012, Aqua marked its 10th year on-orbit, delivering unprecedented data about the Earth's climate, water cycle and much more. The mission demonstrates the considerable benefits of long-term, space-based environmental monitoring. 72) 73) 74)
Legend to Figure 76: A layer of stratocumulus clouds over the Pacific Ocean served as the backdrop for this rainbow-like optical phenomenon known as a glory. Glories generally appear as concentric rings of color in front of mist or fog. They form when water droplets within clouds scatter sunlight back toward a source of illumination (in this case the Sun). - Although glories may look similar to rainbows, the way light is scattered to produce them is different. Rainbows are formed by refraction and reflection; glories are formed by backward diffraction. The most vivid glories form when an observer looks down on thin clouds with droplets that are between 10 -30 µm in diameter. The brightest and most colorful glories also form when droplets are roughly the same size.
Another notable feature in this image are the swirling von Karman vortices that are visible to the right of the glory. The alternating double row of vortices form in the wake of an obstacle, in this instance the eastern Pacific island of Guadalupe, located ~ 240 km off the west coast of Mexico's Baja California peninsula.
• In early 2012, the Aqua spacecraft and its instruments (AIRS, AMSU, CERES and MODIS) are in nominal operation. - In June 2011, the NASA Earth Science Senior Review recommended an extension of the Aqua mission to 2015. 76)
• The AMSR-E instrument operations ended on October 4, 2011. The AMSR-E instrument of JAXA (built by Mitsubishi Electric Company) continued its operation for more than 9 years (design life of 3 years). However, since the end of August, 2011, a continuous increase of relatively large antenna rotation friction was detected twice; as a consequence, JAXA has been monitoring the condition. On October 4, 2011, the AMSR-E reached its limit to maintain the rotation speed necessary for regular observations (40 rpm), and the radiometer automatically halted its observations and rotation. Although, JAXA continued to analyze this problem, and take necessary measures to correct the situation in cooperation with NASA, the AMSR-E mission came to an end. The cause of the failure is most likely due to aging lubricant in the bearing mechanism. 77)
The good news is that AMSR2, a slightly modified and improved version of AMSR-E, will be launched in 2012 on JAXA's GCOM-W1 satellite, and will join Aqua and the other satellites in NASA's A-Train constellation of Earth observation satellites. - The Aqua project had hoped that AMSR-E would provide at least one year of data overlap with the new AMSR2 instrument on GCOM-W1. 78)
• The Aqua spacecraft and its payload are operating nominally in 2011 with five of the six original Earth-observing instruments still operating well (these are: AIRS, AMSU, AMSR-E, MODIS, and CERES). It now looks like there is a good chance that the mission can continue at least to 2020. 79)
Figure 77: MODIS image of phytoplankton bloom in the Barents Sea observed on August 14, 2011 (image credit: NASA)
Legend to Figure 77: Brilliant shades of blue and green explode across the Barents Sea in this natural-color image taken on August 14, 2011, by MODIS on the Aqua spacecraft. Phytoplankton are tiny, microscopic plant-like organisms, but when they get together and start growing they can cover hundreds of square kilometers and be easily visible in satellite images. When conditions are right, phytoplankton populations can grow explosively, a phenomenon known as a bloom. A bloom may last several weeks, but the life span of any individual phytoplankton is rarely more than a few days. The area in this image is immediately north of the Scandinavian peninsula. Blooms spanning hundreds or even thousands of kilometers occur across the North Atlantic and Arctic Oceans every year. 80)
• The Aqua spacecraft and its payload are operating nominally in 2010. The Aqua sensors contain much synergy with each other and with other sensors and satellite platforms (e.g. Terra), and global climate model simulations. Many of these synergies have been explored, resulting in improved accuracy of core and new bio and geophysical products, and new understanding of the environment. - NASA hopes to continue the Aqua mission until at least the NPP mission is going to be launched in late 2011.
