Earth Science Studies

GRACE Mission: 15 Years of Watching Water on Earth

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Written by Carol Rasmussen
NASA Earth Science News Team


Artists_concept_of_the_Gravity_Recovery_and_Climate_Experiment_GRACE_from_December_2002.jpg
Artists concept of the Gravity Recovery and Climate Experiment GRACE from December 2002


Fast Facts

  • In 15 years of operations, the GRACE satellite mission has revolutionized our view of how water moves and is stored on Earth.
  • GRACE measures changes in the local pull of gravity as water shifts around Earth due to changing seasons, weather and climate processes.
  • Among other innovations, GRACE gave us the first space-based view of water beneath Earth’s surface, giving insight into where aquifers may be shrinking or dry soils contributing to drought.
  • The GRACE Follow-On mission, launching in early 2018, will extend GRACE’s innovative measurements

 

“Revolutionary” is a word you hear often when people talk about the GRACE mission. Since the twin satellites of the U.S./German Gravity Recovery and Climate Experiment  launched on March 17, 2002, their data have transformed scientists’ view of how water moves and is stored around the planet.

“With GRACE, we effectively created a new field of spaceborne remote sensing: tracking the movement of water via its mass,” said Michael Watkins, the original GRACE project scientist and now director of NASA’s Jet Propulsion Laboratory, Pasadena, California.

Read the rest of this entry »

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NASA Satellite Finds Unreported Source of Toxic Air Pollution

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Human-made sulfur dioxide emissions from a medium-size power plant
New research has detected smaller sulfur dioxide concentrations and sources around the world, including human-made sources such as medium-size power plants and oil-related activities.
Credit: EPA
 
Data from NASA’s Aura spacecraft, illustrated here, were analyzed by scientists to produce improved estimates of sulfur dioxide sources and concentrations worldwide between 2005 and 2014.

Credit: NASA

Using a new satellite-based method, scientists at NASA, Environment and Climate Change Canada, and two universities have located 39 unreported and major human-made sources of toxic sulfur dioxide emissions.

A known health hazard and contributor to acid rain, sulfur dioxide (SO2) is one of six air pollutants regulated by the U.S. Environmental Protection Agency. Current, sulfur dioxide monitoring activities include the use of emission inventories that are derived from ground-based measurements and factors, such as fuel usage. The inventories are used to evaluate regulatory policies for air quality improvements and to anticipate future emission scenarios that may occur with economic and population growth.

But, to develop comprehensive and accurate inventories, industries, government agencies and scientists first must know the location of pollution sources.

“We now have an independent measurement of these emission sources that does not rely on what was known or thought known,” said Chris McLinden, an atmospheric scientist with Environment and Climate Change Canada in Toronto and lead author of the study published this week in Nature Geosciences. 

“When you look at a satellite picture of sulfur dioxide, you end up with it appearing as hotspots – bull’s-eyes, in effect — which makes the estimates of emissions easier.”

The 39 unreported emission sources, found in the analysis of satellite data from 2005 to 2014, are clusters of coal-burning power plants, smelters, oil and gas operations found notably in the Middle East, but also in Mexico and parts of Russia. In addition, reported emissions from known sources in these regions were — in some cases — two to three times lower than satellite-based estimates. 

Altogether, the unreported and underreported sources account for about 12 percent of all human-made emissions of sulfur dioxide – a discrepancy that can have a large impact on regional air quality, said McLinden.

The research team also located 75 natural sources of sulfur dioxide — non-erupting volcanoes slowly leaking the toxic gas throughout the year. While not necessarily unknown, many volcanoes are in remote locations and not monitored, so this satellite-based data set is the first to provide regular annual information on these passive volcanic emissions.

“Quantifying the sulfur dioxide bull’s-eyes is a two-step process that would not have been possible without two innovations in working with the satellite data,” said co-author Nickolay Krotkov, an atmospheric scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. 

First was an improvement in the computer processing that transforms raw satellite observations from the Dutch-Finnish Ozone Monitoring Instrument aboard NASA’s Aura spacecraft into precise estimates of sulfur dioxide concentrations. Krotkov and his team now are able to more accurately detect smaller sulfur dioxide concentrations, including those emitted by human-made sources such as oil-related activities and medium-size power plants. 

Being able to detect smaller concentrations led to the second innovation. McLinden and his colleagues used a new computer program to more precisely detect sulfur dioxide that had been dispersed and diluted by winds. They then used accurate estimates of wind strength and direction derived from a satellite data-driven model to trace the pollutant back to the location of the source, and also to estimate how much sulfur dioxide was emitted from the smoke stack.

“The unique advantage of satellite data is spatial coverage,” said Bryan Duncan, an atmospheric scientist at Goddard. 

“This paper is the perfect demonstration of how new and improved satellite datasets, coupled with new and improved data analysis techniques, allow us to identify even smaller pollutant sources and to quantify these emissions over the globe.”

The University of Maryland, College Park, and Dalhousie University in Halifax, Nova Scotia, contributed to this study.

For more information about, and access to, NASA’s air quality data, visit: http://so2.gsfc.nasa.gov/

NASA uses the vantage point of space to increase our understanding of our home planet, improve lives, and safeguard our future. NASA develops new ways to observe and study Earth’s interconnected natural systems with long-term data records. The agency freely shares this unique knowledge and works with institutions around the world to gain new insights into how our planet is changing. 

