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Aqua Mission (EOS/PM-1)

Spacecraft   Launch    Mission Status    Sensor Complement    References

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).

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Figure 1: Illustration of the Aqua satellite (image credit: NASA)

Spacecraft:

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).

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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.

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Figure 3: Illustration of Aqua in the A-train (image credit: NASA)

Figure 4: Anintroduction to Aqua (video credit: NASA)

 


 

Mission status:

• November 18, 2019: Citizens of central Chile are accustomed to long spells of dry weather. But the past decade has brought an extreme drought that is remarkable even for a region with a semi-arid Mediterranean climate. 5)

- Central Chile, where most Chileans live, has received 30 percent less rainfall than normal over the past decade, a situation that scientists are referring to as "megadrought." With rainfall deficits of 80 to 90 percent, 2019 has been particularly dry.

- Landscapes that would normally be lush and green have withered. The map of Figure 5 depicts the NDVI (Normalized Difference Vegetation Index), a measure of the health and greenness of vegetation based on how much red and near-infrared light it reflects. Healthy vegetation with lots of chlorophyll reflects more near-infrared light and less visible light. The NDVI anomaly map above is based on data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite between September 5 and November 5, 2019.

- The map contrasts vegetation health against the long-term average (2000–2010) for that period. Brown indicates vegetation that is less abundant and healthy than normal for this time of year. MODIS-based land cover data has been used to highlight areas that are snowy, icy, or have minimal vegetation. These areas appear gray. Green areas, mostly in valleys near glaciers and snow cover, have unusually abundant vegetation, likely because of increased melt and runoff from snow and glaciers.

- "An 80 percent deficit means that the semi-arid region north of Santiago has seen almost no water, as seen in the marked browning of the vegetation," said René D. Garreaud, a scientist at the University of Chile. "South of Santiago has received some rain—100 to 300 mm (4 to 12 inches). That is still not much, but it has been enough to keep the vegetation green."

- Garreaud and colleagues have detailed the progression and causes of the drought in several reports published in recent years. "We believe that such a long drought is the product of a combination of natural variability—the negative phase of the Pacific Decadal Oscillation—and human-caused climate change."

- As the drought persists, news reports present an increasingly grim picture. Ranchers have seen tens of thousands of animals die. Beehives are getting wiped out, and reservoirs are running low.

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Figure 5: The NDVI anomaly map above is based on data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua and Terra satellites between September 5 and November 5, 2019 (image credit: NASA Earth Observatory, image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview and topographic data from the SRTM ( Shuttle Radar Topography Mission), story by Adam Voiland)

• November 6, 2019: Hazy skies are a common occurrence over several states in northern India in November. After crops are harvested, winds often spread a river of smoke across much of the Indo-Gangetic Plain. 6)

- November 2019 was no exception. Smoke-filled skies led to hazardous air quality in many cities, hundreds of flight cancellations and delays, widespread school closures, and a two-week driving ban in Delhi.

- While industrial pollution and dust can contribute to the haze, most of it comes from crop-burning—especially in the states of Punjab and Haryana, where rice and wheat are widely grown. Burning typically peaks during the first week of November, a time when many farmers set fire to leftover rice stalks and straw after harvest, a practice known as stubble or paddy burning. The burning often coincides with falling temperatures and slow wind speeds, meteorological conditions that can lead to temperature inversions, which trap smoke in place.

- "The first week of November is typically the peak of burning," said Hiren Jethva, a Universities Space Research Association scientist based at NASA's Goddard Space Flight Center. "We will likely see fire activity and smoke intensity begin to diminish next week." He tracks the burning with several satellite sensors each year, noting that a particularly large rice crop in 2019 likely contributed to the severe burning.

- The fires release several types of gases into the atmosphere, including smog-forming carbon monoxide and nitrogen dioxide. They also release aerosols, such as black carbon and organic carbon, that contribute to elevated levels of PM2.5, which can cause health problems.

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Figure 6: In 2019, NASA Earth-observing satellites began to detect significant numbers of fires in mid October. By the end of the month, large numbers of fires were detected across much of the state of Punjab, as well as parts of northeastern Pakistan. MODIS on NASA's Aqua satellite captured this natural-color image on the afternoon of November 4, 2019, when a plume of smoke that had been emitted a few days earlier was sweeping through Delhi and Kanpur. The haze had pushed levels of fine particulate matter (PM2.5) to hazardous levels in Delhi, according to data collected at the U.S. Embassy (image credit: NASA Earth Observatory, image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview, story by Adam Voiland)

• October 28, 2019: From above, rivers that flow into the Bay of Fundy look a bit different than most. Their waters are often chocolate-colored, swirling with eddies, and bordered by red dunes and sandbars. 7)

- Sediment-rich waters are a common sight in the Bay of Fundy. With a tidal range up to 12 meters (38 feet), the funnel-shaped bay has the highest observed tides in the world. For comparison, most of the U.S. coast has a tidal range of 1 to 2 meters (3 to 6 feet).

- The geometry of the bay causes tidal resonance, which plays a key role in elevating tides. The bay is just the right width and depth for water to slosh back and forth at a frequency—every 12 or 13 hours—that matches the natural frequency of high tides, which are driven by the gravitational pull of the Moon and Sun on Earth. In addition, the position and configuration of continents in the Northern Hemisphere contributes to the high tides. Since North America, Europe, and Asia are pressed closer together than the continents in the Southern Hemisphere, water gets "constricted" in the Northern Hemisphere in a way that slightly amplifies tides.

- Since the Bay of Fundy becomes shallower and narrower, incoming tidal flows get forced especially high as water piles up behind mudflats at the mouth of the bay. Once water pushes past this obstacle, it rushes into the narrow valleys and collides with river water flowing in the opposite direction, producing waves and rapids that move opposite of the rivers' natural flow.

- The huge volumes of water rushing into Bay of Fundy's feeder rivers can create quite a spectacle, with surges of water that rush upstream at roughly 15 km (9 miles) per hour. They make a roaring sound reminiscent of an oncoming train. These tidal bores often have leading waves as high as 1 meter (3 feet), large enough for rafting and surfing.

- As for the colors, rivers in Nova Scotia and New Brunswick flow through soft red Triassic-era sandstone that easily erodes. The sediment and the regular churning of incoming and outgoing tides and tidal bores keeps the bay and rivers perpetually muddy.

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Figure 7: High tides in the funnel-shaped bay are anything but a bore when they collide with river water flowing in the opposite direction. On the afternoon of 20 October 2019, the MODIS instrument on NASA's Aqua satellite captured this image of sediment-rich water in the Bay of Fundy, the Shubenacadie River, and other nearby waterways in far eastern Canada. On land, fall weather had transformed the foliage of hardwoods and other deciduous trees and shrubs ( image credit: NASA Earth Observatory, image by Joshua Stevens, using data from the Level 1 and Atmospheres Active Distribution System (LAADS) and Land Atmosphere Near real-time Capability for EOS (LANCE). Story by Adam Voiland)

• October 25, 2019: Astronauts often return to Earth with a renewed appreciation for the complexity and beauty of our planet, a phenomenon sometimes called the overview effect. While most of us will never be lucky enough to see our home from space, natural-color imagery collected by Earth-observing satellites offers the next best thing. 8)

- The common thread connecting the dust and the curving clouds was a powerful thunderstorm churning over the Pilbara region of Western Australia. As a jet of cool air funneled out from the storm and hit a mass of warm air on the unusually hot day, it created a ripple-like disturbance—an atmospheric gravity wave. It also stirred up fierce winds that pushed a large dust plume northwest over the Indian Ocean. With enough moisture in the air to form bands of clouds, the normally invisible outlines of the gravity wave became visible.

- Down in the sea, other types of environmental dramas played out. Tendrils of phytoplankton, possibly Trichodesmium, drifted in currents north of Barrow Island. The nitrogen-fixing cyanobacteria, sometimes called "sea sawdust," play a key role in the nitrogen and carbon cycle.

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Figure 8: The interplay of a thunderstorm, dust, clouds, and gravity waves came together to create this scene. This natural-color image shows an intricate push-and-pull that recently played out between weather systems, clouds, and dust off the coast of Western Australia. The MODIS instrument on NASA's Aqua satellite acquired the image on October 21, 2019 (image credit: NASA Earth Observatory, image by Joshua Stevens, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Story by Adam Voiland)

• October 23, 2019: When you hear the word "drought", lack of rain probably comes to mind. But it is not only lack of rain that has put farmers in the U.S. Southeast in the grips of a damaging drought this fall. 9)

- Bouts of unusually warm temperatures, lots of sun, low humidity, and windy conditions can also come together to dry out soil surprisingly quickly, explained Christopher Hain, a scientist at NASA's Marshall Space Flight Center in northern Alabama. So quickly, in fact, meteorologists have coined a term—flash drought—to describe these fast-moving events.

- A stubborn ridge of high-pressure air hung over the Southeast for several weeks in September, bringing record-breaking temperatures, dry air, and very little rain. "We had a wet spring in the Southeast, so we went from no drought to severe drought within about four weeks," said Hain. "I'm hearing about farmers losing cotton, hay, and other forage crops. We are even seeing trees browning in certain areas."

- Other categories of drought can take much longer to develop. For instance, hydrological drought—like the one that made news in California in recent years—are defined by drops in groundwater levels, reservoirs, and stream flow that tend to span several months or years.

- Figures 9 and 10 show Evaporative Stress Index (ESI) data, a drought indicator based on observations of land surface temperatures from NOAA (National Oceanic and Atmospheric Administration) geostationary satellites and on observations of leaf area index from NASA's Terra and Aqua satellites and the VIIRS (Visible Infrared Imaging Radiometer Suite) on Suomi NPP. The combination makes it possible to gauge evapotranspiration—how much water is evaporating from the land surface and from the leaves of plants.