• The prime mission of Aqua was completed in September 2008. Five of the original six Aqua instruments are still operational and in good health, and should continue to operate successfully over the next four years (FY10-FY13) of the proposed continuation and beyond. In 2009, Aqua has adequate propellant for at least eight more years of normal operations. 81)
Scientific accomplishments and current merits of the Aqua platform are excellent. These merits include data and discoveries from approximately 100 data products that address each of NASA's six interdisciplinary Earth science focus areas and 12 Applied Science Program Elements. The Aqua data are considered to be critical for the activities associated with the current or upcoming IPCC Working Group 1 Assessment Report 5 (AR5), 2009–2012, for regional to global climate change assessment and forecasting studies.
• Aqua is operating nominally in 2005. 82)
• The HSB (Humidity Sounder for Brazil) instrument of INPE ceased operating in February 2003.
• The AIRS instrument, the first high-spectral-resolution infrared sounder developed by NASA/JPL, has provided the most significant increase in forecast improvement in this time range of any other single instrument.
• Nominal Aqua mission operations began on September 1, 2002.
Sensor complement: (AIRS, AMSU/HSB, AMSR-E, CERES, MODIS)
Aqua has six Earth-observing instruments on board, collecting a variety of global data sets. 83)
Note: The descriptions of CERES and MODIS can be found under Terra.
Table 3: Overview of sensor complement on the Aqua spacecraft
AIRS (Atmospheric Infrared Sounder):
AIRS is a NASA/JPL instrument, PI: M. T. Chahine; prime contractor is BAE Systems (Infrared and Imaging Systems Division (LMIRIS) of BAE Systems, in Lexington, MA). AIRS, along with AMSU and HSB, is of HIRS and MSU heritage flown on the NOAA POES series. Objective: High-spectral-resolution measurement of global temperature/humidity profiles in the atmosphere in support of operational weather forecasting by NOAA. Measurement of the Earth's upwelling infrared radiances in the spectral range of 3.74 - 15.4 µm, simultaneously at 2378 frequencies (bands). Four visible wavelength channels are also present. 84) 85) 86) 87) 88) 89) 90)
Figure 78: Photo of the AIRS instrument (image credit: NASA)
The AIRS spectrometer is a pupil imaging, multi-aperture echelle grating design that utilizes a coarse 13 lines/mm grating at high orders (3-11) to disperse infrared energy across a series of detector arrays. The typical entrance slit of a spectrometer is subdivided into a series of eleven apertures, each of which is imaged onto the focal plane. The grating serves to spectrally disperse each image, which in turn is overlaid onto a HgCdTe detector array with each detector in the array viewing a unique wavelength by virtue of the grating dispersion. Rejection of overlapping grating orders and background photon suppression is provided by a series of IR bandpass filters located within the spectrometer and directly on the focal plane. Use of the grating in combination with the filter set provides a two-dimensional color map on the focal plane with a high degree of design flexibility in terms of color arrangement and spacing. Cooling of the spectrometer to 155 K is provided by a two stage passive radiator assembly with 10 Watt cooling capacity at 155 K.
Figure 79: Isometric view of the AIRS instrument (image credit: NASA/JPL)
Dispersed energy exiting the spectrometer is imaged onto a state-of-the-art hybrid PV/PC: HgCdTe focal plane assembly (FPA) consisting of a series of multi-linear arrays each associated with a specific entrance aperture. The assembly consists of 17 arrays arranged in 12 modules with each module individually optimized for wavelength and photon flux. The module set includes 10 photovoltaic (PV) modules covering the 3.7 - 13.7 µm region and 2 photoconductive (PC) modules for the 13.7 - 15.4 µm region. The more advanced PV modules include on-focal plane signal processing via a custom CMOS Readout IC (ROIC) specifically designed for AIRS temperature, photon flux and radiation conditions. The ROIC provides the first stage of signal integration at a 1.4 ms subsample rate, which are summed off focal plane in groups of 16 to meet full footprint dwell time requirements. The IR FPA provides simultaneous measurement of 2378 spectral samples across the 3.7 - 15.4 µm region with two samples per resolution element. Additionally, each PV sample is further divided by two in the cross-dispersed direction to provide increased yield and a measure of spectral redundancy. As a consequence, the IR FPA contains a total of 4482 active detectors. The complex FPA is packaged in a vacuum dewar maintained at the 155 K spectrometer operating temperature, with the IR FPA cooled to 58 K via a redundant, 1.5 W capacity Split Stirling pulse tube cryocooler.