For more information about NASA Earth science research, visit: http://www.nasa.gov/earth

NASA Study Solves Two Mysteries About Wobbling Earth

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Earth does not always spin on an axis running through its poles. Instead, it wobbles irregularly over time, drifting toward North America throughout most of the 20th Century (green arrow). That direction has changed drastically due to changes in water mass on Earth. Credit: NASA/JPL-Caltech


Using
satellite data on how water moves around Earth, NASA scientists have solved two mysteries about wobbles in the planet’s rotation — one new and one more than a century old. The research may help improve our knowledge of past and future climate. 

Although a desktop globe always spins smoothly around the axis running through its north and south poles, a real planet wobbles. Earth’s spin axis drifts slowly around the poles; the farthest away it has wobbled since observations began is 37 feet (12 meters). These wobbles don’t affect our daily life, but they must be taken into account to get accurate results from GPS, Earth-observing satellites and observatories on the ground. 

In a paper ‘Climate–Driven Polar Motion: 2003–2015 (PDF)‘ published today in Science Advances, Surendra Adhikari and Erik Ivins of NASA’s Jet Propulsion Laboratory, Pasadena, California, researched how the movement of water around the world contributes to Earth’s rotational wobbles. Earlier studies have pinpointed many connections between processes on Earth’s surface or interior and our planet’s wandering ways. For example, Earth’s mantle is still readjusting to the loss of ice on North America after the last ice age, and the reduced mass beneath that continent pulls the spin axis toward Canada at the rate of a few inches each year. But some motions are still puzzling.


A Sharp Turn To The East

Before about 2000, Earth’s spin axis was drifting toward Canada (green arrow, left globe). JPL scientists calculated the effect of changes in water mass in different regions (center globe) in pulling the direction of drift eastward and speeding the rate (right globe). Credit: NASA/JPL-Caltech

Around the year 2000, Earth’s spin axis took an abrupt turn toward the east and is now drifting almost twice as fast as before, at a rate of almost 7 inches (17 centimeters) a year. “It’s no longer moving toward Hudson Bay, but instead toward the British Isles,” said Adhikari. “That’s a massive swing.” Adhikari and Ivins set out to explain this unexpected change.

Scientists have suggested that the loss of mass from Greenland and Antarctica’s rapidly melting ice sheet could be causing the eastward shift of the spin axis. The JPL scientists assessed this idea using observations from the NASA/German Aerospace Center Gravity Recovery and Climate Experiment (GRACE) satellites, which provide a monthly record of changes in mass around Earth. Those changes are largely caused by movements of water through everyday processes such as accumulating snowpack and groundwater depletion. They calculated how much mass was involved in water cycling between Earth’s land areas and its oceans from 2003 to 2015, and the extent to which the mass losses and gains pulled and pushed on the spin axis.

Adhikari and Ivins’ calculations showed that the changes in Greenland alone do not generate the gigantic amount of energy needed to pull the spin axis as far as it has shifted. In the Southern Hemisphere, ice mass loss from West Antarctica is pulling, and ice mass gain in East Antarctica is pushing, Earth’s spin axis in the same direction that Greenland is pulling it from the north, but the combined effect is still not enough to explain the speedup and new direction. Something east of Greenland has to be exerting an additional pull.

The researchers found the answer in Eurasia. 

“The bulk of the answer is a deficit of water in Eurasia: the Indian subcontinent and the Caspian Sea area,” Adhikari said. 

The finding was a surprise. This region has lost water mass due to depletion of aquifers and drought, but the loss is nowhere near as great as the change in the ice sheets. 

So why did the smaller loss have such a strong effect? The researchers say:

“It’s because the spin axis is very sensitive to changes occurring around 45 degrees latitude, both north and south. “This is well explained in the theory of rotating objects,” Adhikari explained. “That’s why changes in the Indian subcontinent, for example, are so important.””


New Insight on an Old Wobble
In the process of solving this recent mystery, the researchers unexpectedly came up with a promising new solution to a very old

The relationship between continental water mass and the east-west wobble in Earth’s spin axis. Losses of water from Eurasia correspond to eastward swings in the general direction of the spin axis (top), and Eurasian gains push the spin axis westward (bottom). Credit: NASA/JPL-Caltech

problem, as well. One particular wobble in Earth’s rotation has perplexed scientists since observations began in 1899. Every six to 14 years, the spin axis wobbles about 20 to 60 inches (0.5 to 1.5 meters) either east or west of its general direction of drift. “Despite tremendous theoretical and modeling efforts, no plausible mechanism has been put forward that could explain this enigmatic oscillation,” Adhikari said.

Lining up a graph of the east-west wobble during the period when GRACE data were available against a graph of changes in continental water storage for the same period, the JPL scientists spotted a startling similarity between the two. Changes in polar ice appeared to have no relationship to the wobble — only changes in water on land. Dry years in Eurasia, for example, corresponded to eastward swings, while wet years corresponded to westward swings.

When the researchers input the GRACE observations on changes in land water mass from April 2002 to March 2015 into classic physics equations that predict pole positions, they found that the results matched the observed east-west wobble very closely. “This is much more than a simple correlation,” coauthor Ivins said. “We have isolated the cause.”

The discovery raises the possibility that the 115-year record of east-west wobbles in Earth’s spin axis may, in fact, be a remarkably good record of changes in land water storage. “That could tell us something about past climate — whether the intensity of drought or wetness has amplified over time, and in which locations,” said Adhikari. 

“Historical records of polar motion are both globally comprehensive in their sensitivity and extraordinarily accurate,” said Ivins. “Our study shows that this legacy data set can be used to leverage vital information about changes in continental water storage and ice sheets over time.”

