U24B-01 INVITED 

Multi-disciplinary Applications of the Gravity Recovery And Climate Experiment (GRACE)

* Tapley, B (tapley@csr.utexas.edu), Center for Space Research, R1000 The University of Texas at Austin, Austin, TX 78712, United States Rothacher, M (rothacher@gfz-potsdam.de), GeoForschungsZentrum Potsdam, Telegraphenberg A 17, Potsdam, 14473, Germany Watkins, M (Michael.M.Watkins@jpl.nasa.gov), Jet Propulsion Laboratory, Mail Stop 301-125L 4800 Oak Grove Drive, Pasadena, CA 91109, United States Bettadpur, S (srinivas@csr.utexas.edu), Center for Space Research, R1000 The University of Texas at Austin, Austin, TX 78712, United States Flechtner, F (flechtne@gfz-potsdam.de), GeoForschungsZentrum Potsdam, Telegraphenberg A 17, Potsdam, 14473, Germany

The twin satellites involved in the joint NASA/DLR mission GRACE were launched on March 17, 2002 and initiated scientific measurements in May 2002. The mission completed a five-year measurement sequence in May 2007. The purpose of the GRACE mission is to measure the time-variability and long-term mean mass distribution of the Earth's dynamic system. During the five-year interval, GRACE has provided global measurements of mass flux between the land, ocean, atmosphere and the cryosphere with un-precedented detail and accuracy. During the 2007 year, a completed update of the background models and a reprocessing of the five-year data set was completed. This release referred to as RL 04 provides the basis for the latest data products. In this presentation, we will summarize the status of the mission and the improvements made in the Level 1 and Level 2 data products. Initial results from the RL04 evaluation and describe plans for future product evaluation, calibration and evolution. Finally, we will survey the state of the multi-disciplinary science applications of the GRACE mission that are being contemplated in conjunction with various satellite missions (TOPEX/Poseidon, Jason-1, ICESat, GOCE).

U24B-02 INVITED 

Secular Trends in GRACE Data

* Wahr, J (wahr@lemond.colorado.edu), University of Colorado, Department of Physics and CIRES, Boulder, CO 80309, United States Velicogna, I (isabella@lemond.colorado.edu), University of California at Irvine, Department of Earth System Science, Irvine, CA 92697, United States Swenson, S (swensosc@sunray3.cgd.ucar.edu), National Center for Atmospheric Research, Advanced Study Program, Boulder, CO 80307, United States

GRACE has now provided over five years of monthly gravity field solutions. During this time, analysis techniques have been steadily improving. And as more users have applied GRACE data to an increasing variety of geophysical problems, the capabilities and limitations of GRACE have become better understood. As the data span lengthens, secular trends emerge more clearly above shorter-period variability and become easier to identify. Here, we present a global survey of secular trends in the GRACE data. We show current results for such familiar signals as those caused by ice mass variations in Antarctica and Greenland, and by post glacial rebound in northern Canada and Scandinavia. We also show evidence of a number of smaller and lesser-known signals.

U24B-03 INVITED 

GRACE Applied to Terrestrial Hydrology

* Rodell, M (Matthew.Rodell@nasa.gov), NASA Goddard Space Flight Center, Hydrological Sciences Branch, Code 614.3, Greenebelt, MD 20771, United States Famiglietti, J S (jfamigli@uci.edu), University of California, Irvine, Earth System Science, Irvine, CA 92697, United States Zaitchik, B F (Benjamin.F.Zaitchik@nasa.gov), NASA Goddard Space Flight Center, Hydrological Sciences Branch, Code 614.3, Greenebelt, MD 20771, United States Zaitchik, B F (Benjamin.F.Zaitchik@nasa.gov), Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD 20742, United States Velicogna, I (isabella@giove.colorado.edu), University of California, Irvine, Earth System Science, Irvine, CA 92697, United States

The Gravity Recovery and Climate Experiment (GRACE) satellite mission is now providing regional-scale estimates of variations in terrestrial water storage (TWS; the sum of groundwater, soil moisture, surface water, and snow). The potential of GRACE to benefit hydroclimatological research and water resources assessments is enormous, because no other remote sensing technique is able to measure water stored below the first few centimeters of soil. However, because the spatial and temporal resolutions of GRACE derived TWS change maps are low relative to other hydrological observing systems, and because vertically-integrated TWS is a variable unfamiliar to hydrologists, realizing that potential has been a challenge. This presentation will discuss current and new hydrological applications of GRACE and recent advances which will enable more widespread use of GRACE data.