- "One of the issues with flash droughts is that they come on so quickly that they can get overlooked by policies intended to help farmers weather drought," said Hain, noting, that eligibility for some crop insurance can be tied to metrics other than the Evaporative Stress Index that don't always capture the onset of flash droughts.

- Other flash droughts that have had major impacts on farmers occurred in the central United States in 2012, in the Southeast in 2016, and in the Northern High Plains in 2017.

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Figure 9: After a wet spring, a quick-onset drought has parched fields. This map highlights the conditions between July 16 and August 13, before the flash drought. (image credit: NASA Earth Observatory, image by Lauren Dauphin using ESI (Evaporative Stress Index) data provided by Christopher Hain. Story by Adam Voiland)

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Figure 10: This map highlights the rapid onset of drought conditions (brown), shown in the period between September 10 and October 8, the peak of the drought. Rainstorms in recent weeks have lessened drought conditions somewhat (image credit: NASA Earth Observatory, image by Lauren Dauphin using ESI data)

• October 8, 2019: India's 2019 monsoon season has been one of the most unusual in recent decades. From June to September 2019, India received the highest amount of monsoonal rain in 25 years of records. According to the India Meteorological Department, those rains are not expected to retreat until at least October 10, which would be the latest withdrawal of the monsoon in the country's recorded history. 10)

- The monsoon usually accounts for around 70 percent of India's annual rainfall, but the surplus this year has caused major hardship. According to local media, floods this year have displaced or injured at least 2.5 million people in 22 states and killed several thousand.

- The most recently affected area is the state of Bihar in eastern India. In just a few days in late September, extreme rainfall covered many areas with knee-deep water. The images above show the flooding around the Ganges River in Bihar.

- The monsoon season started slow. In June 2019, much of India endured major heatwaves related to sparse spring rainfall and a late arrival of monsoon rains. By August and September, however, many regions were experiencing above average rain. In total, a national average of 97 cm of rain fell this year from June 1 to September 30, which is 110 percent of the norm and the most since 1994. (Average annual rainfall from 1951–2000 was 88 cm. It is important to note that while many portions of India have received a lot of rain, some regions have actually experienced a rainfall deficit.

- Much of the rain in 2019 was caused by an increased number of low-pressure systems. News reports state that the country experienced more extreme rainfall events this year compared to last year. Scientists believe the increased rain events could be associated with a phenomenon known as the Indian Ocean Dipole, when the western and eastern parts of the Indian Ocean are different temperatures. When the western portion is warmer than the eastern portion (as it was this summer), the region experiences a stronger monsoon rainfall.

- The India Meteorological Department predicts the monsoon will start withdrawing about a month later than usual. Researchers attribute the delay to unusual patterns in the Intertropical Convergence Zone (ITCZ), a region of weather centered around the equator where trade winds from the northern and southern hemispheres meet. Usually by September 1, temperatures decrease and the ITCZ moves south of India. However, temperatures have remained warm in the northern hemisphere, and ITCZ weather patterns have lingered longer than normal.

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Figure 11: This image was acquired with MODIS on NASA's Aqua satellite on 7 October 2019 (image credit: NASA Earth Observatory, image by Joshua Stevens, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Story by Kasha Patel)

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Figure 12: This image was acquired with MODIS on NASA's Aqua satellite on 2 October 2019 (image credit: NASA Earth Observatory, image by Joshua Stevens, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Story by Kasha Patel)

• October 7, 2019: Mariners have long noticed that the sea sometimes sparkles at night with an ethereal blue glow, especially after boats, waves, or even swimmers disturb the water. 11)

- Single-celled organisms known as Noctiluca scintillans—a type of dinoflagellate phytoplankton—is responsible for the glow. But despite the beauty of these "blue tear" blooms, when these bioluminescent organisms aggregate or grow into very high concentrations, they can form massive "red tides" that can harm marine life and create dead zones.

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Figure 13: This natural-color MODIS image on Aqua shows an example of a Noctiluca scintillans bloom near the mouth of the Yangtze River on May 18, 2017. MODIS can detect the blooms because this type of phytoplankton absorbs more blue light and scatters more red light than other ocean microorganisms. Since Noctiluca scintillans also scatters a significant amount of near-infrared light, the researchers were also able to identify blooms by analyzing false-color images that incorporate near-infrared observations (image credit: NASA Earth Observatory, image by Joshua Stevens, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Story by Adam Voiland)

- Scientists typically study such blooms by boat, but their vast size makes it difficult to map their full extent. However, scientists now have a powerful tool—satellite monitoring—to help them keep an eye on red Noctiluca scintillans blooms found in the East China Sea. In a study published in Geophysical Research Letters, a team of researchers described how they developed a technique to find and analyze blooms from a set of nearly 1,000 images taken between 2000 and 2017 by satellites and the International Space Station (ISS). Most of the data came from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra and Aqua satellites; some come from the Hyperspectral Imager for the Coastal Ocean (HICO) on the ISS.

- Since MODIS has collected daily images of the region for nearly two decades, the researchers were able to detect seasonal and interannual variations in the location and size of blooms. Noctiluca populations typically peaked between April and August and were usually found in coastal waters, near river mouths or deltas. Occasionally blooms drifted as far as 300 km offshore.

- The size and duration of the blooms varied from year to year, but there was a trend toward larger and longer-lasting blooms. In 2017, there was an especially long-lasting bloom that persisted from mid-April to mid-July. There were fewer blooms in the early 2000s, likely because construction of the Three Gorges Dam reduced the flow of nutrients down the Yangtze River.

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Figure 14: . The long-exposure photograph of 26 February 2007 shows the luminous glow the phytoplankton can produce (image credit: NASA Earth Observatory, photograph by Bruce Anderson (University of Stellenbosch). Story by Adam Voiland)

• October 4, 2019: The last time a major iceberg calved from East Antarctica's Amery Ice Shelf, there were no satellites poised to document the event. Scientists in the 1960s relied on aircraft, ships, and land-based studies to survey the ice shelf and its progeny. Now, more than half a century later, satellites have captured riveting space-based views as another huge berg has broken away from the shelf. 12)

Figure 15: The ice shelf in East Antarctica has spawned its first major iceberg in more than half a century. The animation is composed of images from the MODIS instruments on NASA's Aqua and Terra satellites; it shows the iceberg on six relatively cloud-free days between September 13 and October 2, 2019. The iceberg, named D-28, measures 1636 km2. For comparison, that's about the same area spanned by the city of Houston (image credit: NASA Earth Observatory image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Story by Kathryn Hansen)

- For ice shelves and glaciers that reach the ocean, calving is part of the natural cycle of advance and retreat. Compared to melting, the fastest way for glaciers to lose mass to the ocean is through rifting and the subsequent calving of icebergs. But there are still plenty of unknowns about how ice shelves and icebergs work. How do factors like waves, winds, melting from the shelf's underside, and even the structure of the ice, contribute to a calving event?

- Scientists working to answer these questions face a basic challenge: calving events are hard to observe. They happen infrequently and in remote locations. And if you try to make observations from the surface, there's the hazard of getting too close to an event with such explosive energy.

- Walker, Fricker, and Bassis originally focused on an area of ice called the "loose tooth." You can see this segment in the September 13 image of Figure 16; it appears to have a tenuous connection to the shelf, given its location between two large rifts. But the scientists eventually moved their attention west of the "loose tooth," where one of the rifts had picked up speed. They described their findings in a 2015 paper in the Journal of Glaciology.

- "So, we thought, maybe this side will go first," Walker said, which is exactly what happened when D-28 broke away. "It's still quite surprising how fast it went, though; the three of us have been looking at it often—most recently in April 2019—and we didn't foresee that it would be gone by October."

- The latest calving event provides more observations for the researchers to study. Analysis of D-28, combined with continued monitoring of the rifts, could help them better understand the factors leading to the creation of new icebergs, as well as what happens afterwards.

- "East Antarctica is a place often thought to be pretty stable and less affected by warming ocean and atmosphere trends," Walker said. "It will be interesting to compare calving events and see what this latest event tells us, and how that might be informative of what's starting to happen in East Antarctica."

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Figure 16: NASA snow and ice scientist Catherine Walker, and colleagues Helen Fricker (Scripps/UCSD) and Jeremy Bassis (University of Michigan), have taken another approach. They use satellite data to study the large systems of rifts that propagate across ice shelves as a precursor to calving. Over the past 20 years, rifts at Amery have been the most active—growing faster and more continuously than any other ice shelf around Antarctica. MODIS image as of 13 September 2019 (image credit: NASA Earth Observatory image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Story by Kathryn Hansen)

• September 14, 2019: Fire season in the Australian states of Queensland and New South Wales got off to an early and ugly start in September 2019. Fueled by a long and deepening drought, more than 100 fires burned in forest and bush areas near the southeast coasts, including some subtropical rainforests and eucalyptus forests that do not often see fire. 13)

- The Bushfire and Natural Hazards Cooperative Research Center reported in late August that the 2019-20 fire season—which usually peaks in October near the coast and later in the spring and summer inland—has the potential to be quite active. Conditions all year have been quite warm and dry across much of the nation. With some areas already facing water shortages, and with strong winds fanning the flames, firefighting has been difficult.