GRACE is a joint NASA mission with the German Aerospace Center (DLR) and the German Research Center for Geosciences (GFZ), in partnership with the University of Texas at Austin. For more information on the mission, visit: http://grace.jpl.nasa.gov or http://www.csr.utexas.edu/grace

NASA uses the vantage point of space to increase our understanding of our home planet, improve lives and safeguard our future. NASA develops new ways to observe and study Earth’s interconnected natural systems with long-term data records. The agency freely shares this unique knowledge and works with institutions around the world to gain new insights into how our planet is changing.

For more information about NASA’s Earth science activities, visit: http://www.nasa.gov/earth

New NASA Web Portal Shines Beacon on Rising Seas

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Fort Lauderdale, Florida, is at risk from rising sea levels. Credit: Dave/Flickr Creative Commons/CC BY 2.0

 

Sea level rise is a critical global issue affecting millions across our planet. A new Web portal developed by NASA’s Jet Propulsion Laboratory, Pasadena, California, gives researchers, decision makers and the public alike a resource to stay up to date with the latest developments and scientific findings in this rapidly advancing field of study. 

The portal, “Sea Level Change: Observations from Space,” is online at: https://sealevel.nasa.gov/

The portal’s key features include:
 

  • “Understanding Sea Level,” a summary of decades of scientific research that has shaped our knowledge of sea level rise: its causes, including a warming, expanding ocean and melting ice on land; projections of future sea level rise; and ways in which humanity might adapt, largely drawn from NASA data.
     
  • An interactive data analysis tool, launching in mid-2016, that will allow direct access to NASA datasets on sea level. Users will be able to manipulate these datasets to automatically generate charts, graphs and maps of sea surface height, temperature and other factors. The analysis tool will also allow users to make forecasts of future conditions, as well as “hindcasts” — retroactive calculations of past trends and conditions.
     
  • News highlights and feature stories with strong visual elements that explore the findings of sea level researchers in detail.
     
  • An extensive library of published papers on sea level-related topics, hyperlinked to individual citations throughout “Understanding Sea Level.”
     
  • A multimedia section with dynamic still and video imagery, and a glossary of sea level terms.

  • A “frequently asked questions” section maintained by sea level scientists. Users can submit questions to scientists and data managers.


The website is optimized for most mobile devices, including smartphones and tablets.

“Sea Level Change: Observations from Space” is managed by a team led by JPL scientist Carmen Boening. The team is part of the NASA Sea Level Change Team research group. 

“With sea levels rising globally, as observed by satellites over the past decades, sea level change is a hot topic in climate research,” Boening said. “This new tool provides a NASA resource for researchers and a wealth of information for members of the public seeking a deeper understanding of sea level change.”

For more information on NASA’s Earth science activities, visit: http://www.nasa.gov/earth and http://climate.nasa.gov

JPL is a division of the California Institute of Technology in Pasadena.

 

 

 

 

 

NASA, Japan Make ASTER Earth Data Available At No Cost

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In March 2016, ASTER captured the eruption of Nicaragua’s Momotombo volcano with its visible and thermal infrared bands. The ash plume is depicted by the visible bands in blue-gray; the thermal infrared bands show hot lava flows in yellow and the active summit crater in white. Vegetation is red. Credit: NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team

Beginning today, all Earth imagery from a prolific Japanese remote sensing instrument operating aboard NASA’s Terra spacecraft since late 1999 is now available to users everywhere at no cost.

The public will have unlimited access to the complete 16-plus-year database for Japan’s Ministry of Economy, Trade and Industry (METI) Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument, which images Earth to map and monitor the changing surface of our planet. ASTER’s database currently consists of more than 2.95 million individual scenes. The content ranges from massive scars across the Oklahoma landscape from an EF-5 tornado and the devastating aftermath of flooding in Pakistan, to volcanic eruptions in Iceland and wildfires in California.

Previously, users could access ASTER’s global digital topographic maps of Earth online at no cost, but paid METI a nominal fee to order other ASTER data products. 

In announcing the change in policy, METI and NASA cited ASTER’s longevity and continued strong environmental monitoring capabilities. Launched in 1999, ASTER has far exceeded its five-year design life and will continue to operate for the foreseeable future as part of the suite of five Earth-observing instruments on Terra.

“We anticipate a dramatic increase in the number of users of our data, with new and exciting results to come,” said Michael Abrams, ASTER science team leader at NASA’s Jet Propulsion Laboratory in Pasadena, California, home to ASTER’s U.S. science team. ASTER data are processed into products using algorithms developed at JPL and the National Institute of Advanced Industrial Science and Technology (AIST) in Japan. A joint U.S./Japan science team validates and calibrates the instrument and data products.

ASTER is used to create detailed maps of land surface temperature, reflectance and elevation. The instrument acquires images in visible and thermal infrared wavelengths, with spatial resolutions ranging from about 50 to 300 feet (15 to 90 meters). ASTER data cover 99 percent of Earth’s landmass and span from 83 degrees north latitude to 83 degrees south. A single downward-looking ASTER scene covers an area on the ground measuring about 37-by-37 miles (60-by-60-kilometers).

ASTER uses its near-infrared spectral band and downward- and backward-viewing telescopes to create stereo-pair images, merging two slightly offset two-dimensional images to create the three-dimensional effect of depth. Each elevation measurement point in the data is 98 feet (30 meters) apart.