U24B-04 

Water Balance Studies Using GRACE

* Swenson, S C (swensosc@ucar.edu), National Center for Atmospheric Research, POBox 3000, Boulder, CO 80307, United States Berg, A (aberg@uoguelph.ca), University of Guelph, University of Guelph, Guelph, ON N1G 2W1, Canada Wahr, J (wahr@colorado.edu), University of Colorado, Boulder, CB390 University of Colorado, Boulder, CO 80309, United States

GRACE has provided estimates of vertically integrated water storage anomalies at monthly intervals with a useful spatial resolution of 300-500 km. While interesting in isolation, these data are perhaps most effectively applied in conjunction with other complementary datasets. In this presentation, we report on recent water balance studies combining GRACE data with in situ measurements of soil moisture, groundwater, and snow water equivalent.

U24B-05 

Influence of the Amazon Floodwave on the Intra-Basin Variability of GRACE Water Storage Estimates

Bates, P (paul.bates@bristol.ac.uk), School of Geographical Sciences, Bristol University, Bristol, UK 43210, Han, S (schan@puuoo.gsfc.nasa.gov), NASA Goddard Space Flight Center, NASA GSFC, Greenbelt, MD 43210, * Alsdorf, D (alsdorf.1@osu.edu), School of Earth Sciences, Ohio State University, Columbus, OH 43210, Seo, K (schan@puuoo.gsfc.nasa.gov), Korean Polar Research Institute, Korean Polar Research Institute, Incheon, 43210,

The water mass in the Amazon Basin consists largely of precipitation, which averages well over 2 m/yr and water stored on floodplains and in wetlands, which cover ~15% to 20% of the Basin. Our knowledge of this water mass is limited by a low spatial sampling and availability of stream flow and precipitation measurements. For example, published estimates of annual Amazon River discharge vary from ~150,000 to ~200,000 cubic-meters per second: a difference greater than twice the annual flow of the Mississippi. GRACE measurements are anticipated to help overcome this problem. While monthly GRACE gravity solutions are typically used to estimate the basin-wide average of the water storage variation, we analyze the spatial and temporal variability within the Amazon Basin by estimating the water storage directly from the raw satellite-tracking data. The spatial and temporal resolutions with this method are improved to 3x3 degrees and 15 days, respectively, allowing better quantification of the intra-basin variability. We analyzed equally spaced 3x3 degree regions along the mainstem Amazon River and along major tributaries flowing from the south and from the north. Our GRACE estimates of storage change are compared to precipitation from the Global Precipitation Climatology Project (GPCP), in-situ stream-gauge discharge, evaporation estimates, and remotely sensed measurements of flooded areas. We find that GRACE amplitudes compare well to GPCP based precipitation (P) minus model based evaporation (E), but precede the peak and trough P–E by a month. Changes in river channel discharge, measured as Qin minus Qout in each of the regions along the mainstem, account for this timing offset. The storage capacities of the floodplains and wetlands in those regions are sufficient to hold and release the water mass as estimated by GRACE.

U24B-06 

Recent land ice mass flux observations from GRACE mascon solutions and their connection to surface elevation change and melt data

* Luthcke, S B (Scott.B.Luthcke@nasa.gov), NASA GSFC, Greenbelt Rd., Greenbelt, MD 20770, United States Rowlands, D D (David.D.Rowlands@nasa.gov), NASA GSFC, Greenbelt Rd., Greenbelt, MD 20770, United States Zwally, H J (zwally@icesat2.gsfc.nasa.gov), NASA GSFC, Greenbelt Rd., Greenbelt, MD 20770, United States Hall, D (Dorothy.K.Hall@nasa.gov), NASA GSFC, Greenbelt Rd., Greenbelt, MD 20770, United States Arendt, A (arendt@icesat2.gsfc.nasa.gov), NASA GSFC, Greenbelt Rd., Greenbelt, MD 20770, United States Lemoine, F G (flemoine@puuoo.gsfc.nasa.gov), NASA GSFC, Greenbelt Rd., Greenbelt, MD 20770, United States McCarthy, J J (jmccarthy@sgt-inc.com), SGT Inc., Greenbelt Rd., Greenbelt, MD 20771, United States Williams, T A (twilliams03@carolina.rr.com), SGT Inc., Greenbelt Rd., Greenbelt, MD 20771, United States