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Figure 17: Several years of dry conditions have set the stage for a fierce fire season in several southeastern states. On 12 September 2019, the MODIS instrument on NASA's Aqua satellite acquired this natural-color image of fires in the northeastern reaches of New South Wales. Strong westerly winds fanned the flames and carried smoke more than 100 km (NASA Earth Observatory, image by Lauren Dauphin and Joshua Stevens, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview and soil moisture data courtesy of JPL and the SMAP Science Team. Story by Michael Carlowicz)

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Figure 18: This map shows soil moisture anomalies, or how much the water content near the land surface was above or below the norm as of September 5-7, 2019. The measurements are derived from data collected by the Soil Moisture Active Passive (SMAP) mission, a NASA satellite dedicated to measuring the water content of soils. SMAP's radiometer can detect water in the top 5 cm of the ground. Scientists use that surface layer data in a hydrologic model to estimate how much water is present even deeper in the root zone, which is important for agriculture (image credit: NASA Earth Observatory images by Lauren Dauphin and Joshua Stevens, using soil moisture data courtesy of JPL and the SMAP Science Team. Story by Michael Carlowicz)

- According to the Australian Bureau of Meteorology (BOM), "August rainfall was below average over much of New South Wales, southern Queensland, northern and eastern Victoria, South Australia, and northern Tasmania," and conditions are not expected to improve anytime soon. Drier than normal conditions have persisted since the beginning of 2017 and, according to BOM, the past 32 months have been the driest on record for New South Wales—34 percent below average.

• August 27, 2019: With the fire season in the Amazon approaching its midpoint, scientists using NASA satellites to track fire activity have confirmed an increase in the number and intensity of fires in the Brazilian Amazon in 2019, making it the most active fire year in that region since 2010. 14)

- Fire activity in the Amazon varies considerably from year-to-year and month-to-month, driven by changes in economic conditions and climate. August 2019 stands out because it has brought a noticeable increase in large, intense, and persistent fires burning along major roads in the central Brazilian Amazon, explained Douglas Morton, chief of the Biospheric Sciences Laboratory at NASA's Goddard Space Flight Center. While drought has played a large role in exacerbating fires in the past, the timing and location of fire detections early in the 2019 dry season are more consistent with land clearing than with regional drought.

- "Satellites are often the first to detect fires burning in remote regions of the Amazon," Morton said. NASA's primary tool for fire detections since 2002 has been the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on the Terra and Aqua satellites.

- At this point in the fire season, MODIS active fire detections in 2019 are higher across the Brazilian Amazon than in any year since 2010. The state of Amazonas is on track for record fire activity in 2019.

- Morton noted that 2019 fire activity statistics distributed by NASA and Brazil's Instituto Nacional de Pesquisas Espaciais (INPE) are in agreement. "INPE also uses active fire data from NASA's MODIS sensors to monitor fire activity in the Brazilian Amazon," Morton said. "As a result, NASA and INPE have the same estimates of changes in recent fire activity. MODIS detections are higher in 2019 than at this time last year in all seven states that comprise the Brazilian Amazon."

- MODIS fire detections are analyzed by the Global Fire Emissions Database (GFED) project, which includes Morton and colleagues from NASA Goddard, the University of California, Irvine, and Vrije Universiteit Amsterdam. Over the years, the GFED team has processed 17 years of NASA satellite data to better understand the role of fire for changes in the Earth system. Their analysis of the southern Amazon includes parts of Brazil, Peru, and Bolivia that typically see fires between July and October. Their data plots are available online here.

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Figure 19: This map shows active fire detections in Brazil as observed by Aqua and Terra MODIS between August 15-22, 2019. The locations of the fires, shown in orange, have been overlain on nighttime imagery acquired by the VIIRS instrument on Suomi NPP. In these data, cities and towns appear white; forested areas appear black; and tropical savannas and woodland (known in Brazil as Cerrado) appear gray. Note that fire detections in the Brazilian states of Pará and Amazonas are concentrated in bands along the highways BR-163 and BR-230 (image credit: NASA Earth Observatory, image by Joshua Stevens, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview, Fire Information for Resource Management System (FIRMS) data from NASA EOSDIS, and data from the Global Fire Emissions Database (GFED). Story by Adam Voiland, with information from Douglas Morton)

• August 23, 2019: New data from NASA's Atmospheric Infrared Sounder (AIRS) instrument, aboard the Aqua satellite, shows the movement high in the atmosphere of carbon monoxide associated with fires in the Amazon region of Brazil. 15)

Figure 20: This time series shows carbon monoxide associated with fires from the Amazon region in Brazil from Aug. 8-22, 2019. Made with data collected from the AIRS instrument on NASA's Aqua satellite, the images map carbon monoxide at approximately 5,5 km altitude. Each "day" in the series is made by averaging three day's-worth of measurements (image credit: NASA/JPL-Caltech)

- Each "day" in the series is made by averaging three days' worth of measurements, a technique used to eliminate data gaps. Green indicates concentrations of carbon monoxide at approximately 100 parts per billion by volume (ppbv); yellow, at about 120 ppbv; and dark red, at about 160 ppbv. Local values can be significantly higher.

- A pollutant that can travel large distances, carbon monoxide can persist in the atmosphere for about a month. At the high altitude mapped in these images, the gas has little effect on the air we breathe; however, strong winds can carry it downward to where it can significantly impact air quality. Carbon monoxide 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. With more than 2,000 channels sensing different regions of the atmosphere, the instruments create a global, three-dimensional map of atmospheric temperature and humidity, cloud amounts and heights, greenhouse gas concentrations and many other atmospheric phenomena.

• August 21, 2019: The control of fire is a goal that may well be as old as humanity, but the systematic monitoring of fire on a global scale is a much newer capability. 16)

Figure 21: The animation shows the locations of actively burning fires on a monthly basis for nearly two decades. The maps are based on observations from the MODIS instrument on NASA's Terra satellite. The colors are based on a count of the number (not size) of fires observed within a 1,000 km2 area. White pixels show the high end of the count—as many as 30 fires in a 1,000 km2 area per day. Orange pixels show as many as 10 fires, while red areas show as few as 1 fire per day (video credit: NASA)

- In the 1910s, the U.S. Forest Service began building fire lookout towers on mountain peaks in order to detect distant fires. A few decades later, fire-spotting airplanes flew onto the scene. Then in the early 1980s, satellites began to map fires over large areas from the vantage point of space.

- Over time, researchers have built a rich and textured record of Earth's fire activity and are now able to analyze decadal trends. "The pace of discovery has increased dramatically during the satellite era," said James Randerson, a scientist at the University of California, Irvine. "Having high-quality, daily observations of fires available on a global scale has been critical."

Figure 22: The sequence highlights the rhythms—both natural and human-caused—in global fire activity. Bands of fire sweep across Eurasia, North America, and Southeast Asia as farmers clear and maintain fields in April and May. Summer brings new activity in boreal and temperate forests in North America and Eurasia due to lighting-triggered fires burning in remote areas. In the tropical forests of South America and equatorial Asia, fires flare up in August, September, and October as people make use of the dry season to clear rainforest and savanna, as well as stop trees and shrubs from encroaching on already cleared land. Few months pass in Australia without large numbers of fires burning somewhere on the continent's vast grasslands, savannas, and tropical forests (image credit: NASA Earth Observatory, image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Story by Adam Voiland)

- But it is Africa that is truly the fire continent. On an average day in August, the MODIS instrument on NASA's Aqua and Terra satellites detect 10,000 actively burning fires around the world—and 70% of them happen in Africa. Huge numbers of blazes spring up in the northern part of the continent in December and in January. A half year later, the burning has shifted south. Indeed, global fire emissions typically peak in August and September, coinciding with the main fire seasons of the Southern Hemisphere, particularly in Africa. (High activity in temperate and boreal forests in the Northern Hemisphere in the summer also contribute.)

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Figure 23: This satellite image shows smoke rising from the savanna of northern Zambia on August 29, 2018, around the time global emissions reach their maximum (image credit: NASA Earth Observatory, image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Story by Adam Voiland)

- Though Africa dominates in the sheer number of fires, fire seasons there are pretty consistent from year-to-year. The most variable fire seasons happen elsewhere, such as the tropical forests of South America and equatorial Asia. In these areas, the severity of fire season is often linked to cycles of El Niño and La Niña. The buildup of warm water in the eastern Pacific during an El Niño changes atmospheric patterns and reduces rainfall over many rainforests, allowing them to burn more easily and widely.

Figure 24: Watch as surface and subsurface ocean temperature anomalies in the Pacific show the rise and fall of an El Niño (video credit: NASAEarthObservatory, Published on Feb 14, 2017)

- Despite the vast quantities of carbon released by fires in savannas, grasslands, and boreal forests, research shows that fires in these biomes do not generally add carbon to the atmosphere in the long term. The regrowth of vegetation or the creation of charcoal typically recaptures all of the carbon within months or years. However, when fires permanently remove trees or burn through peat (a carbon-rich fuel that can take centuries to form), little carbon is recaptured and the atmosphere sees a net increase in CO2.

- That is why outbreaks of fire in countries with large amounts of peat, such as Indonesia, have an outsized effect on global climate. Fires in equatorial Asia account for just 0.6 percent of global burned area, yet the region accounts for 8 percent of carbon emissions and 23 percent of methane emissions.

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Figure 25: On October, 25, 2015, the EPIC (Earth Polychromatic Imaging Camera) aboard the DSCOVR satellite acquired an image of heavy smoke over Indonesia; El Niño was particularly active at the time (image credit: NASA Earth Observatory)

- One of the most interesting things researchers have discovered since MODIS began collecting measurements, noted Randerson, is a decrease in the total number of square kilometers burned each year. Between 2003 and 2019, that number has dropped by roughly 25 percent.

- As populations have increased in fire-prone regions of Africa, South America, and Central Asia, grasslands and savannas have become more developed and converted into farmland. As a result, long-standing habits of burning grasslands (to clear shrubs and land for cattle or other reasons) have decreased, explained NASA Goddard Space Flight scientist Niels Andela. And instead of using fire, people increasingly use machines to clear crops.

Figure 26: "There are really two separate trends," said Randerson. "Even as the global burned area number has declined because of what is happening in savannas, we are seeing a significant increase in the intensity and reach of fires in the western United States because of climate change"(image credit: NASA Earth Observatory)

- When researchers began using satellites to study the world's fires in the 1980s, they were just sorting out the basics of how to detect fires from space. Now after mining MODIS data for nearly two decades, scientists are looking ahead to other satellites and technologies that they hope will advance the study of fire in the coming years.