The broad spectral coverage and high spectral resolution of ASTER provide scientists in numerous disciplines with critical information for surface mapping and monitoring of dynamic conditions and changes over time. Example applications include monitoring glacial advances and retreats, monitoring potentially active volcanoes, identifying crop stress, determining cloud morphology and physical properties, evaluating wetlands, monitoring thermal pollution, monitoring coral reef degradation, mapping surface temperatures of soils and geology, and measuring surface heat balance.

ASTER data are now available via electronic download from NASA’s Land Processes Distributed Active Archive Center (LP DAAC) at the U.S. Geological Survey’s (USGS) Earth Resources Observation and Science Center in Sioux Falls, South Dakota, and from AIST. To access the data, visit: https://lpdaac.usgs.gov/dataset_discovery/aster or https://gbank.gsj.jp/madas/

NASA uses the vantage point of space to increase our understanding of our home planet, improve lives and safeguard our future. NASA develops new ways to observe and study Earth’s interconnected natural systems with long-term data records. The agency freely shares this unique knowledge and works with institutions around the world to gain new insights into how our planet is changing.

For more information about ASTER, visit: http://asterweb.jpl.nasa.gov/

For more information on NASA’s Terra mission, visit: http://terra.nasa.gov

For more information about NASA’s Earth science activities, visit: http://www.nasa.gov/earth

A Still-Growing El Niño Set to Bear Down on US

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The latest satellite image of Pacific sea surface heights from Jason-2 (left) differs slightly from one 18 years ago from Topex/Poseidon (right). In Dec. 1997, sea surface height was more intense and peaked in November. This year the area of high sea levels is less intense but considerably broader. (Credit: NASA/JPL-Caltech)

 


The current strong El Niño brewing in the Pacific Ocean shows no signs of waning, as seen in the latest satellite image from the U.S./European Ocean Surface Topography Mission (OSTM)/Jason-2 mission. 

El Niño 2015 has already created weather chaos around the world. Over the next few months, forecasters expect the United States to feel its impacts as well. 

The latest Jason-2 image bears a striking resemblance to one from December 1997, by Jason-2’s predecessor, the NASA/Centre National d’Etudes Spatiales (CNES) Topex/Poseidon mission, during the last large El Niño event. Both reflect the classic pattern of a fully developed El Niño. The images can be viewed at:

http://sealevel.jpl.nasa.gov/elnino2015/index.html

The images show nearly identical, unusually high sea surface heights along the equator in the central and eastern Pacific: the signature of a big and powerful El Niño. Higher-than-normal sea surface heights are an indication that a thick layer of warm water is present.

El Niños are triggered when the steady, westward-blowing trade winds in the Pacific weaken or even reverse direction, triggering a dramatic warming of the upper ocean in the central and eastern tropical Pacific. Clouds and storms follow the warm water, pumping heat and moisture high into the overlying atmosphere. These changes alter jet stream paths and affect storm tracks all over the world.

This year’s El Niño has caused the warm water layer that is normally piled up around Australia and Indonesia to thin dramatically, while in the eastern tropical Pacific, the normally cool surface waters are blanketed with a thick layer of warm water. This massive redistribution of heat causes ocean temperatures to rise from the central Pacific to the Americas. It has sapped Southeast Asia’s rain in the process, reducing rainfall over Indonesia and contributing to the growth of massive wildfires that have blanketed the region in choking smoke. 

El Niño is also implicated in Indian heat waves caused by delayed monsoon rains, as well as Pacific island sea level drops, widespread coral bleaching that is damaging coral reefs, droughts in South Africa, flooding in South America and a record-breaking hurricane season in the eastern tropical Pacific. Around the world, production of rice, wheat, coffee and other crops has been hit hard by droughts and floods, leading to higher prices. 

In the United States, many of El Niño’s biggest impacts are expected in early 2016. Forecasters at the National Oceanic and Atmospheric Administration favor an El Niño-induced shift in weather patterns to begin in the near future, ushering in several months of relatively cool and wet conditions across the southern United States, and relatively warm and dry conditions over the northern United States. The latest El Niño forecast from NOAA’s Climate Prediction Center is at: http://www.cpc.ncep.noaa.gov/

While scientists still do not know precisely how the current El Niño will affect the United States, the last large El Niño in 1997-98 was a wild ride for most of the nation. The “Great Ice Storm” of January 1998 crippled northern New England and southeastern Canada, but overall, the northern tier of the United States experienced long periods of mild weather and meager snowfall. Meanwhile, across the southern United States, a steady convoy of storms slammed most of California, moved east into the Southwest, drenched Texas and — pumped up by the warm waters of the Gulf of Mexico — wreaked havoc along the Gulf Coast, particularly in Florida. 

“In 2014, the current El Niño teased us — wavering off and on,” said Josh Willis, project scientist for the Jason missions at JPL. “But in early 2015, atmospheric conditions changed, and El Niño steadily expanded in the central and eastern Pacific. Although the sea surface height signal in 1997 was more intense and peaked in November of that year, in 2015, the area of high sea levels is larger. This could mean we have not yet seen the peak of this El Niño.”

During normal, non-El Niño conditions, the amount of warm water in the western equatorial Pacific is so large that sea levels are about 20 inches (50 centimeters) higher in the western Pacific than in the eastern Pacific. “You can see it in the latest Jason-2 image of the Pacific,” said Willis. “The 8-inch [20-centimeter] drop in the west, coupled with the 10-inch [25-centimeter] rise in the east, has completely wiped out the tilt in sea level we usually have along the equator.”

