National Aeronautics and Space Administration Ocean Surface Topography Mission/Jason-2 Watching Over Our Ocean Acknowledgments Please call the Public Affairs Offices at NASA, NOAA, CNES or EUMETSAT before contacting individual scientists at these organizations. NASA Jet Propulsion Laboratory Alan Buis, 818-354-0474, [email protected] NASA Headquarters Steve Cole, 202-358-0918, [email protected] NASA Kennedy Space Center George Diller, 321-867-2468, [email protected] NOAA Environmental Satellite, Data and Information Service John Leslie, 301-713-2087, x174, [email protected] CNES Eliane Moreaux, 011-33-5-61-27-33-44, [email protected] EUMETSAT Claudia Ritsert-Clark, 011-49-6151-807-609, [email protected] NASA Web sites http://www.nasa.gov/ostm http://sealevel.jpl.nasa.gov/mission/ostm.html NOAA Web site http://www.osd.noaa.gov/ostm/index.htm CNES Web site http://www.aviso.oceanobs.com/en/missions/future-missions/jason-2/index.html EUMETSAT Web site http://www.eumetsat.int/Home/Main/What_We_Do/Satellites/Jason/index.htm?l=en Content: Nicole Miklus Design: Sally J. Bensusen Editing: Alan D. Buis, Annie Richardson, Margaret Srinivasan, Rosemary Sullivant, Alan Ward Cover image: NASA, CNES Table of Contents The Ocean in a Changing Climate ................................................ 4 Mapping the Ocean ...................................................................... 6 A Satellite Altimetry Family Tree .................................................. 8 TOPEX/Poseidon and Jason-1: Lessons Learned ........................... 11 OSTM/Jason-2: Continuing the Altimetry Legacy ........................ 12 How It All Works: The “Nuts and Bolts” of OSTM/Jason-2 .......... 13 The Instruments ............................................................................ 14 OSTM/Jason-2: How Is It Different? ............................................ 16 The Future: Jason-3 and Beyond ................................................... 17 OSTM/Jason-2 Science Team ...................................................... 18 The Ocean in a Changing Climate We see it on the evening news; we witness it in continue to change, it is first necessary to our own backyards—our climate is changing. understand what drives it. From heat waves to more devastating floods and hurricanes to melting glaciers and sea The Ocean’s Role in Climate level rise, the effects of climate change are all around us. The vitality of crops, our drinking The ocean is one of the biggest “drivers” of water supply, animal populations, the spread Earth’s climate system. Global climate is the of diseases, and, ultimately, the rise and fall result of a complex interplay between the of civilizations are all influenced by climate. atmosphere and ocean. The world ocean Scientists know that natural variability in stores immense amounts of heat—much more Earth’s climate affects weather patterns, but than the atmosphere—and recirculates this it’s also increasingly clear that the burning of energy around the planet in a process called fossil fuels by humans is a major contributor to the oceanic heat conveyor belt. The ocean cov- the changes we are experiencing. ers more than 70 percent of Earth’s surface During the last century, carbon dioxide and absorbs a large amount of the energy our emissions caused by human activities have planet receives from the Sun. Solar energy been the main contributor to the 0.6ºC (1ºF) is not distributed evenly over the surface, increase in Earth’s average global air tempera- though. Equatorial regions receive more solar ture—a seemingly small amount, but enough radiation than they emit back to space, while to cause global environmental impacts. It is polar regions emit more radiation than they unclear, though, how much warming will receive from the Sun. The ocean, along with occur in the future and how widespread it the atmosphere, helps to move heat between will be. To predict how Earth’s climate will the equator and the poles. 65 Image credit: WH Films 45 The image at right shows 25 the dominant patterns for the change of sea level of the global ocean from 5 1992 to 2008. The yel- low and red regions illus- -5 trate that over most of the ocean, the sea level is ris- ing at rates from 1-10 mil- -25 limeters per year. The pat- terns of sea level rise are not uniform and are deter- mined by the ocean circu- -45 lation and the processes 0 30 60 90 120 150 180 210 240 270 300 330 360 through which heat is ab- sorbed and transported -65 Sea Level Anomaly (millimeters/year) by the ocean. Credit: L. Fu, NASA JPL -10 -6 -2 2 6 10 4 OSTM I Watching Over Our Ocean Salinity (PSU) 32 34 36 38 Atmospheric winds blow across the ocean water vapor—the most abundant greenhouse The oceanic heat conveyor surface to create currents that swirl in gyres gas and one that’s 50 times as powerful as belt is also known as the Thermohaline Circulation. around areas of high and