- A series of follow-on sensors called the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP and NOAA-20 satellites now make near-real time observations of emissions that are even more accurate than those from MODIS because of improved fire detections along the edge of the edges of images, noted Andela.

- Meanwhile, the launch of satellites with higher-resolution sensors is also helping. "The Landsat-8 and Sentinel satellites, in particular, are contributing to a revolution in our ability to measure the burned area of small grassland and forest fires," said Randerson. "And we are going to need additional detection capabilities in the coming years to track increasingly destructive mega fires during all times of day and night."

• July 16, 2019: There is nothing unusual about this mid-summer pop of color in the waters off of Iceland. July 2019 brought the latest display of a phytoplankton bloom that occurs every year in the North Atlantic Ocean. Yet we never tire of watching it. The blooms trace the day's patterns of surface water flow, and no two views are ever the same. 17)

- "The structure of the bloom clearly shows the influence of ocean circulation on the distribution and concentration of phytoplankton," said Michael Behrenfeld, a phytoplankton ecologist at Oregon State University.

- A bloom is essentially an abundance of phytoplankton—a plant-like organism that is important for carbon cycling and also could influence clouds and climate. They are also a critical part of the ocean's food chain and support Iceland's productive fisheries.

- Without water samples, it is not possible to say for sure what species are present. The bloom could contain diatoms, a microscopic form of algae with silica shells and plenty of the chlorophyll, which has a green pigment. They are one of the most common types of phytoplankton in the ocean. Or the bloom could contain coccolithophores, which are plated with white calcium carbonate that can give the ocean a milky hue.

- Whichever species is flourishing here, they are doing so right on time. The explosion of phytoplankton numbers, or "bloom," tends to happen first at lower latitudes. By spring and mid-summer, blooms become common at high latitudes of the North Atlantic.

- We see phytoplankton from space when they reach high concentrations at the ocean's surface, but they are still present earlier in the year at various depths. Research into the timing and cause of blooms in the North Atlantic have shown that populations start to increase as early as winter.

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Figure 27: July 2019 brought the latest display of a phytoplankton bloom that occurs every year in the North Atlantic Ocean. MODIS on NASA's Aqua satellite acquired the wide image of the bloom on 6 July 2019 (image credit: NASA Earth Observatory, images by Joshua Stevens, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Story by Kathryn Hansen)

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Figure 28: This image shows a detailed view on July 7, acquired with the Operational Land Imager (OLI) on Landsat 8 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Kathryn Hansen)

• July 12, 2019: NASA's AIRS (Atmospheric Infrared Sounder) aboard the Aqua satellite, captured imagery of Tropical Storm Barry in the Gulf of Mexico at about 2 p.m. local time on Friday afternoon. According to the National Hurricane Center, Barry is expected to make landfall over the Louisiana coast on Saturday, likely as a hurricane. 18)

- At the time the image was captured, Barry had maximum sustained winds of 65 mph (105 km/h). When the storm reaches maximum sustained winds of 74 mph (119 km/h), it will be upgraded to hurricane status. The National Hurricane Center notes that the slow movement of the storm will result in long periods of heavy rain, dangerous storm surge and flooding in parts of the central Gulf Coast into the Lower Mississippi Valley.

- 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 down to Earth's surface. 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. Launched into Earth orbit in 2002, the AIRS and AMSU instruments fly onboard NASA's Aqua spacecraft and are managed by NASA's Jet Propulsion Laboratory in Pasadena, California, under contract to NASA.

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Figure 29: NASA's AIRS instrument imaged Tropical Storm Barry on the afternoon of July 12, 2019, a day before the storm is expected to make landfall on the Louisiana Coast. The infrared image shows very cold clouds that have been carried high into the atmosphere by deep thunderstorms in purple. These clouds are associated with heavy rainfall. Warmer areas with shallower rain clouds are shown in blue and green. And the orange and red areas represent mostly cloud-free air (image credit: NASA/JPL-Caltech)

• July 10, 2019: An upper-level ridge of high pressure that slid over Alaska in June 2019 unleashed a heat wave of astonishing intensity. With temperatures soaring into the 80s and even 90s (Fahrenheit) in some parts of Alaska, several all-time and daily temperature records fell. 19)

- Anchorage, Kenai, and King Salmon broke all-time records on July 4, 2019. In Anchorage, the record was not just broken; it was obliterated. The city reached 90°F (32°C) on Independence Day; the previous record was 85°F (29°C) on June 14, 1969. Daily temperature records have been kept for Anchorage since 1952.

- This heat has also been unusual for how long it has lingered. Anchorage faced six consecutive days where temperatures exceeded 80 degrees, the longest stretch on record. The city broke daily high-temperature records eight times between June 23 and July 8. The normal daily high for Anchorage in July is 62°F (17°C).

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Figure 30: Record-breaking heat has exacerbated clusters of wildfires burning throughout the state. This map shows air temperatures at 2 meters above the ground on July 8, 2019. The near real-time temperature data come from the GEOS forward processing (GEOS-FP) model, which assimilates observations of air temperature, moisture, pressure, and wind speeds from satellites, aircraft, and ground-based observing systems. The darkest red areas had temperatures approaching 32ºC (90ºF), image credit: NASA Earth Observatory, image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview and GEOS-5 data from the Global Modeling and Assimilation Office at NASA GSFC. Story by Adam Voiland.

- In many parts of Alaska, the heat has been accompanied by thick smoke. Clusters of lightning-triggered wildfires have been burning around Fairbanks since June 21, 2019. A second cluster began burning south of the Koyukuk Wilderness on July 5. Fires spread more quickly in hot weather because the amount of heat needed to warm fuels to the ignition point is lower. Fires generally burn with the most intensity in the afternoon, when temperatures are typically warmest.

- As of July 9, there were 38 large fires burning in Alaska. They had consumed a total of 697,000 acres, about 52 percent of all acreage burned in the United States in 2019, according to the National Interagency Fire Center. The largest Alaskan fire, Hess Creek, was burning through forests of black spruce and mixed hardwoods (birch, aspen, and white spruce) north of Fairbanks. It had charred 172,548 acres (69,827 hectares) as of July 9, making it the largest fire in the United States so far in 2019.

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Figure 31: The MODIS instrument on NASA's Aqua satellite captured an image of thick wildfire smoke swirling over the state on 8 July 2019. Meteorologists in Fairbanks reported visibility had dropped to less than one mile due to smoke, and air quality sensors in the city reported skyrocketing levels of particulates in the air (image credit: NASA Earth Observatory, image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview and GEOS-5 data from the Global Modeling and Assimilation Office at NASA GSFC. Story by Adam Voiland)

• June 18, 2019: For most of the year, the Lena River Delta—a vast wetland fanning out from northeast Siberia into the Arctic Ocean—is either frozen over and barren or thawed out and lush. Only briefly will you see it like this. 20)

Figure 32: After seven months encased in snow and ice, the delta emerges for the short Arctic summer. The transition happens fast. This animation, composed of images from the MODIS on NASA's Aqua satellite, shows the transformation from June 3-10, 2019 (image credit: NASA Earth Observatory image by Joshua Stevens, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview, and Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen with image interpretation by Ingmar Nitze/Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, and Hajo Eicken/University of Alaska Fairbanks)

- At this time of year, relatively warm water flows northward from the Lena River; this warms and awakens the delta. River ice melts, breaks up, and gets flushed out of the Lena's branching river channels. Snow and ice on the surface of the delta also begin to melt.

- In the animation, water flows more freely toward the ice-capped Laptev Sea, but it still faces obstacles. Unable to penetrate the permafrost in the ground, and blocked by ice remaining in the river channels, the meltwater produces a huge but short-lived flood. The flood spreads across the delta and over the adjacent sea ice in the Laptev Sea. Sea ice that is grounded—that is, attached to the seafloor—gets submerged; non-grounded sea ice floats to the surface. As the sea ice near the coast melts completely, dark blue seawater is exposed.

- Green areas are likely the result of organic matter (debris from leaves, branches, and peat) dissolved in the water. Siberian rivers tend to contain a high concentration of colored dissolved organic matter (CDOM). The spring meltwater also carries sediments that are sometimes deposited on the ice and adding color to the water.

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Figure 33: The green color near the delta's edge is especially visible in this image, acquired on 4 June 4 2019, by the Operational Land Imager on Landsat-8. You can also see relatively deep river channels traced by bands of bright ice that has broken from the channel edges and floated up. This ice is slower to melt because it absorbs less heat at its surface compared to flooded ice (image credit: NASA Earth Observatory image by Joshua Stevens, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview, and Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen with image interpretation by Ingmar Nitze/Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, and Hajo Eicken/University of Alaska Fairbanks)

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Figure 34: This detailed image, also acquired June 4 with OLI, shows the delta's western side, where the modern, active part of the delta meets the older, drier parts. Water ponds in depressions in the ground formed from thawed permafrost. At the time of the images, these "themokarst lakes" remained frozen, but the delta will take on a completely different look soon (image credit: NASA Earth Observatory image by Joshua Stevens, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview, and Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen with image interpretation by Ingmar Nitze/Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, and Hajo Eicken/University of Alaska Fairbanks)

• June 4, 2019: On land, green plants form the center of the food web, and nearly all other life radiates out from there—consuming those plants or the creatures who eat the plants. In the ocean, phytoplankton are the equivalent of grasses, trees, and shrubs. Floating near the ocean surface, phytoplankton use chlorophyll to harness sunlight, turning carbon dioxide from the air and dissolved nutrients in the water into sugars and oxygen. Nearly all life in the ocean traces its food supply back to these primary producers. 21)

- Blooms are common in this region, especially in spring, as it is dominated by the Oyashio current. The "parent stream" (oya shio in Japanese) nurtures so much life because it carries cool, lower-salinity water from the Bering Sea and sub-Arctic North Pacific. It bears iron and other nutrients from Arctic waters and from the coasts of Kamchatka and Siberia. More nutrients are stirred up from the depths through upwelling. This combination of ocean conditions provides an incredibly fertile environment for bursts of phytoplankton growth, often led by diatoms.