The new Jason-2 image shows that the amount of extra-warm surface water from the current El Niño (depicted in red and white shades) has continuously increased, especially in the eastern Pacific within 10 degrees latitude north and south of the equator. In the western Pacific, the area of low sea level (blue and purple) has decreased somewhat from late October. The white and red areas indicate unusual patterns of heat storage. In the white areas, the sea surface is between 6 and 10 inches (15 to 25 centimeters) above normal, while in the red areas, it is about 4 inches (10 centimeters) above normal. The green areas indicate normal conditions. The height of the ocean water relates, in part, to its temperature, and is an indicator of the amount of heat stored in the ocean below. 

Within this area, surface temperatures are greater than 86 degrees Fahrenheit (30 degrees Celsius) in the central equatorial Pacific and near 70 degrees Fahrenheit (21 degrees Celsius) off the coast of the Americas. This El Niño signal encompasses a surface area of 6 million square miles (16 million square kilometers) — more than twice as big as the continental United States. 

While no one can predict the exact timing or intensity of U.S. El Niño impacts, for drought-stricken California and the U.S. West, it’s expected to bring some relief. 

“The water story for much of the American West over most of the past decade has been dominated by punishing drought,” said JPL climatologist Bill Patzert. “Reservoir levels have fallen to record or near-record lows, while groundwater tables have dropped dangerously in many areas. Now we’re preparing to see the flip side of nature’s water cycle — the arrival of steady, heavy rains and snowfall.” 

In 1982-83 and 1997-98, large El Niños delivered about twice the average amount of rainfall to Southern California, along with mudslides, floods, high winds, lightning strikes and high surf. But Patzert cautioned that El Niño events are not drought busters. “Over the long haul, big El Niños are infrequent and supply only seven percent of California’s water,” he said.

“Looking ahead to summer, we might not be celebrating the demise of this El Niño,” cautioned Patzert. “It could be followed by a La Niña, which could bring roughly opposite effects to the world’s weather.” 

La Niñas are essentially the opposite of El Niño conditions. During a La Niña episode, trade winds are stronger than normal, and the cold water that normally exists along the coast of South America extends to the central equatorial Pacific. La Niña episodes change global weather patterns and are associated with less moisture in the air over cooler ocean waters. This results in less rain along the coasts of North and South America and along the central and eastern equatorial Pacific, and more rain in the far Western Pacific.

El Niño events are part of the long-term, evolving state of global climate, for which measurements of sea surface height are a key indicator. 

For an animation of the evolution of the 2015 and 1997 El Niños, visit: https://sealevel.jpl.nasa.gov/elnino2015/2015-animated.gif

For more information on how NASA studies El Niño, visit: http://climatesciences.jpl.nasa.gov/enso

To learn more about NASA’s satellite altimetry programs, visit: http://sealevel.jpl.nasa.gov

For more information about NASA’s Earth science activities, visit: http://www.nasa.gov/earth

 

NASA Finds New Way to Track Ocean Currents from Space

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NASA’s GRACE satellites (artist’s concept) measured Atlantic Ocean bottom pressure as an indicator of deep ocean current speed. In 2009, this pattern of above-average (blue) and below-average (red) seafloor pressure revealed a temporary slowing of the deep currents. Image credit: NASA/JPL-Caltech

A team of NASA and university scientists has developed a new way to use satellite measurements to track changes in Atlantic Ocean currents, which are a driving force in global climate. The finding opens a path to better monitoring and understanding of how ocean circulation is changing and what the changes may mean for future climate.

In the Atlantic, currents at the ocean surface, such as the Gulf Stream, carry sun-warmed water from the tropics northeastward. As the water moves through colder regions, it sheds its heat. By the time it gets to Greenland, it’s so cold and dense that it sinks a couple of miles down into the ocean depths. There it turns and flows back south. This open loop of shallow and deep currents is known to oceanographers as the Atlantic Meridional Overturning Circulation (AMOC) — part of the “conveyor belt” of ocean currents circulating water, heat and nutrients around the globe and affecting climate.

Because the AMOC moves so much heat, any change in it is likely to be an important indicator of how our planet is responding to warming caused by increasing greenhouse gases. In the last decade, a few isolated measurements have suggested that the AMOC is slowing down and moving less water. Many researchers are expecting the current to weaken as a consequence of global warming, but natural variations may also be involved. To better understand what is going on, scientists would like to have consistent observations over time that cover the entire Atlantic

“This [new] satellite approach allows us to improve projections of future changes and — quite literally — get to the bottom of what drives ocean current changes,” said Felix Landerer of NASA’s Jet Propulsion Laboratory, Pasadena, California, who led the research team.

Landerer and his colleagues used data from the twin satellites of NASA’s Gravity Recovery and Climate Experiment (GRACE) mission. Launched in 2002, GRACE provides a monthly record of tiny changes in Earth’s gravitational field, caused by changes in the amount of mass below the satellites. The mass of Earth’s land surfaces doesn’t change much over the course of a month; but the mass of water on or near Earth’s surface does, for example, as ice sheets melt and water is pumped from underground aquifers. GRACE has proven invaluable in tracking these changes.

At the bottom of the atmosphere — on Earth’s surface — changes in air pressure (a measure of the mass of the air) tell us about flowing air, or wind. At the bottom of the ocean, changes in pressure tell us about flowing water, or currents. Landerer and his team developed a way to isolate in the GRACE gravity data the signal of tiny pressure differences at the ocean bottom that are caused by changes in the deep ocean currents.

“We’ve wanted to observe this phenomenon with GRACE since we launched 13 years ago, but it took us this long to figure out how to squeeze the information out of the data stream,” said Michael Watkins, director of the Center for Space Research at the University of Texas at Austin, former GRACE project scientist and a co-author of the study.

