Earth Science Studies
Written by Carol Rasmussen
NASA Earth Science News Team
- 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.
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.
- “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.
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
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.
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