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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: An introduction to Aqua (video credit: NASA)

 


 

Mission status:

• 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. 5)

- 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 5: 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 6: 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. 6)

- 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 7: 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 8: 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 9: 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. 7)

- 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 10: 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. 8)

- Note that the map (Figure 11) 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 11: 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 12: 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. 9)

- 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 13: 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 14: 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. 10)

Figure 15: 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. 11) 12)

- 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 16: 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. 13)

- The image of Figure 17 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 17: 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. 14)

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Figure 18: 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 19: 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. 15)

• 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 20). 16)

- 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 20: 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 21: 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 22: 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 23: 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 24, acquired on 16 October 2018 during an Operation IceBridge science flight.

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Figure 24: 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. 17)

Figure 25: 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 26: 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. 18)

- 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 27: 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 28: 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. 19)

- 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 29: 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. 20)

- 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 30: 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 31: 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 32: 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. 21)

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Figure 33: 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 34: 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. 22)

- 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 35: 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. 23)

- 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 36: 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. 24)

- 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 37: 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. 25)

Figure 38: 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. 26)

Figure 39: 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. 27)

- 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 40: 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. 28)

- 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 41: 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. 29)

Figure 42: 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. 30)

- 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 43: 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 44: 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 45: 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. 31)

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Figure 46: 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. 32)

- A winter phytoplankton bloom is visible in this image of Figure 47, 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 47: 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 48: 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. 33)

- 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 49). 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 50 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 49: 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 50: 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. 34)

- 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 51). The MODIS instrument on the Terra satellite acquired the image of Figure 52, 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 51: 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 52: 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. 35)

- 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 53: 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 54 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 54: Snow water equivalent (image credit: NASA Earth Observatory, Ref. 35)

- 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 55 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 55: 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. 35)

• 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. 36)

- The temperature anomaly map of Figure 57 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 56: 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 57: 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 58 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 58: 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. 37)

- 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 59). 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 59: 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. 38)

- 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 60 (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 60: The left map is a MODIS natural color image of the Ventura fire, the corresponding right map shows the concentration of carbon monoxide in the area acquired with AIRS. Aqua acquired these data on 11 Dec. 2017 (image credit: NASA Earth Observatory, images by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response and AIRS data from the Goddard Earth Sciences Data and Information Services Center (GES DISC), story by Kathryn Hansen)

• December 8, 2017: About 250 km from the Antarctic mainland, the ice-capped tops of the Balleny Islands protrude from the Southern Ocean. Located near the intersection of opposing wind and current systems, the archipelago's three main islands can be battered by weather from all sides. 39)

- But when satellites acquired these images on November 26, 2017, the winds were probably not that turbulent, allowing the formation of organized wave patterns in the clouds and at the ocean's surface. Jan Lieser, a marine glaciologist from Australia's Antarctic Climate and Ecosystems Cooperative Research Center, noticed the curious patterns while browsing satellite images.

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Figure 61: This image shows a wave pattern in the clouds, as observed by MODIS on NASA's Aqua satellite. The image, acquired on 26 Nov. 2017, is false-color, using MODIS bands 7-2-1 to help distinguish clouds (white) from sea ice (blue), image credit: NASA Earth Observatory, image by Joshua Stevens, using MODIS data from LANCE/EOS DIS Rapid Response, story by Kathryn Hansen

- Jan Lieser thinks that a laminar, eastward flow of air hit a speed-bump—Sturge Island—which triggered a low frequency wave pattern to form on the island's lee side. The flow's upper layers reached high enough for water vapor to condense and form clouds. The wave ridges are spaced about 15 km apart and persist for about 200 km east of the island.

- "The cloud pattern can be compared to a lonesome ship sailing on an otherwise smooth lake or ocean and creating these well-known wave traces behind it," Lieser said. "Except here it's the medium (air) that is flowing around the obstacle (island) and not the disturbance (ship) travelling though the medium (water surface)."

- The phenomenon is not entirely unusual. Perhaps more notable is that the pattern also shows up on the ocean surface. Sea surface waves are visible in the image of Figure 62, acquired on the same day by the SAR (Synthetic Aperture Radar) on the European Space Agency's Sentinel-1B satellite. SAR can penetrate clouds to map surfaces below.

- The grayscale image represents differences in surface roughness. The roughest surfaces, particularly Sturge Island, appear brightest. Smoother surfaces—such as sea ice and parts of the open water—appear dark. Roughness also shows up in a wave-pattern across areas of open water, and in the cracks and openings between the sea ice floes.

- Jan Lieser thinks that the same wind that rippled in the sky to form clouds behind the island also came down and roughened the water surface. "If there was a dinghy on the open water east of Sturge Island at the time," he said, "I suspect the sailor would have experienced long-period trains or rippled water passing by and interchanging with smooth periods on an otherwise calm and pleasant day."