The squeezing process required some very advanced data processing, but not as many data points as one might think. “In principle, you’d think you’d have to measure every 10 yards or so across the ocean to know the whole flow,” Landerer explained. “But in fact, if you can measure the farthest eastern and western points very accurately, that’s all you need to know how much water is flowing north and south in the entire Atlantic at that section. That theory has long been known and is exploited in buoy networks, but this is the first time we’ve been able to do it successfully from space.”

The new measurements agreed well with estimates from a network of ocean buoys that span the Atlantic Ocean near 26 degrees north latitude, operated by the Rapid Climate Change (RAPID) group at the U.K.’s National Oceanography Centre, Southampton. The agreement gives the researchers confidence that the technique can be expanded to provide estimates throughout the Atlantic. In fact, the GRACE measurements showed that a significant weakening in the overturning circulation, which the buoys recorded in the winter of 2009-10, extended several thousand miles north and south of the buoys’ latitude.

Gerard McCarthy, a research scientist in the RAPID group who was not involved with the study, said, “The results highlight synergies between [direct measurements] like [those from] RAPID and remote sensing — all the more important given the rapid and surprising changes occurring in the North Atlantic at the present time.” Eric Lindstrom, NASA’s Physical Oceanography Program manager at the agency’s headquarters in Washington, pointed out, “It’s awesome that GRACE can see variations of deep water transport, [but] this signal might never have been detected or verified without the RAPID array. We will continue to need both in situ and space-based systems to monitor the subtle but significant variations of the ocean circulation.”

A paper in the journal Geophysical Research Letters describing the new technique and first results is available online in prepublication form: http://onlinelibrary.wiley.com/doi/10.1002/2015GL065730/abstract?campaign=wolacceptedarticle

Halloween Skies to Include Dead Comet Flyby

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The large space rock that will zip past Earth this Halloween is most likely a dead comet that, fittingly, bears an eerie resemblance to a skull.

Scientists observing asteroid 2015 TB145 with NASA’s Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, have determined that the celestial object is more than likely a dead comet that has shed its volatiles after numerous passes around the sun.

The belated comet has also been observed by optical and radar observatories around the world, providing even more data, including our first close-up views of its surface. Asteroid 2015 TB145 will safely fly by our planet at just under 1.3 lunar distances, or about 302,000 miles (486,000 kilometers), on Halloween (Oct. 31) at 1 p.m. EDT (10 a.m. PDT, 17:00 UTC).

The first radar images of the dead comet were generated by the National Science Foundation’s 305-meter (1,000-foot) Arecibo Observatory in Puerto Rico. The radar images from Arecibo indicate the object is spherical in shape and approximately 2,000 feet (600 meters) in diameter and completes a rotation about once every five hours. 

“The IRTF data may indicate that the object might be a dead comet, but in the Arecibo images it appears to have donned a skull costume for its Halloween flyby,” said Kelly Fast, IRTF program scientist at NASA Headquarters and acting program manager for NASA’s NEO Observations Program.

These first radar images from the National Science Foundation’s 1,000-foot (305-meter) Arecibo Observatory in Puerto Rico, indicate the near-Earth object is spherical in shape and approximately 2,000 feet (600 meters) in diameter. The radar images were taken on Oct. 30, 2015, and the image resolution is 25 feet (7.5 meters) per pixel.Image credit: NAIC-Arecibo/NSF

Managed by the University of Hawaii for NASA, the IRTF’s 3-meter (10 foot) telescope collected infrared data on the object. The data may finally put to rest the debate over whether 2015 TB145, with its unusual orbit, is an asteroid or is of cometary origin.

“We found that the object reflects about six percent of the light it receives from the sun,” said Vishnu Reddy, a research scientist at the Planetary Science Institute, Tucson, Arizona. “That is similar to fresh asphalt, and while here on Earth we think that is pretty dark, it is brighter than a typical comet which reflects only 3 to 5 percent of the light. That suggests it could be cometary in origin — but as there is no coma evident, the conclusion is it is a dead comet.”

Radar images generated by the Arecibo team are available at:

https://www.facebook.com/notes/national-astronomy-and-ionosphere-center-arecibo-observatory/near-earth-asteroid-2015-tb145-passes-by-without-a-fright/1082765941733673

Asteroid 2015 TB145 was discovered on Oct. 10, 2015, by the University of Hawaii’s Pan-STARRS-1 (Panoramic Survey Telescope and Rapid Response System) on Haleakala, Maui, part of the NASA-funded Near-Earth Object Observations (NEOO) Program. The next time the asteroid will be in Earth’s neighborhood will be in September 2018, when it will make a distant pass at about 24 million miles (38 million kilometers), or about a quarter the distance between Earth and the sun.

Radar is a powerful technique for studying an asteroid’s size, shape, rotation, surface features and surface roughness, and for improving the calculation of asteroid orbits. Radar measurements of asteroid distances and velocities often enable computation of asteroid orbits much further into the future than would be possible otherwise.

NASA places a high priority on tracking asteroids and protecting our home planet from them. In fact, the U.S. has the most robust and productive survey and detection program for discovering near-Earth objects (NEOs). To date, U.S.-funded assets have discovered over 98 percent of the known NEOs.

In addition to the resources NASA puts into understanding asteroids, it also partners with other U.S. government agencies, university-based astronomers, and space science institutes across the country, often with grants, interagency transfers and other contracts from NASA, and also with international space agencies and institutions that are working to track and better understand these objects. In addition, NASA values the work of numerous highly skilled amateur astronomers, whose accurate observational data helps improve asteroid orbits after they are found.

