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September 16 - 20, 2002
DDC:
550 - Earth sciences
Abstract:
Antarctica is the coldest, stormiest and the most remote continent on Earth. Nearly 75% of the world's fresh water is trapped in the Antarctic ice sheets, which could significantly raise the global sea level if the ice sheets would melt. The continental ice sheet mass balance budget remains one of the largest uncertainties in the understanding of the causes of global sea level rise. Advanced gravity mapping satellite missions, such as CHAMP, GRACE and GOCE, are anticipated to provide significant measurements in the form of temporal gravity field to quantify ice sheet mass balance and its contribution to global sea level rise. To fully exploit of the accuracy of GRACE, equivalent of less than several mm-level measurement accuracy of ground water movement over a spatial scale of 200 km monthly at satellite altitude, the knowledge of the surface pressure fields over Antarctica is needed at an accuracy of sub-mbar (rms). The current operational meteorological analyses from ECMWF (6-hourly), and NCEP (3-hourly), both with 100 km spatial resolutions, are inadequate both in accuracy and resolution for an adequate correction of the GRACE measurements to extract ice sheet mass balance signals. In this paper, we study the use of spaceborne GPS occultation measurements from CHAMP, SAC-C and GRACE to potentially provide an improved atmospheric pressure field for GRACE gravity corrections. The retrieved atmospheric measurements are studied based on assumption that water vapor is scarce over the interior of the Antarctic continent, to compute pressure profiles. Improved pressure fields could also be available by employing 4DVAR assimilation techniques using bending angles and refractivities derived from GPS occultations. In this paper, results will be presented in comparing operational meteorological analysis models (NCEP and ECMWF) as well as their validation using Automatic Weather Stations (AWS) data in Antarctica. It is also demonstrated that GPS occultation technique could be a substantially valuable data source to enhance the model prediction and analysis. Potential improvements of the pressure field over southern ocean and Antarctica using GPS occultation technique is discussed at the end.