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Figure 62: Sentinel-1B SAR image of the Sturge Island region, acquired on 26 Nov. 2017, showing the sea surface waves corresponding to the cloud patterns of Figure 61 (image credit: NASA Earth Observatory, image by Joshua Stevens, using modified Copernicus Sentinel data (2017) processed by the European Space Agency)

• November 16, 2017: Though much of eastern North America just endured a wintry cold snap, it was not that long ago that the weather felt summery. In fact, it was just two weeks ago—well into autumn. 40)

- Weather records fell across the northeastern United States and Canada's Quebec and Maritime provinces in October 2017. According to the U.S. NCEI (National Centers for Environmental Information), the month was the warmest on record (since 1895) for all six New England states. Maine, New Hampshire, Massachusetts, Vermont, Rhode Island, and Connecticut all witnessed monthly average temperatures that were 4.2-4.4ºC above the 20th century average.

- Temperatures also were much warmer than average in the Mid-Atlantic and Great Lakes regions, as well as the far Southwest. At least 20 cities—including Burlington, Albany, Portland, and New York City—set new October records. In contrast, six cities in the Rocky Mountains reported October temperatures that were among their top-10 coldest.

- Environment Canada reported that dozens of cities across eastern Canada had their warmest September and October on record, including Ottawa, Montreal, Quebec, Fredericton, and Halifax. The long-term average temperature in Montreal across both months is typically 12.0°C, but this year the city saw a record-breaking average of 15.9°C. Similarly, Ottawa measured a two-month average of 14.5°C, compared to the long-term average of 11.5°C. Toronto fell just short of its warmest September and October on record.

- The nationally averaged U.S. temperature for October 2017 was 13.2°C, which is 0.9°C above the 20th century average. The warm October temperatures in Canada and the U.S. Northeast were attributed to a strong ridge of high pressure that caused a large northward bulge in the jet stream.

- According to NCEI, the span of January through October has been the third warmest and second wettest on record for the lower 48 United States.

- The map of Figure 63 shows land surface temperature anomalies for October 2017 compared to the average conditions for all Octobers between 2002-2016. The measurements represent the temperature of the top 1 millimeter of the land surface during the daytime. LSTs (Land Surface Temperatures) should not be confused with air temperatures; LSTs reflect the heating of forests, grasslands, cities, and bare ground by sunlight, and they can sometimes differ significantly from air temperatures.

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Figure 63: The data come from AIRS (Atmospheric Infrared Sounder) on NASA's Aqua satellite. AIRS is a hyperspectral infrared sensor that observes atmospheric and surface conditions at 2,378 separate wavelengths. This makes it possible for scientists to create three-dimensional temperature profiles that go from the surface to 40 km in altitude (image credit: NASA Earth Observatory, image by Joshua Stevens, using AIRS data from the Goddard Earth Sciences Data and Information Services Center (GES DISC). Story by Mike Carlowicz. Special thanks to climatologist David Phillips of Environment Canada)

• November 15, 2017: Scientists first reported major dust storms in southern Alaska in 1911, but only during the past decade have they begun to find that high-latitude dust storms play a role in fueling phytoplankton blooms. In 2011, Santiago Gassó of NASA's Goddard Space Flight Center, John Crusius of the U.S. Geological Survey, and other scientists published the first study to describe how dust storms play a role in supplying nutrients, particularly iron, to the Gulf of Alaska. Since then, each successive dust storm has offered these scientists new opportunities to tease out details of the complicated relationship between dust and Gulf of Alaska phytoplankton. 41)

- On November 11, 2017, MODIS (Moderate Resolution Imaging Spectroradiometer ) on NASA's Aqua satellite captured this image of the coast along the Gulf of Alaska (Figure 64). Thick plumes of dust—mainly fine-grained loess formed when glacial ice pulverizes rock—blew south from river valleys. Dust storms in southern Alaska generally occur in late fall, when river levels are relatively low, snow has not yet fallen, and layers of loess-rich mud are exposed to the wind.

- Since light is also crucial to phytoplankton growth, Gassó and his colleagues propose that the influence of dust falling in the ocean may be delayed until the following spring. To get a better understanding of the relationship, the scientists are trying to determine how much iron is supplied by dust storms, as compared to the upwelling of nutrient-rich water from the depths or the mixing of iron-rich sediments (runoff from rivers) by surface eddies and gyres. However, the latter phenomena tend to be coastal, whereas wind-blown dust can cross hundreds of miles of open ocean to areas where iron is normally depleted.

- "It is convenient that we have a phenomenon happening right in our backyard that lends itself to studying the factors that controls marine phytoplankton growth," said Gassó, noting that much of the research on this topic has been done in the Southern Ocean around Antarctica.