NASA’s Jet Propulsion Laboratory, Pasadena, California, hosts the Center for Near-Earth Object Studies for NASA’s Near-Earth Object Observations Program within the agency’s Science Mission Directorate.

More information about asteroids and near-Earth objects is at these websites:

http://neo.jpl.nasa.gov

http://www.jpl.nasa.gov/asteroidwatch

 

 

NASA Spots the ‘Great Pumpkin’: Halloween Asteroid a Treat for Radar Astronomers

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This is a graphic depicting the orbit of asteroid 2015 TB145. The asteroid will safely fly past Earth slightly farther out than the moon’s orbit on Oct. 31 at 10:05 a.m. Pacific (1:05 p.m. EDT and 17:05 UTC). Image credit: NASA/JPL-Caltech

NASA scientists are tracking the upcoming Halloween flyby of asteroid 2015 TB145 with several optical observatories and the radar capabilities of the agency’s Deep Space Network at Goldstone, California. The asteroid will fly past Earth at a safe distance slightly farther than the moon’s orbit on Oct. 31 at 10:01 a.m. PDT (1:01 p.m. EDT). Scientists are treating the flyby of the estimated 1,300-foot-wide (400-meter) asteroid as a science target of opportunity, allowing instruments on “spacecraft Earth” to scan it during the close pass.

Published on Oct 29, 2015JPL scientist Marina Brozovic explains how radar will be used to study asteroid 2015 TB145 when it safely passes Earth on Oct. 31, 2015. Scientists are tracking the Halloween flyby with several optical observatories and the radar capabilities of the agency’s Deep Space Network at Goldstone, California. Radar images should be available within a few days of the flyby. The asteroid will fly past Earth at a safe distance slightly farther than the moon’s orbit on Oct. 31 at 10:01 a.m. PDT (1:01 p.m. EDT). Scientists are treating the flyby of the estimated 1,300-foot-wide (400-meter) asteroid as a science target of opportunity. 

Asteroid 2015 TB145 was discovered on Oct. 10, 2015, by the University of Hawaii’s Pan-STARRS-1 (Panoramic Survey Telescope and Rapid Response System) on Haleakala, Maui, part of the NASA-funded Near-Earth Object Observation (NEOO) Program. According to the catalog of near-Earth objects (NEOs) kept by the Minor Planet Center, this is the closest currently known approach by an object this large until asteroid 1999 AN10, at about 2,600 feet (800 meters) in size, approaches at about 1 lunar distance (238,000 miles from Earth) in August 2027.

“The trajectory of 2015 TB145 is well understood,” said Paul Chodas, manager of the Center for Near Earth Object Studies at NASA’s Jet Propulsion Laboratory, Pasadena, California. “At the point of closest approach, it will be no closer than about 300,000 miles — 480,000 kilometers or 1.3 lunar distances. Even though that is relatively close by celestial standards, it is expected to be fairly faint, so night-sky Earth observers would need at least a small telescope to view it.

The gravitational influence of the asteroid is so small it will have no detectable effect on the moon or anything here on Earth, including our planet’s tides or tectonic plates

The Center for NEO Studies at JPL is a central node for NEO data analysis in NASA’s Near-Earth Object Observation Program and a key group involved with the international collaboration of astronomers and scientists who keep watch on the sky with their telescopes, looking for asteroids that could be a hazard to impact our planet and predicting their paths through space for the foreseeable future

“The close approach of 2015 TB145 at about 1.3 times the distance of the moon’s orbit, coupled with its size, suggests it will be one of the best asteroids for radar imaging we’ll see for several years,” said Lance Benner, of JPL, who leads NASA’s asteroid radar research program. “We plan to test a new capability to obtain radar images with two-meter resolution for the first time and hope to see unprecedented levels of detail.”

During tracking, scientists will use the 34-meter (110-foot) DSS 13 antenna at Goldstone to bounce radio waves off the asteroid. Radar echoes will in turn be collected by the National Radio Astronomy Observatory’s Green Bank Telescope in Green Bank, West Virginia, and the National Astronomy and Ionosphere Center’s Arecibo Observatory, Puerto Rico. NASA scientists hope to obtain radar images of the asteroid as fine as about 7 feet (2 meters) per pixel. This should reveal a wealth of detail about the object’s surface features, shape, dimensions and other physical properties

“The asteroid’s orbit is very oblong with a high inclination to below the plane of the solar system,” said Benner. “Such a unique orbit, along with its high encounter velocity — about 35 kilometers or 22 miles per second — raises the question of whether it may be some type of comet. If so, then this would be the first time that the Goldstone radar has imaged a comet from such a close distance.”

NASA’s Near-Earth Object Observations Program detects, tracks and characterizes asteroids and comets passing within 30 million miles of Earth using both ground- and space-based telescopes. The NEOO Program, sometimes called “Spaceguard,” discovers these objects, characterizes the physical nature of a subset of them, and predicts their paths to determine if any could be potentially hazardous to our planet. There are no known credible impact threats to date — only the ongoing and harmless in-fall of meteoroids, tiny asteroids that burn up in the atmosphere

JPL hosts the Center for Near-Earth Object Studies for NASA’s Near-Earth Object Observations Program within the agency’s Science Mission Directorate. JPL is a division of the California Institute of Technology in Pasadena.