Mass changes of the Earth's ice sheets and glacier systems are of considerable importance because of their sensitivity to climate change and their contribution to rising sea level. Recent changes in the cryosphere highlight the importance of methods for directly observing the complex spatial and temporal variation of land ice mass flux. Since its launch in March of 2002, the NASA/DLR Gravity Recovery and Climate Experiment (GRACE) mission has been acquiring ultra-precise inter-satellite K-band range and range-rate (KBRR) measurements enabling a direct mapping of static and time-variable gravity. These data provide new opportunities to observe and understand ice mass changes at unprecedented temporal and spatial resolutions. In order to improve upon the ice mass change observations derived from GRACE, we have employed unique data analysis approaches to obtain lumped harmonic local mass concentration solutions (mascon solutions) from GRACE inter-satellite range-rate measurements. We have computed multi-year time series of surface mass flux for Greenland and Antarctica coastal and interior ice sheet sub-drainage systems as well as the Alaskan glacier systems. These mascon solutions provide important observations of the seasonal and inter-annual evolution of the Earth's land ice. Additionally, these solutions facilitate a detailed comparison to surface elevation change observations from spaceborne and airborne laser altimetry as well as surface melt observations. We present our latest mascon solutions of the Greenland and Antarctica ice sheets as well as the Alaska mountain glaciers. We compare these mass flux solutions to ICESat and airborne laser altimeter observations of surface elevation change as well as surface melt observations derived from MODIS data. The combination of GRACE high-resolution mass flux observations together with the surface elevation change and surface melt observations is beginning to reveal a detailed understanding of the Earth's high latitude land ice evolution.

U24B-07 INVITED 

GRACE Applications to Ocean Circulation: a review of the first 5 years.

* Zlotnicki, V (VZlotnicki@jpl.nasa.gov), Jet Propulsion Laboratory California Institute of Technology, M/S 300-323 4800 Oak Grove Dr, Pasadena, CA 91109, United States

The nearly-5 year time series of subtle gravitational changes measured by GRACE, and its measurement of the time-averaged field, have provided new insights into the time-averaged and the time-varying oceanic circulation. Among these are interannual changes in the Arctic ocean and in the barotropic circulation of the Antarctic Circumpolar Current; when combined with radar altimetry, time changes in the heat content of the oceans become apparent, albeit at large spatial scales. The time-averaged geostrophic circulation is now much better constrained thanks to a unique combination of GRACE data, radar altimetry and surface float data. Assimilation of GRACE data into numerical models is now possible. Challenges also remain, especially at low latitudes, where the signals are weaker and the uncertainties larger. This presentation will provide a review of these results, a progress report in the application of GRACE data to ocean problems, and a set of challenges for future work.

U24B-08 

Closing the Globally Averaged Sea Level Budget on Seasonal to Interannual Time Scales

* Willis, J K (joshua.k.willis@jpl.nasa.gov), Jet Propulsion Laboratory California Institute of Technology, M/S 300-323 4800 Oak Grove Dr., Pasadena, CA 90034, United States Chambers, D P (chambers@csr.utexas.edu), Center for Space Research, University of Texas at Austin 3925 W. Braker Lane #200, Austin, TX 78759, United States Nerem, R S (Nerem@Colorado.EDU), Colorado Center for Astrodynamics Research, The University of Colorado Campus Box 431, Boulder, CO 80309, United States

Analysis of ocean temperature and salinity data from profiling floats along with satellite measurements of sea surface height and the time variable gravity field are used to investigate the causes of global mean sea level rise between mid-2003 and 2007. Between 2004 and 2006, the observed fluctuations in sea level can be explained as the sum of a mass component and a steric (or density related) component to within the error bounds of each observing system. During this period, sea level in 2005 was approximately 4 mm higher than in 2004 due primarily to a sudden increase in ocean mass in the early part of the year, with a negligible contribution from steric variability. The 3.5-year trends do not balance, however, suggesting that systematic errors remain in one or more of these observing systems.

Author(s) (2007), Title, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract #####-##.