- Studying modern dust storms can also make scientists better at interpreting ice cores, which record past environmental conditions and changes in climate. Many ice samples show evidence of both increased dust deposition and decreased concentrations of carbon dioxide in the air during glacial periods (ice ages). It is not yet clear why increased dust and low levels of atmospheric carbon dioxide would go hand-in-hand, but some scientists think that dust-triggered phytoplankton blooms, which can absorb large amounts of carbon dioxide, may have played a key role.

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Figure 64: The MODIS instrument on the Aqua satellite captured the dust storm in the Gulf of Alaska on 11 Nov. 2017 (image credit: NASA Earth Observatory, image by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response. Story by Adam Voiland)

• November 1, 2017: The waters off of southwestern Africa are some of the most biologically productive and chemically interesting in the world. They also provide a compelling backdrop for exploring how satellite sensors and creative data processing can reveal important details of the ocean. 42)

- Flowing up the coast of South Africa, Namibia, and Angola, the Benguela Current is the eastern boundary of a large gyre in the South Atlantic Ocean. The current mixes water from the Atlantic and Indian Oceans as they meet off the capes of South Africa. Thanks to this current and to prevailing winds out of the southeast, this portion of the Atlantic is an area of ocean upwelling.

- Warm surface waters are driven away from the coast, allowing cooler, nutrient-rich waters to rise up from the seafloor. Plumes of hydrogen sulfide sporadically burst from the oxygen-starved depths, a result of bacteria consuming organic material near the bottom and the natural pumping action of upwelling. Air temperatures along the desert coast of southwest Africa are also moderated by the cooler water.

- This dynamic wind and water action causes the ocean to teem with life, from plankton to fish to whales. It all starts with phytoplankton, floating plant-like microorganisms that provide the core source of food for marine ecosystems. The phytoplankton find a near-perfect blend of nutrients, water temperatures, and sunlight to fuel massive blooms. They often show themselves to satellites as an abundance of chlorophyll, the green pigment that helps plants convert sunlight to energy.

- The data for all of the images on this page were acquired by the MODIS instruments on NASA's Aqua satellite on September 2, 2017. The sensor observes Earth in 36 different spectral bands; photo-like imagery is most often built from data in the first seven bands.

- The image of Figure 65 shows the Benguela Current region in natural-color, combining red, green, and blue light (MODIS bands 1-4-3) much as you might see with the human eye. Near the coast, you can see a dark shade of green indicating chlorophyll-rich water. Farther from the coast, the patches of green are harder to detect due to thin clouds and sunglint—the reflection of sunlight back at the MODIS imager (radiometer).

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Figure 65: MODIS image of the south-west coast of Africa and the South Atlantic Ocean acquired on 2 September 2017 (image credit: NASA Earth Observatory, images by Jesse Allen, using data from the Level 1 and LAADS (Atmospheres Active Distribution System), and ocean imagery by Norman Kuring, NASA's Ocean Color web, story by Mike Carlowicz)

- Figure 66 shows concentrations of chlorophyll in the ocean. MODIS instruments have been flying in space since 1999, and other ocean-color detecting instruments have been flying for more than three decades. Over those years, scientists have refined data processing and computer algorithms to better distinguish the light reflected and emitted by chlorophyll from other colors of light detected in the ocean. The result is that it is easier to see the details and hidden abundances of chlorophyll (and therefore, phytoplankton) in the water.

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Figure 66: MODIS image of the south-west coast of Africa and the South Atlantic Ocean acquired on 2 September 2017 (image credit: NASA Earth Observatory, images by Jesse Allen, using data from the Level 1 and LAADS (Atmospheres Active Distribution System), and ocean imagery by Norman Kuring, NASA's Ocean Color web, story by Mike Carlowicz)

- The image of Figure 67 is a blend of art and science. Like a photographer adjusting lighting and using filters, Norman Kuring of NASA's Ocean Biology group works with various software programs and color-filtering techniques to draw out the fine details in the water. The detailed swirls in the chlorophyll-rich water are all quite real; Kuring simply separates and enhances certain shades and tones in the radiometer data to make the biomass more visible.

- "There is some scientific value in this sort of processing in the qualitative sense," Kuring notes. "For example, I have sent these qualitative, feature-rich images to scientists on research cruises to help them plan their cruise tracks. When sampling the open ocean, researchers often want to drop their instruments into frontal regions where the most interesting phenomena occur. Images like these make such regions more apparent by enhancing gradients."

- "But my main goal in making images like these is to pique the viewer's interest and, hopefully, make them more curious about the ocean," Kuring added. "Even folks who have spent their whole lives studying the ocean only know a tiny bit about it. So the more minds that think ‘I wonder why?' the better."

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Figure 67: MODIS image of the south-west coast of Africa and the South Atlantic Ocean acquired on 2 September 2017 (image credit: NASA Earth Observatory, images by Jesse Allen, using data from the Level 1 and LAADS (Atmospheres Active Distribution System), and ocean imagery by Norman Kuring, NASA's Ocean Color web, story by Mike Carlowicz)