More information about asteroids and near-Earth objects is at:  http://neo.jpl.nasa.gov and http://www.jpl.nasa.gov/asteroidwatch

Excitement Grows as NASA Carbon Sleuth Begins Year Two

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Global average carbon dioxide concentrations as seen by NASA's Orbiting Carbon Observatory-2 mission, June 1-15, 2015. OCO-2 measures carbon dioxide from the top of Earth's atmosphere to its surface. Higher carbon dioxide concentrations are in red, with lower concentrations in yellows and greens. Credit: NASA/JPL-Caltech
Global average carbon dioxide concentrations as seen by NASA’s Orbiting Carbon Observatory-2 mission, June 1-15, 2015. OCO-2 measures carbon dioxide from the top of Earth’s atmosphere to its surface. Higher carbon dioxide concentrations are in red, with lower concentrations in yellows and greens. Credit: NASA/JPL-Caltech

Scientists busy poring over more than a year of data from NASA’s Orbiting Carbon Observatory-2 (OCO-2) mission are seeing patterns emerge as they seek answers to the science questions that drive the mission.

Launched in July 2014, OCO-2, an experimental carbon-dioxide measurement mission, is designed to give the international science community a new view of the global carbon cycle in unprecedented detail. During its two-year primary mission, the satellite observatory is tracking the large-scale movement of carbon between Earth’s atmosphere, its plants and soil, and the ocean, from season to season and from year to year. OCO-2 began routine science operations in September 2014.

“We can already clearly see patterns of seasonal change and variations in carbon dioxide around the globe,” said Annmarie Eldering, OCO-2 deputy project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. “Far more subtle features are expected to emerge over time.”

A new animation depicting the first full year of OCO-2 science operations is available at:

Armed with a full annual cycle of data, OCO-2 scientists are now beginning to study the net sources of carbon dioxide as well as their “sinks” — places in the Earth system that store carbon, such as the ocean and plants on land. This information will help scientists better understand the natural processes currently absorbing more than half the carbon dioxide emitted into the atmosphere by human activities. This is a key to understanding how Earth’s climate may change in the future as greenhouse gas concentrations increase.

The first year of data from the mission reveals a portrait of a dynamic, living planet. Between mid-May and mid-July 2015, OCO-2 saw a dramatic reduction in the abundance of atmospheric carbon dioxide across the northern hemisphere, as plants on land sprang to life and began rapidly absorbing carbon dioxide from the air to form new leaves, stems and roots.

During this intense, two-month period, known as the “spring drawdown,” OCO-2 measurements show the concentration of atmospheric carbon dioxide over much of the northern hemisphere decreased by two to three percent. That’s 8 to 12 parts per million out of the global average background concentration of 400 parts per million.

“That’s a big but expected change,” said Eldering.

“This is the first time we’ve ever had the opportunity to observe the spring drawdown across the entire northern hemisphere with this kind of spatial resolution, seeing changes from week to week.”

Also as expected, OCO-2 data show increased concentrations of carbon dioxide associated with human activities. Higher carbon dioxide levels of several parts per million are seen in regions where fossil fuels are being consumed by large power plants or megacities. Enhanced levels are also seen in the Amazon, Central Africa and Indonesia, where forests are being cleared and burned to create fields for agricultural use.

Researchers Abhishek Chatterjee of the Global Modeling and Assimilation Office at NASA’s Goddard Space Flight Center, Greenbelt, Maryland; and Michelle Gierach and Dave Schimel of JPL are investigating a strong correlation observed between atmospheric carbon dioxide over the Pacific Ocean and the current El Nino.

Fluctuations in carbon dioxide appear to be strongly linked with warmer sea surface temperatures. OCO-2’s unprecedented density of measurements is giving researchers a unique data set to understand and separate the roles that sea surface temperatures, winds, regional emissions and other variables may be playing in the carbon dioxide concentrations.

“We believe 2016 will see breakthrough OCO-2 research results, as scientists work to unravel the mysteries of finding carbon dioxide sources and natural sinks,” said Eldering.

Through most of OCO-2’s first year in space, the mission team was busy calibrating its science instrument, learning how to process its massive amount of data, and delivering data products to NASA’s Goddard Earth Sciences Data and Information Services Center (GES-DISC) in Greenbelt, Maryland, for distribution to the world’s science community.

Scientists are comparing OCO-2 data to ground-based measurements to validate the satellite data and tie it to internationally accepted standards for accuracy and precision.

Routine delivery of OCO-2 data — calibrated spectra of reflected sunlight that reveal the fingerprints of carbon dioxide — began in late 2014, while estimates of carbon dioxide derived from cloud-free OCO-2 observations have been delivered since March 2015. Recently, the OCO-2 team reprocessed the OCO-2 data set to incorporate improvements in instrument calibration and correct other known issues with the original data release.

Every day, OCO-2 orbits Earth 14.5 times and collects and returns about a million measurements. After eliminating data contaminated by clouds, aerosols and steep terrain, between 10 to 13 percent of the measurements are of sufficient quality to derive accurate estimates of the average carbon dioxide concentration between Earth’s surface and space. That’s at least 100 times more carbon dioxide measurements than from all other sources of precise carbon dioxide data combined.

NASA uses the vantage point of space to increase our understanding of our home planet, improve lives and safeguard our future. NASA develops new ways to observe and study Earth’s interconnected natural systems with long-term data records. The agency freely shares this unique knowledge and works with institutions around the world to gain new insights into how our planet is changing.

For more information on OCO-2, visit: http://www.nasa.gov/oco-2

For more information about NASA’s Earth science activities, visit: http://www.nasa.gov/earth