Figure 80: Illustration of the FPA (Focal Plane Assembly), image credit: NASA/JPL)
Figure 81: The AIRS spectrometer assembly (image credit: NASA/JPL)
Figure 82: AIRS scan assembly (image credit: NASA/JPL)
Figure 83: Illustration of the cryocooler assembly (image credit: NASA/JPL)
The infrared region of 3.74-15.4 µm has a spectral resolution of 1200 (lambda/ delta lambda). The high spectral resolution permits the separation of unwanted spectral emissions and, in particular, provides spectrally clean "super windows," ideal for surface observations. - This is supplemented by a VNIR photometer of four bands in the range between 0.4 and 1.0 µm. The VNIR channels are used to discriminate between low-level clouds and different terrain and surface covers, including snow and ice. The AIRS infrared bands have an IFOV of 1.1º and FOV = ± 49.5º scanning capability perpendicular to the spacecraft ground track (swath width = 1650 km, 13.5 km horizontal resolution in nadir, 1 km vertical). It takes 22.41 ms for each footprint of 1.1º in diameter (or 13.5 km). Each IR scan produces 90 footprints across the flight track and takes 2.67 s (see Figure 84). The VNIR channels have a footprint of 0.185º or about 2.3 km on the ground, nine VNIR footprints are within a 40 km swath. The VNIR photometer is boresighted to the spectrometer to allow simultaneous VNIR observations.
The VNIR photometer uses optical filters to define the four spectral bands. It operates at ambient temperatures (293-300 K). Inflight calibration is performed during each scan period. In addition, AIRS uses four independent cold-space views.
The major data products derived from AIRS are atmospheric temperature profiles, humidity profiles (from channels in the 6.3 µm water vapor band and the 11 µm windows, sensitive to the water vapor continuum), and land skin surface temperature.
AIRS is flown on the Aqua satellite with two operational microwave sounders: NOAA's AMSU and Brazil's HSB (Humidity Sounder Brazil). Together, the three sensors constitute constitute a possible advanced operational sounding system for future NOAA missions - offering increased accuracy of short-term weather predictions, improved tracking of severe weather events like hurricanes, and advances in climate research.
Table 4: Overview of some AIRS parameters
Figure 84: Illustration of the AIRS scan geometry and coverage (image credit: NASA/JPL)
Some AIRS results in 2010:
The excellent sensitivity and stability of the AIRS instrument has recently allowed the AIRS team to successfully retrieve Carbon Dioxide (CO2) concentrations in the mid-troposphere (8-10 km) with a horizontal resolution of 100 km and an accuracy of better than 2 ppm. 91)
Originally designed to retrieve temperature and water vapor profiles for weather forecast improvement, the AIRS (Atmospheric Infrared Sounder) has become a valuable tool for the measurement and mapping of mid-tropospheric carbon dioxide concentrations. Several researchers have demonstrated the ability to retrieve mid-tropospheric CO2 from AIRS by different methods. The retrieval method selected for processing and distribution is called the method of "Vanishing Partial Derivatives" and results in over 15,000 CO2 retrievals per 24-hour period with global coverage and an accuracy better than 2 ppm.
The AIRS CO2 accuracy has been validated against a variety of mid-tropospheric aircraft measurements as well as upward looking interferometers (FTIR) from the ground.
Mid-tropospheric CO2 concentrations are an indicator for atmospheric transport and several interesting findings have resulted from analysis of the data.
- First is the non-uniformity of CO2, primarily caused by weather.
- Second is the ability to identify stratospheric-tropospheric exchange during a sudden stratospheric warming event.
- Third is the presence of a seasonally varying belt of enhanced CO2 concentrations in the Southern Hemisphere.