- Blooms tend to be largest here in the early spring because surface waters have been "resting" all winter. That is, the diminished sunlight and turbulent storms of winter keep phytoplankton productivity at a minimum. This allows the iron- and silica-rich dust and ash from Asian deserts and Kamchatkan volcanoes to accumulate in surface waters. The spring blooms then deplete most of these nutrients. Later blooms can be spurred by upwelling, by the collision and mixing of water masses between the Oyashio and the Kuroshio currents, or by sporadic natural events like dust storms that can seed the ocean.

- The blooms on the Oyashio current in turn support some of the most productive fisheries in the world. The phytoplankton feed abundant populations of copepods, euphausiids, and other zooplankton. Walleye pollock, Pacific cod, chum salmon, and pink salmon feed on the plankton buffet, and other migrants—such as sardines, anchovies, Pacific saury, chub mackerel, and squid—pass through seasonally. Whales and seabirds feast on the bounty, and humans reap a strong commercial harvest here.

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Figure 35: Off the coast of Hokkaido, Japan, there was a lot of primary production going on in late May and early June 2019. On June 2, the MODIS instrument on NASA's Aqua satellite caught glimpses of vast blooms of phytoplankton. Their green and light blue tones traced the edges of swirling water masses, currents, and eddies (image credit: NASA Earth Observatory image by Joshua Stevens, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Caption by Michael Carlowicz)

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Figure 36: On May 26, the MODIS instrument on NASA's Aqua satellite caught glimpses of vast blooms of phytoplankton. Their green and light blue tones traced the edges of swirling water masses, currents, and eddies (image credit: NASA Earth Observatory image by Joshua Stevens, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Caption by Michael Carlowicz)

• April 30, 2019: It is one of the most productive patches of water on the planet. It was also the location for our first-ever Image of the Day. 22)

- In the South Atlantic Ocean, off the coast of Argentina, Uruguay, and Brazil, warm currents from tropical waters flow south and run into cooler currents flowing north from the Southern Ocean. They meet in a place known as the Brazil-Malvinas Confluence. At least seven different water masses of varying temperature, depth, and salinity arrive at this turbulent, three-dimensional intersection, leading to vertical and horizontal mixing. With all of the churning—plus nutrient-rich outflows from rivers (such as Rio de la Plata) and dust blown out from Patagonia—this patch of ocean is a factory for phytoplankton.

- Phytoplankton are plant-like floating organisms that use chlorophyll to harness sunlight and turn it into food. They form the center of the ocean food web, becoming food for everything from microscopic animals (zooplankton) to fish to whales. They are key producers of the oxygen that makes the planet livable, and they are critical to the global carbon cycle, as they absorb carbon dioxide from the atmosphere.

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Figure 37: The MODIS image of NASA's Aqua satellite acquired in this dynamic patch of ocean on 15 February 2019. In this natural-color image, we see very faint traces of green and milky blue amidst the inky blue-black of the deep ocean.

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Figure 38: This MODIS image shows concentrations of chlorophyll–a, the primary pigment used by phytoplankton to capture sunlight. The darkest shades of green shown areas with the greatest chlorophyll concentrations. MODIS can see what is opaque to our eyes because it detects a range of visible light, infrared, and near-infrared wavelengths, and because scientists have spent decades refining their tools for spotting the chlorophyll signal amidst the noise of the ocean and atmosphere (image credit: NASA Earth Observatory, images by Joshua Stevens and Robert Simmon, using MODIS data from NASA's Ocean Color Web, Story by Michael Carlowicz)

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Figure 39: This map shows chlorophyll in the same area in 1999 as observed by the SeaWiFS (Sea-viewing Wide Field-of-view Sensor). Chlorophyll concentrations are shown on a rainbow palette, with yellows and reds representing the highest concentrations. The map was the first item ever published on NASA Earth Observatory (image credit: Image processed by Robert Simmon based on data from the SeaWiFS project and the Goddard DAAC. Text by Jim Acker)

- There are similarities and differences. The water was quite productive then as it is now, and it also shows similar swirls and curves where phytoplankton trace the edges of eddies and currents. The details, however, were a bit coarser. SeaWiFS could spot details (image resolution) at a level of four kilometers per pixel; MODIS observes at 1 kilometer per pixel. The colors of the chlorophyll map are also different due to a change in the way Earth Observatory presents data. Just as ocean science has evolved, the study of data mapping and visual communication has taught us to better represent data in ways that are more understandable, more accessible (including the colorblind), and more detailed and nuanced.

- The improvements in our ocean vision have as much to do with improving how we see—how scientists apply the corrective lens of experience and better data filtering—as they do with the quality of ocean-observing satellites. "The orbiting ocean-color sensors we use today are not really that different from 20 years ago," noted Norman Kuring, a NASA ocean color specialist who has been handling such data for three decades. "I think that we are mainly learning gradually about the ecological geography of the ocean through accumulation of data, the pursuit of diverse research projects, and improved atmospheric correction and bio-optical algorithms."

- As NASA Earth Observatory starts its 20th year publishing science stories and imagery, we plan to explore the way the planet and our view of it has changed. This is the first in a year-long series of looks back and forward at Earth system science.

• April 25, 2019: Just weeks after Cyclone Idai left a path of destruction through Mozambique, Cyclone Kenneth is now battering the country in southeast Africa. It is likely the strongest storm on record to hit Mozambique, with wind speeds equivalent to a Category 4 hurricane at landfall. It is also the first time in recent history that the country has been hit by back-to-back hurricane-strength storms. 23)

- NASA's Atmospheric Infrared Sounder (AIRS) instrument captured this infrared image of Kenneth just as the storm was about to make landfall on April 25. The large purple area indicates very cold clouds carried high into the atmosphere by deep thunderstorms. The orange areas are mostly cloud-free; the clear air is caused by air moving outward from the cold clouds near the storm's center, then downward into the surrounding areas.

- The image was taken at 1:30 p.m. local time, just before the cyclone made landfall in northern Mozambique's Cabo Delgado Province. With maximum sustained winds of 140 mph (225 km/h), Kenneth was the first known hurricane-strength storm to make landfall in the province. Heavy rainfall and life-threatening flooding are expected over the next several days.

- AIRS, in conjunction with the Advanced Microwave Sounding Unit (AMSU), 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 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. Launched into Earth orbit in 2002, the AIRS and AMSU instruments fly onboard NASA's Aqua spacecraft and are managed by NASA's Jet Propulsion Laboratory in Pasadena, California, under contract with NASA. JPL is a division of Caltech.

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Figure 40: This infrared image from NASA's AIRS (Atmospheric Infrared Sounder) shows the temperature of clouds or the surface in and around Tropical Cyclone Kenneth as it was about to make landfall in northern Mozambique on Thursday, 25 April. The large purple area indicates very cold clouds carried high into the atmosphere by deep thunderstorms. These storm clouds are associated with heavy rainfall. The orange areas are mostly cloud-free areas, with the clear air caused by air motion outward from the cold clouds near the storm center then downward into the surrounding areas (image credit: NASA/JPL-Caltech)

• April 9, 2019: Forget the transition period between seasons: in March 2019, Alaska jumped from mid-winter right into late spring, setting monthly temperature records in many cities and towns. Meteorologists have noted that the unusually hot month was part of a long-term warming trend in the state in recent years. 24)

- Note that the map (Figure 41) depicts land surface temperatures (LSTs), not air temperatures. LSTs reflect how hot the surface of the Earth would feel to the touch and can sometimes be significantly hotter or cooler than air temperatures.

- March 2019 began with an unsettled weather pattern that brought warm, wet storms to the state, according to the Alaska Climate Research Center. By mid-month, a high-pressure ridge developed and stayed in place for weeks, producing mostly clear skies and very warm temperatures.

- The average temperature for March 2019 set records at 10 of 19 ground-based weather stations in Alaska. Utqiaġvik (Barrow)—the northernmost town in the United States—saw its hottest March in more than 100 years. The town's average high temperature in March is usually -12.6 degrees Fahrenheit (-24.7° Celsius). But in March 2019, the temperature averaged 5.9° Fahrenheit. Delta Junction, Fairbanks, and many towns broke temperature records. You can see a list here.

- The "warm" month in Utqiaġvik did not mean it was a dry month. In March 2019, the town received more than four times the normal amount of rain and twice the amount of snow.

- Warm air temperatures, stormy weather, and warm sea surface temperatures have taken a toll on sea ice in the Bering Sea west of Alaska, bringing its extent even lower than in 2018. Typically, sea ice here reaches a maximum extent in March or early April. Images published by NOAA, however, show that by April 1, 2019, the sea was already largely free of ice. This melting in the Bering Sea put a large dent in the overall Arctic sea ice extent, which on April 1 hit a record low for the date.

