Refinement Of Grace Gravity Model Including Earth'S Mean Mass Variations

The Gravity Recovery and Climate Experiment (GRACE) has observed the Earth's mass redistribution mainly caused by the variations of groundwater, ice sheet, and sea level since its launch in April 2002. The global gravity model estimated by the GRACE observation is corrected by barometric pressure, and thus represents the change of Earth mass on the Earth's surface and below Earth's surface excluding air mass. However, the total air mass varies due to the water exchange between the Earth's surface and the atmosphere. As a result, the nominal GRACE gravity model should include the Earth's gravity spectrum associated with the total air mass variations, degree 0 and order 0 coefficients of spherical harmonics (C-00). Because the water vapor content varies mainly on a seasonal time scale, a change of C-00 (delta C-00) is particularly important to seasonal variations of sea level, and mass balance between northern and southern hemisphere. This result implies that delta C-00 coefficients should be accounted for the examination of continental scale mass change possibly associated with the climate variations.