Figure 85: AIRS yields about 15,000 mid-tropospheric CO2 measurements per day (image credit: NASA/JPL)
Carbon dioxide turns out to be an excellent tracer gas since it does not react with other gases in the atmosphere. The project is finding that the AIRS mid-tropospheric CO2 is a good indicator of vertical motion in the atmosphere. It is a known fact that the majority of atmospheric CO2 is produced and absorbed near the surface and that there are no sources or sinks in the free troposphere. Thus elevated levels of mid-tropospheric CO2 are the result of airflow into the mid-troposphere from the near surface.
The most obvious finding from the AIRS retrievals is that the distribution of CO2 is not uniform as indicated in the models. Strong latitudinal and longitudinal gradients exist particularly over the large land masses in the Northern Hemisphere. This phenomenon is referred to as "CO2 weather". The large variability in atmospheric circulation due to convection and global and mesoscale transport is responsible for most of the variability seen in the AIRS data. This implies that the AIRS CO2 data will be extremely useful for validating global scale transport in GCMs (Global Circulation Models).
Figure 86: AIRS mid-tropospheric CO2 is a tracer for atmospheric motion particularly in the vertical direction. July, 2010 monthly average (image credit: NASA/JPL)
AMSU/HSB (Advanced Microwave Sounding Unit (NASA Instrument)/ (Humidity Sounder for Brazil), provided by INPE. Both instruments operate in conjunction.
AMSU was designed and developed by Aerojet of Azusa, CA (a GenCorp company). AMSU primarily provides temperature soundings, whereas HSB provides humidity soundings. AMSU is a 15-channel microwave radiometer. AMSU and HSB have a total of 19 channels, 15 are assigned to AMSU, each having a 3.3º beamwidth, and four are assigned to HSB, each having a beamwidth of 1.1º. AMSU comprises two separate units: AMSU-A1 (channels 3-15), and AMSU-A2 (channels 1 and 2). Channels 3 - 14 use the 50 to 60 GHz oxygen band to provide data for vertical temperature profiles up to 50 km. The "window" channels (1, 2, and 15) provide data to enhance the temperature sounding by correcting for surface emissivity, atmospheric liquid water, and total precipitable water. HSB channels 17 - 20 use the 183.3 GHz water vapor absorption line to provide data for the humidity profile. 92) 93)
AMSU-A1 measures temperature profiles from the surface up to 50 km in 15 channels. Temperature resolution: 0.25 - 1.2 K. The AMSU-A1 instrument has two 15 cm diameter antennas (reflectors with momentum compensation), each with a 3.3º nominal IFOV at the half power points or FWHM (Full width Half maximum). Each antenna provides a cross-track scan of ±49.5º from nadir with a total of 30 Earth views (scan positions) per scan line. The total scan period is eight seconds. The footprint (resolution) at nadir is 40 km. The swath width is approximately 1690 km. Internal calibration is performed with internal warm loads and cold space.
AMSU-A2 has a single 28 cm diameter antenna (reflector without momentum compensation) with a 3.3º nominal IFOV. All other instrument/observation parameters are the same as those of AMSU-A1.
AMSU parameters: mass = 91 kg (49 kg for AMSU-A1, 42 kg for AMSU-A2); power = 101 W; data rate = 2.0 kbit/s; thermal control by heater, central thermal bus, radiator; thermal operating range= 0-20º C.
Table 5: Spectral parameters of the AMSU-A and HSB instruments
Figure 87: View of AMSU-A1 (left) and AMSU-A2 (right), image credit: Aerojet
Table 6: Summary of AMSU instrument parameters
HSB (Humidity Sounder for Brazil):
HSB is an INPE-provided instrument of AMSU-B heritage (built by MMS (Matra Marconi Space) of Bristol, UK (now EADS Astrium Ltd) with participation of Equatorial Sistemas of Brazil), and sponsored by AEB (Brazilian Space Agency). HSB is a microwave radiometer with the objective to measure atmospheric radiation, to obtain atmospheric water vapor profile measurements and to detect precipitation under clouds with 13.5 km horizontal nadir resolution (humidity profiles for weather foresting). 94) 95) 96)
HSB is a four-channel self-calibrating instrument (passive sounder) providing a humidity profiling capability in the frequency range of 150 - 190 GHz, spanning the height from surface to about 42 km. The measured signals are also sensitive to a) liquid water in clouds (cloud liquid water content) and b) graupel and large water droplets in precipitating clouds (qualitative estimate of precipitation rate). HSB scans in the cross-track direction at a rate of 2.67 seconds in continuous mode. The instrument features a momentum-compensated scan mirror system. HSB is operated in combination with AMSU-A, they have a total of 19 channels: 15 are assigned to AMSU-A, each having a 3.3º beamwidth, and four assigned to HSB, each having a 1.1º beamwidth. The HSB receiver channels are configured to operate in DSB (Double Sideband).