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Figure 41: This map shows land surface temperature anomalies from March 1-31, 2019. Red colors depict areas that were hotter than average for the same month from 2000-2012; blues were colder than average. White pixels were normal, and gray pixels did not have enough data, most likely due to excessive cloud cover. This temperature anomaly map is based on data from the MODIS instrument on NASA's Aqua satellite (image credit: NASA Earth Observatory image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview and data from the Level 1 and Atmospheres Active Distribution System (LAADS) and Land Atmosphere Near real-time Capability for EOS (LANCE). Story by Kathryn Hansen)

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Figure 42: While the north and northwest parts of the state were wetter than usual, other parts were unusually dry. These natural-color images, acquired with MODIS on NASA's Terra satellite, show Anchorage on March 30, 2018 (left), and March 30, 2019 (right). According to reports, March 2019 is only the second time on record that there was no measurable snowfall in Anchorage during the month (image credit: NASA Earth Observatory, image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview and data from the Level 1 and Atmospheres Active Distribution System (LAADS) and Land Atmosphere Near real-time Capability for EOS (LANCE). Story by Kathryn Hansen)

• March 12, 2019: In early March 2019, a rash of bushfires sprouted across the Australian state of Victoria, particularly in the hills east of Melbourne. Government officials noted at least 380 small and large fires burned in the state in the first week of the month, with the vast majority caused by lightning. 25)

- An estimated 70,000 hectares (700 km2, 270 square miles) of land burned, with significant fires raging in Bunyip State Park and around Licola, Dargo, Gippsland, and Yinnar South. News agencies reported that the entire town of Tonimbuk was wiped out by fire. Few fatalities have been reported in the state, as government agencies ordered evacuations.

- The fires came particularly late in the season for Victoria, though they were not surprising. Months of intense summer heat and long-term drought have parched much of the landscape and primed the vegetation for burning.

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Figure 43: MODIS on NASA's Aqua satellite acquired a natural-color image of smoke over Victoria on March 7, 2019. Government agencies reported 18 fires were still burning in the state that day, despite two days of rain and cooler weather (image credit: NASA Earth Observatory image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview, story by Mike Carlowicz)

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Figure 44: These natural-color images were acquired within a span of four hours on March 3, 2019. The first image comes from the MODIS instrument on NASA's Terra satellite; the second from the Visible Infrared Imaging Radiometer Suite (VIIRS) on Suomi NPP; and the third from Aqua MODIS. The trio appears to show the formation of bright, tall pyrocumulus clouds. Ground-based photos (here and here) posted by the Australian Bureau of Meteorology seem to affirm that classification (image credit: NASA Earth Observatory, images by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview and VIIRS data from the Suomi National Polar-orbiting Partnership, story by Mike Carlowicz)

- These tall, cauliflower-shaped clouds—sometimes called "fire clouds"—appear as opaque white patches hovering over smoke in satellite imagery. Pyrocumulus clouds form when heat from a fire forces air to rise quickly, which leads to cooling at high altitude and condensation of water vapor into clouds. Under certain circumstances, pyrocumuli can produce full-fledged thunderstorms, making them pyrocumulonimbus clouds.

• January 31, 2019: NASA's AIRS (Atmospheric Infrared Sounder) instrument on Aqua captures a polar vortex moving from Central Canada into the U.S. Midwest from January 20 through January 29, 2019. 26)

Figure 45: The AIRS images show air temperatures at 600 millibars, around 4 km high in Earth's troposphere. This polar vortex is responsible for surface air temperatures as low as -40º F (also -40ºC) and wind chill readings as low as the -50s and -60s Fahrenheit (-46 and -51 Celsius), image credit: NASA/JPL

- The polar vortex is responsible for a number of deaths, disruptions to services, and energy outages in the affected areas.

- AIRS, in conjunction with 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 down to Earth's surface. 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. Launched into Earth orbit in 2002, the AIRS and AMSU instruments fly onboard NASA's Aqua spacecraft and are managed by NASA's Jet Propulsion Laboratory in Pasadena, California, under contract to NASA. JPL is a division of the Caltech in Pasadena.

• January 28, 2019: A new NASA study shows that warming of the tropical oceans (30°N to 30°S) due to climate change could lead to a substantial increase in the frequency of extreme rain storms by the end of the century. 27) 28)

- The study team, led by Hartmut Aumann of NASA's Jet Propulsion Laboratory in Pasadena, California, combed through 15 years of data acquired by NASA's Atmospheric Infrared Sounder (AIRS) instrument over the tropical oceans to determine the relationship between the average sea surface temperature and the onset of severe storms.

- They found that extreme storms - those producing at least 3 mm of rain per hour over a 25 km area - formed when the sea surface temperature was higher than about 82º Fahrenheit (28º Celsius). They also found that, based on the data, 21 percent more storms form for every 1.8º Fahrenheit (1º Celsius) that ocean surface temperatures rise.

- "It is somewhat common sense that severe storms will increase in a warmer environment. Thunderstorms typically occur in the warmest season of the year," Aumann explained. "But our data provide the first quantitative estimate of how much they are likely to increase, at least for the tropical oceans."

- Currently accepted climate models project that with a steady increase of carbon dioxide in the atmosphere (1 percent/year), tropical ocean surface temperatures may rise by as much as 4.8º Fahrenheit (2.7º Celsius) by the end of the century. The study team concludes that if this were to happen, we could expect the frequency of extreme storms to increase by as much as 60 percent by that time.

- Although climate models aren't perfect, results like these can serve as a guideline for those looking to prepare for the potential effects a changing climate may have.

- "Our results quantify and give a more visual meaning to the consequences of the predicted warming of the oceans," Aumann said. "More storms mean more flooding, more structure damage, more crop damage and so on, unless mitigating measures are implemented."

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Figure 46: An "anvil" storm cloud in the Midwestern U.S. (image credit: UCAR)

• December 27, 2018: The ocean is more than just a hue of blue; it runs a gamut of greens to grays and everything in between. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite acquired this image showing swirls of color in the Arabian Sea on November 23, 2018. 29)

- The image of Figure 47 appears like a watercolor painting—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 MODIS data to make the biomass more visible.

- The range of ocean colors represents various types of activity occurring in the waters. For instance, different kinds of sediment—from a variety of soils, rock types, and organic debris—can flow into the ocean and color the water many shades near the shore. Scientists use satellite imagery to monitor sediment outflow and other debris such as dissolved organic material, which can affect water quality.

- Water color can also be affected by the presence of phytoplankton, plant-like organisms that serve as the center of the aquatic food web. Phytoplankton abundance depends on the availability of carbon dioxide, sunlight, and nutrients, but also other factors including water temperature, salinity, depth, wind, and abundance of animals grazing on them. When conditions are right, phytoplankton populations can grow explosively, a phenomenon known as a bloom.

- Phytoplankton blooms—drawn into thin swirling ribbons by turbulent eddies—commonly occur in the Arabian Sea. In the northern Arabian Sea, phytoplankton blooms are strongly influenced by monsoon winds. Large blooms tend to occur in the summer when strong southwesterly winds blow from the ocean towards land, mixing the water. Blooms also happen in the winter when northeast winds blow offshore.

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Figure 47: A colorful image of the Arabian Sea shows the various types of activities occurring in the waters, acquired with MODIS on Aqua on 23 November 2018 (image credit: NASA Earth Observatory, ocean imagery by Norman Kuring, NASA's Ocean Color web. Story by Kasha Patel)

• November 29, 2018: While November typically brings wet weather to Iraq, November 2018 brought even more frequent and intense rain storms than usual. On November 22-23, an especially potent storm dropped torrential rains across northern and central Iraq. 30)

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Figure 48: False-color image of Iraq acquired on 28 October 2018 with MODIS on NASA's aqua satellite (image credit: NASA Earth Observatory, image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Story by Adam Voiland)

- The resulting flash floods have taken several lives, injured hundreds, and displaced tens of thousands of people, according to humanitarian organizations. Hundreds of homes have been destroyed, particularly in towns north of Baghdad, according to news reports.

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Figure 49: November flash floods displaced tens of thousands of people. This false-color image of Iraq was acquired on 27 November 2018 with MODIS on Aqua showing water pooling in the floodplains of central and southern Iraq (image credit: NASA Earth Observatory, image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Story by Adam Voiland)

- The images were both composed in false color, using a combination of infrared and visible light. Flood water appears dark blue; saturated soil is light blue; vegetation is bright green; and bare ground is brown. This band combination makes it easier to see flood water.

• October 31, 2018: This could be a scene out of a spooky movie. But reality is just as morbid for this coffin-shaped iceberg. After 18 years at sea, B-15T has entered a region where Antarctic icebergs go to die. 31)

• November 18, 2018: Great phytoplankton blooms tend to occur at intersections: between land and sea, between different ocean currents, and between seasons. All three may have been at work near South Africa in the first half of November 2018 (Figure 50). 32)

- Phytoplankton are tiny, floating, plant-like cells that turn sunlight into food. They are responsible for nearly half of Earth's primary production—that is, they transform carbon dioxide, sunlight, and nutrients into organic matter. They are the center of the ocean food web, the primary nourishment that fuels life in the sea. The amount and location of phytoplankton affects the abundance and diversity of everything from finfish to shellfish and zooplankton to whales.

- Like land-based plants, phytoplankton require sunlight, water, and nutrients to grow. As the Southern Hemisphere progresses through spring into summer, sunlight is becoming more abundant. Spring and autumn also tend to be times of turbulent winds and changeable weather in both hemispheres, so it is possible the South African bloom was provoked by seasonal winds that stirred up nutrients from coastal waters or through upwelling from the seafloor.

- The waters off of southern Africa are also notoriously turbulent and well-mixed, as two great ocean currents meet in the area. Warm water arrives from the Indian Ocean on the fast-moving Agulhas Current , which flows along the east coast of Africa. The cooler, slower Benguela Current flows north along Africa's southwestern coast. Converging off of South Africa, the currents often generate eddies, rogue waves, and other stirring motions that mix the layers of the ocean and bring nutrients up to the surface.

- Finally, there could be one other stimulus for the current bloom, though the idea is mostly speculation. In the past few weeks, wildfires have burned along the Garden Route near the South African coast, and the smoke was blown seaward on many occasions. Smoky winds can carry ash, dust, metals, and other aerosols and pollutants out over the ocean, where they call fall onto the sea surface.

- Researchers know from other studies that airborne dust and volcanic ash can provide nutrients to provoke phytoplankton blooms, but it is not clear whether airborne particles from a fire could do the same. In 2017, researchers made an impromptu attempt to investigate the impact of California wildfires on the Pacific Ocean.