low sea level. These carbon dioxide—into the atmosphere. At the Thermohaline because currents release heat as they travel from the same time, warmer ocean temperatures cause these surface and deep currents are driven both by equator to the poles, and some of this heat the ocean’s volume to increase in a process heat (“thermo”) and salinity is transferred to the atmosphere through called thermal expansion. The result is higher (“haline”). It is estimated that the round trip journey evaporation over tropical and subtropical sea levels that threaten coastal communities of a single section of this waters. As the currents lose heat, they begin and habitats. While we don’t know exactly conveyor belt can take from 1,000 to 2,000 years. Im- to cool and become more dense, slowly sink- how much more heat the ocean can absorb age credit: NASA, adapted ing and spreading throughout the deep parts from global warming, it is already clear that from the IPCC 2001 and of the ocean. Eventually, they will reach the significant changes in Earth’s hydrologic Rahmstorf 2002. surface once again and perpetuate the cycle in cycle and climate result from any excess stor- Note: PSU stands for this oceanic heat conveyor belt. In this way, age of heat. Practical Salinity Unit. One PSU is approximately the ocean regulates the temperature on our With the evaporation rate higher, scientists equivalent to 1 gram of planet much like the thermostat in your home sea salt per kilogram of have found that the salinity of the ocean acts to warm or cool your surroundings. seawater. is changing. Water in the polar regions is The Ocean and Rising Temperatures becoming fresher, while tropical waters are getting saltier. Changes in the salinity of the As global temperature rises, the excess heat ocean can disrupt its circulation patterns, is absorbed and stored in the upper layers of stalling the movement of heat and leading the ocean—a process that slows atmospheric to global or regional cooling within several warming. More than 80 percent of the heat decades. Earth has experienced these abrupt from global warming over the past 50 years climate changes throughout its history, with has been absorbed by the ocean. This heat, the most recent one—known as the Little Ice however, is not stored without consequence. Age—triggered about 700 years ago. Charting Increased sea surface temperatures cause the behavior of the ocean over time allows us evaporation to intensify, introducing more to better foresee changes in Earth’s climate. OSTM I Watching Over Our Ocean 5 Mapping the Ocean Ocean Surface Topography Altimetry The ocean surface has highs and lows, just The height of the sea surface is measured like the hills and valleys of Earth’s land with satellite altimetry. Radar altimeters depicted on a topographic map. The variations measure the distance between the satellite in height, called ocean surface topography, can and the sea surface by calculating the time it be as much as 2 meters (6.5 feet) from place takes for a microwave pulse to reach the sea to place. surface and travel back to the satellite. Earth’s gravity field imposes a greater influence The measurements are corrected to account on sea surface height. By causing the sea for anything that may delay the microwave surface to assume an irregular shape called pulses, such as water vapor in the lower the geoid, gravity is responsible for height atmosphere, free electrons in the upper at- differences of up to 200 meters (656 feet). mosphere (ionosphere), and the dry air mass Ocean surface topography is determined by of the atmosphere. The result is remarkably removing the effect of Earth’s gravity from precise sea surface levels—to within a few the total sea surface height to reveal the centimeters (about one inch) height. Image credit: Bo Qiu 2-meter variations caused by ocean circulation, temperature, and salt content. It is a valuable Measurements of wave height, ocean current indicator of the ocean’s role in our climate, velocity and direction, and wind speed can telling us where the ocean stores and trans- also be obtained using satellite altimetry. ports heat and how it interacts with the atmosphere. Accurate maps of ocean surface topog- raphy are crucial to understanding the ocean’s influence on our weather pat- Satellite radar altimeter terns and long-term measurements of ocean climate. The dramatic surface topography are greatly improved by impact that rising sea instruments that provide levels have on coastal precision orbit determi- nation. The Poseidon-3 regions is just one of altimeter on OSTM/Jason-2 many examples of is complemented by three such instruments: the how changes in the GPSP, LRA, and DORIS. ocean greatly affect (See The Instruments sec- tion on page 14.) Image our society. credit: NASA JPL 6 OSTM I Watching Over Our Ocean OSTM/Jason-2 map of sea level anomalies from July 4 to July 14, 2008.