The HSB collected valuable data for the first nine months of the mission but ceased operating in February 2003 (scanner anomaly).
Table 7: Specification of the HSB instrument
Figure 88: Photo of the HSB instrument (image credit: NASA)
AMSR-E (Advanced Microwave Scanning Radiometer-EOS):
AMSR-E is a JAXA/NASA cooperative instrument, of AMSR heritage, built by Mitsubishi Electronics Corporation (PIs: A. Shibata, R. W. Spencer). The objective is the measurement of geophysical parameters such as: cloud properties, radiative energy flux, precipitation, land surface wetness (moisture), sea ice, snow cover, sea surface temperature (SST), and sea surface wind fields. AMSR-E is a modified design of AMSR on ADEOS-II (Japan).
The AMSR-E instrument is a conically scanning total power passive microwave radiometer sensing microwave radiation (brightness temperatures) at 12 channels and 6 frequencies ranging from 6.9 to 89.0 GHz (6.925, 10.65, 18.7, 23.8, 36.5, and 89.0 GHz). Horizontally and vertically polarized radiation are measured separately at each frequency. 97) 98) 99)
AMSR-E consists of an offset parabolic reflector 1.6 m in diameter, fed by an array of six feedhorns. The reflector and feedhorn arrays are mounted on a drum which contains the radiometers, digital data subsystem, mechanical scanning subsystem, and power subsystem. The reflector/feed/drum assembly is rotated about the axis of the drum by a coaxially mounted bearing and power transfer assembly. All data, commands, timing and telemetry signals, and power pass through the assembly on slip ring connectors to the rotating assembly. The AMSR-E instrument has a mass of 314 kg, power = 350 W, a duty cycle of 100%, and an average data rate of 87.4 kbit/s.
Table 8: Performance parameters of AMSR-E
Figure 89: Schematic view of the AMSR-E instrument (image credit: NASA)
The AMSR-E instrument rotates continuously about an axis parallel to the local spacecraft vertical at 40 rpm. At an altitude of 705 km, it measures the upwelling scene brightness temperatures over an angular sector of ± 61º about the subsatellite track, resulting in a swath width of 1445 km. During a period of 1.5 seconds the S/C subsatellite point travels 10 km. Even though the IFOV for each channel is different, active scene measurements are recorded at equal intervals of 10 km (5 km for the 89 GHz channels) along the scan. The half cone angle at which the reflector is fixed is 47.4º which results in an Earth incidence angle of 55.0º.
Figure 90: Line drawing of the AMSR-E instrument (image credit: NASA)
Instrument calibration. The radiometer calibration accuracy budget, exclusive of antenna pattern correction effects, is composed of three major contributors: warm load reference error, cold load reference error, radiometer electronics nonlinearities and errors.
Some data products from AMSR-E are:
• Level 2A brightness temperatures
• Level 2 rainfall
• Level 3 rainfall
• Columnar cloud water over the oceans
• Columnar water vapor over the oceans
• Sea surface temperature (SST)
• Sea surface wind speed
• Sea ice concentration
• Sea ice temperature
• Snow depth on sea ice
• Snow-water equivalent on land
• Surface soil moisture
Figure 91: The Aqua spacecraft and instrument accommodations (image credit: NASA, JAXA)
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90) Stuart MacCallum, "The Atmospheric InfraRed Sounder," 2005, URL: http://xweb.geos.ed.ac.uk/~stuart/Presentations/stuart_firbush2005.pdf
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98) AMSR-E Data Users Handbook, 4th Edition, JAXA, March 2006, NCX-030021
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).