- In November 2018 near South Africa, there is still too little information to blame the fires, and the more conventional explanations are probably the right ones. "We cannot say much about this case without additional information, such as in situ observations," said Santiago Gassó, a scientist from NASA's Goddard Space Flight Center who has studied the ocean impacts of dust and ash. "In this case, while the causality possibility [fire] is tempting to say, there are so many other more probable reasons."

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Figure 50: The MODIS instrument on NASA's Aqua satellite acquired this natural-color image on 14 November 2018. It shows a bloom of phytoplankton off the south coast of South Africa. The bloom first became visible on 9 November and was still underway on 16 November (image credit: NASA Earth Observatory, image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview, story by Michael Carlowicz)

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Figure 51: On September 23, 2018, when an astronaut on the International Space Station shot this photograph, iceberg B-15T had already left the Southern Ocean. It was spotted in the South Atlantic between South Georgia and the South Sandwich Islands(image credit: NASA Earth Observatory. This astronaut photograph ISS056-E-195042 was acquired with a Nikon D5 digital camera using a 800 mm lens and is provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center. The image was taken by a member of the Expedition 56 crew. Story by Kathryn Hansen)

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Figure 52: This image shows a wide view, acquired the same day by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite, acquired on 23 September 2018. Icebergs like this are known to melt rapidly as they make their way north into warmer waters (image credit: NASA Earth Observatory)

- B-15T's journey to this iceberg graveyard has been a long one. Its parent berg (B-15) first broke away from the Ross Ice Shelf in March 2000. It fractured over time into smaller bergs, many of which continued riding the Antarctic Coastal Current (counter-clockwise) around Antarctica.

- By late 2017, the Weddell Sea gyre had redirected B-15T from its near circumnavigation and sent the berg drifting north.

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Figure 53: By late 2017, the Weddell Sea gyre had redirected B-15T from its near circumnavigation and sent the berg drifting north. This third image was acquired in October 2017 by MODIS on NASA's Aqua satellite. It shows the iceberg when it was near Elephant Island, an icy bit of rock located a few hundred kilometers north-northeast from the tip of the Antarctic Peninsula (image credit: NASA Earth Observatory)

- The Antarctic Circumpolar Current, which funnels through the Drake Passage, then steered the iceberg toward the east and its current location. Water at this latitude—about 54 degrees South—is generally warmer than the Southern Ocean and deadly for icebergs. NASA/UMBC glaciologist Chris Shuman noted that Southern Hemisphere winter was just ending when the astronaut spotted the berg, so the return of abundant sunlight could further warm the water around it. The lack of sea ice in the vicinity of B-15T implies that the water was above the freezing point.

- The spooky shape of B-15T was acquired long before it moved into this iceberg graveyard. For more than a decade, B-15 had numerous collisions—smashing back into the Ross Ice Shelf where it originated, hitting bedrock along the coast, and bumping into other tabular icebergs. Such collisions can be strong enough to abruptly fracture the crystalline ice and produce linear edges—similar to the rectangular iceberg that debuted this month near the Larsen C ice shelf and iceberg A-68. That iceberg is visible in the photograph of Figure 54, acquired on 16 October 2018 during an Operation IceBridge science flight.

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Figure 54: Photo of the B-15T iceberg acquired on 16 October during an Operation Icebridge flight (image credit: NASA Earth Observatory)

- "This fracturing is akin to ‘cleaving' a mineral crystal with a sharp tap of hammer," Shuman said. Of course, the edges are not always so linear. Other bergs have edges that are curved. Some become jagged when the pull of gravity or the cutting action of waves causes ice to irregularly splinter.

- "The coffin shape is an accident of time and space, given the approximately 18.5-year voyage of B-15T," Shuman said. "We can only guess at the forces that have acted on this remnant of B-15 along the long way around Antarctica."

• October 22, 2018: There are fires burning somewhere on the planet every day—nearly one million per year—and satellites help detect them even when no one is talking about them. 33)

Figure 55: MODIS on NASA's Aqua and Terra satellites acquired this series of images between September 15 and October 18, 2018. The fires burned along the border between Botswana and Zimbabwe, in and around Kasane Forest Reserve, Maikaelelo Forest Reserve, and Kazuma Pan National Park. The images were composed from a combination of visible and shortwave infrared light (MODIS bands 7-2-1). The burn scar appears in shades of orange and dark brown; vegetation is green; bare ground is light brown; and water is dark blue (image credit: NASA Earth Observatory, image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Story by Michael Carlowicz)

- "Most, if not all, fires in Africa are man-made in one of its various forms: prescribed, agricultural, accidental, or arson," said climate and fire researcher Charles Ichoku of Howard University. "It is still the fire season in that part of southern Africa, but the behavior of the fires seems curious." The veldt (grassland) fire season in this part of Botswana typically runs from May to November.

- The exact causes of the fires are not clear, and some of the straight fire lines make it appear that these were managed burns. But those distinct lines more likely indicate fire breaks. Anja Hoffmann, a researcher with the Global Observation of Forest and Land Cover Dynamics project, noted that Botswana is covered with a network of fire breaks stretching 10,000 km and with an average width of 20 to 30 meters.

- "The fire started near the tarred road not far from Lesoma on September 15 and extended to the west. It was not a prescribed burn," wrote Jomo Mafoko, a fire manager in Botswana's Department of Forestry and Range Resources. "Even though the fire was difficult to control due to extreme conditions, it was finally put out. Another fire started [to the south], and rains helped to control it. There was a shortage of resources, and the terrain was not easy to maneuver."

- In the 21st Century, satellites have become important for monitoring fires on a local, regional, and global scale. They play a role in helping firefighting agencies control some blazes and in managing the protection of life and resources. On longer time scales, satellite detections help scientists better understand the way fires evolve and spread, what they emit into the atmosphere, and how they respond to changing climate conditions.

- With 19 years of MODIS fire detections in the NASA archives, researchers are building databases and models to better understand fire behavior on regional and global scales. One such effort is the Global Fire Atlas, a web-based dataset that estimates the size, duration, spread rate, and direction of every large fire detected in the MODIS burned area data.

- "This region of northern Botswana burns almost every year," added Doug Morton, a forest and fire expert from NASA's Goddard Space Flight Center who helped develop the fire atlas. "The image sequence shows how roads and other fragmentation of the landscape alter the size and shape of fires—a great illustration of how fire in natural ecosystems responds to human modifications."

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Figure 56: Extend of fires on 18 October 2018 as observed by MODIS (image credit: NASA Earth Observatory, image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Story by Michael Carlowicz)

• October 10, 2018: In September, North Carolina took a direct hit from a hurricane. Now it is Florida's turn. What began as a tropical disturbance in the Caribbean Sea on October 2, 2018, went on to graze the Yucatan Peninsula and then strengthen into Hurricane Michael. The storm continued on its way through the Caribbean Sea and the Gulf of Mexico. 34)

- National Hurricane Center forecasters expect the storm to make landfall in the Florida Panhandle or Big Bend region around midday on 10 October. This area has faced relatively few hurricanes in the past, at least for the U.S. state that sees more landfalling hurricanes than any other.

- "Only eight major hurricanes on record have passed within or near the projected landfall of Michael, and only three of those (Eloise 1975, Opal 1995, and Dennis 2005) were in the past 100 years," noted Marangelly Fuentes, a NASA atmospheric scientist who has been tracking the storm with models maintained by NASA's Global Modeling and Assimilation Office (GMAO). "Michael's projected intensity at landfall is currently category 3, which is worrisome because many people living in the Panhandle have little or no experience with storms this intense."

- As Michael approaches land, two key factors will help govern the intensity of the storm: ocean temperatures and wind shear, the difference in wind speeds at upper and lower parts of a storm. Warm ocean water and low wind shear are required to sustain or intensify a hurricane's strength.

- Michael managed to strengthen despite facing significant westerly shear in the Caribbean Sea on October 9, something the National Hurricane Center called "most unusual." It then passed into an area of low shear and warm ocean water on October 10, where it continued to intensify.

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Figure 57: This map shows SSTs (Sea Surface Temperatures) on October 8-9, 2018. Meteorologists generally agree that SSTs should be above 27.8ºC to sustain and intensify hurricanes (although there are some exceptions). The data for the map were compiled by Coral Reef Watch, which blends observations from the Suomi NPP, MTSAT, Meteosat, and GOES satellites and computer models. Information about the storm track and winds come from the National Hurricane Center (image credit: NASA Earth Observatory, image by Joshua Stevens and Lauren Dauphin using SST data from Coral Reef Watch, story by Adam Voiland)

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Figure 58: The U.S. state that receives more direct hits from hurricanes than any other prepared for yet another one. Forecasters do expect the storm to bring life-threatening winds and storm surge. On 7 October, the governor of Florida declared a state of emergency and urged people in the path of the storm to evacuate. MODIS on Aqua acquired this natural-color image of Hurricane Michael on the afternoon of 8 October 2018 (image credit: NASA Earth Observatory, image by Joshua Stevens and Lauren Dauphin using MODIS data of NASA EOSDIS/LANCE and GIBS/Worldview , story by Adam Voiland)

• October 8, 2018: A little more than 500 miles (800 km) off of West Antarctica, a series of clouds in thin, parallel lines stretched over the open water of the Amundsen Sea. The long parallel bands of cumulus clouds—called cloud streets— are ultimately 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. 35)

- In this case, cool air likely was blowing out from Antarctica and the sea ice cover. As it reached warmer, open water, the winds would have picked up heat and moisture to make the thermals and clouds.

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Figure 59: Cold air blows over warmer water to produce thin, parallel lines of clouds. MODIS on Aqua captured the scene on 12 September 2018 (image credit: NASA Earth Observatory, image by Lauren Dauphin, using MODIS data from LANCE/EOSDIS Rapid Response, text by Kasha Patel)

• September 25, 2018: Activity at the Indonesian volcano Anak Krakatau is not unusual; eruptions have occurred sporadically over the past few decades. And before that, it was the site of the infamous, deadly eruption of 1883. It is somewhat unusual, however, for satellites to get cloud-free views, as they did in September 2018. 36)

- Local sources reported that this eruption has been ongoing since 19 June 2018. Ash plumes have been observed rising to altitudes up to 1.8 km. As of September 24, the eruption had not yet affected air travel in southeast Asia, according to news reports. The local alert status remained at "caution," which is the second-highest level.

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Figure 60: MODIS on NASA's Aqua satellite acquired the wide view of Krakatau on 24 September 2018. Volcanic ash and steam are streaming southwest over the waters of the Sunda Strait (image credit: NASA Earth Observatory using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview, image by Joshua Stevens, story by Kathryn Hansen)

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Figure 61: The MSI (MultiSpectral Imager) on ESA's Sentinel-2satellite acquired this detailed image of Krakatau on 22 September 2018.Ash from the Indonesian volcano streamed over the Sunda Strait (image credit: NASA Earth Observatory using modified Copernicus Sentinel data (2018) processed by the European Space Agency,: image by Joshua Stevens, story by Kathryn Hansen)

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Figure 62: The plume was also visible from the International Space Station. European Space Agency astronaut Alexander Gerst snapped this photograph of the plume on September 24, 2018 (image credit: ISS photograph by Alex Gerst, European Space Agency/NASA, story by Kathryn Hansen)

• September 24, 2018: Throughout most of the year, the waters of Foxe Basin are choked with sea ice. By the end of summer, however, open water typically dominates this part of the Canadian Arctic. That was the case when these images were acquired in September 2018, as small patches of ice lingered in the northern reaches of Hudson Bay around Prince Charles Island and Baffin Island. 37)

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Figure 63: MODIS on NASA's Aqua satellite acquired this wide view on 3 September 2018. Notice in the wide view that the clouds appear whiter than the ice. (image credit: NASA Earth Observatory, image by Lauren Dauphin, using MODIS data from LANCE/EOSDIS Rapid Response, story by Kathryn Hansen)

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Figure 64: OLI on Landsat-8 acquired the detailed view on September 2, 2018. The sea ice that has been tinged brown is common in this part of the Canadian Arctic (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey, story by Kathryn Hansen)

- There are a number of reasons why ice can take on a brown tinge. Particles from natural and human sources—such as aerosols from industrial plants and ship emissions, or mineral dust from land—can blow in. Smoke particles from fires—such as those burning in Siberia in early July—also stream over the sea ice in the Arctic Ocean. If these particles settle onto the ice, they can darken the surface and increase melting.

- Airborne sources, however, are probably not the reason for the brown ice in these images. The Foxe Basin is known for sea ice that gets stained brown by sediment from the surrounding land or from the shallow seafloor. Check out this image from 2012 when seasonal melting started earlier than usual, and pockmarked brown ice prevailed in July. Another image from August 2016 shows a similar view. Greg McCullough of the University of Manitoba points out that some of the color could also be caused by algae, which can grow under the ice and wash up onto the surface during a storm.

- Tidal currents and winds can move the sea ice around and organize it into various patterns and tendrils. According to Jennifer Lukovich, also of the University of Manitoba, the sea ice in this image shows a signature of cyclonic sea ice circulation southwest of Prince Charles Island.

• September 12, 2018: All eyes were on Hurricane Florence Wednesday as the Category 3 storm barreled toward the U.S. East Coast. NASA's Atmospheric Infrared Sounder (AIRS) instrument was watching, too, and captured new imagery of the storm's approach. 38)

- AIRS, in conjunction with the Advanced Microwave Sounding Unit (AMSU), senses emitted infrared and microwave radiation from Earth to provide a three-dimensional look at weather and climate. It acquired infrared and visible light images at 1:30 p.m. EDT Wednesday. In the infrared image, a symmetrical ring of deep, cold rain clouds is shown in purple. Warmer areas, including a well-defined eye, are shown in blue. Shallower rain clouds are shown in green, while the red areas represent mostly cloud-free air moving away from the storm. The visible light image shows Florence much as our eyes would see it. It showcases the storm's thick cloud shield with clouds that extend far from the eye of the storm.

- Hurricane Florence underwent rapid intensification from a Category 2 storm to a Category 4 storm earlier this week. Although it was downgraded to Category 3 on Wednesday, the storm remains large and powerful with the potential for devastating winds, rain and storm surges. States of emergency have already been declared in several states along the coast.

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Figure 65: This image shows Hurricane Florence in infrared light, and was taken at 1:35 p.m. local time on Wednesday, September 12, 2018 by AIRS on board NASA's Aqua satellite. Florence underwent rapid intensification from Category 2 to Category 4 yesterday and was a Category 3 storm as of Wednesday evening (image credit: NASA/JPL-Caltech)

• September 9, 2018: Brazil's cerrado has long been labeled the world's most biologically rich savannah. Nestled between the Amazon and the coastal Atlantic Forest, the region is home to almost 1,000 species of birds and nearly 300 mammals, including the endangered jaguar, maned wolf, and cerrado fox. But over the past few decades, the tropical grassland savannah has been plowed under to make room for a lucrative, protein-packed cash crop: soybeans. 39)

- The top export of Brazil, soybeans represent 90 percent of all agriculture in the cerrado, which covers around one-fifth of the country (larger than California and Alaska combined). The majority of the production comes from the Matopiba region, an acronym for the confluence of the four Brazilian states of Maranhao, Tocantins, Piaui, and Bahia. This image of Matopiba was acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite on September 1, 2018. Planted along the border of western Bahia, soybeans (which derive 35 to 38 percent of their calories from proteins) allow farmers to pack in more protein per hectare than any other large-scale crop.

- From 2010 to 2015, soy exports from Matopiba doubled from 3.5 to 7.1 million tons. Reports predict that the country will become the largest producer of soybeans in the world by 2025, surpassing the United States.

- But the soybean farm expansion is threatening the biological diversity of the cerrado. From 2000 to 2014, agricultural land use in the cerrado increased by 87 percent, with the majority of plots wiping out native vegetation. In April 2017, Brazil's top two scientific associations wrote to the government asking for public policies on sustainable use of this land. Reports state that only 8 percent of the cerrado is currently off-limits to development or agriculture. Organizations are working to create sustainable practices of food production with environmental protection.

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Figure 66: In Brazil, vast wild areas have been converted into farms, producing a major protein-packed cash crop but also endangering wildlife. MODIS on Aqua acquired this image of Matopiba on 1 September 2018 (image credit: NASA Earth Observatory, image by Lauren Dauphin using MODIS data from LANCE/EOSDIS Rapid Response. Story by Kasha Patel)

• September 3, 2018: Summer is the time for ship tracks—especially off the west coast of North America. In August 2018, long, narrow clouds stood out against the backdrop of marine clouds blanketing much of the North Pacific Ocean. Known as ship tracks, the distinctive clouds form when water vapor condenses around the tiny particles emitted by ships in their exhaust. Ship tracks typically form in areas where thin, low-lying stratus and cumulus clouds are present. 40)

- Some 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 especially bright and thick.

- MODIS on Aqua captured this natural-color image of several ship tracks extending northward on August 26, 2018. The clouds were located about 1,000 km west of the California-Oregon border. Similar environmental conditions also triggered the formation of ship tracks in this part of the Pacific on August 27 and 28.

- An analysis of one year of satellite observations from the Advanced Along Track Scanning Radiometer (AATSR) on the European Space Agency's Envisat indicates that very low clouds are most often present off the west coasts of North and South America.

- The large number of ships traversing the North Pacific, combined with all of the low clouds, make ship tracks more common here than anywhere else in the world. Roughly two-thirds of the world's ship tracks are found in the Pacific, according to the study. Other ship track hotspots were in the North Atlantic, off the west coast of southern Africa, and off the west coast of South America.

- The research team also detected a clear seasonality in their occurrence: they are most often observed in May, June, and July, and only occasionally present in December, January, and February. Ship traffic is roughly constant throughout the year, so the cycle is mostly due to seasonal changes in the abundance of very low clouds.

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Figure 67: Ship tracks in the North Pacific acquired with MODIS on 26 August 2018 (image credit: NASA Earth Observatory image by Lauren Dauphin, using MODIS data from LANCE/EOSDIS Rapid Response. Story by Adam Voiland, with information from Bastiaan van Diedenhoven of NASA GISS)

• 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. 41)

Figure 68: 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. 42)

Figure 69: 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. 43)

- 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.

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Figure 70: 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. 44)

- 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.

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Figure 71: 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. 45)

Figure 72: 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. 46)

- 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."

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Figure 73: 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)

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Figure 74: 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.

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Figure 75: 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. 47)

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Figure 76: 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. 48)

- A winter phytoplankton bloom is visible in this image of Figure 77, 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."

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Figure 77: 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.

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Figure 78: 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. 49)

- 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 79). 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 80 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.

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Figure 79: 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)

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Figure 80: 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. 50)

- 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 81). The MODIS instrument on the Terra satellite acquired the image of Figure 82, 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.

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Figure 81: 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)

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Figure 82: 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. 51)

- 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.

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Figure 83: 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 84 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.

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Figure 84: Snow water equivalent (image credit: NASA Earth Observatory, Ref. 51)

- 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 85 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."

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Figure 85: 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. 51)

• 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. 52)

- The temperature anomaly map of Figure 87 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.

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Figure 86: 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.

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Figure 87: 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 88 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.

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Figure 88: 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. 53)

- 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 89). 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.

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Figure 89: 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. 54)

- 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 90 (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.

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Figure 90: 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)