The use of mascons to resolve time-variable gravity from GRACE

We have analyzed intersatellite data from the GRACE mission (Gravity Recovery and Climate Experiment) to resolve time-variable gravity using a local mascon approach. The spherical harmonic solutions have resolved the signal from surface hydrology over land areas at spatial scales of 750 to 1000 km over one month intervals (Wahr et al., 2004; Tapley et al., 2004a). In our local approach, we solve explicitly for the mass of water in surface blocks using only the intersatellite data collected as the GRACE spacecraft overfly the region of interest. The local representation of gravity minimizes leakage of errors from other areas due to aliasing or mismodelling. We review solutions for mascons from July 2003 to August 2004 over three regions: the Amazon, the Indian subcontinent, and the continental United States. We solve for mass change at 10-day intervals using 4° × 4° blocks using a temporal and spatial constraint. The mascon solutions clearly resolve the annual signal over all three regions and show evidence of shorter period variations in parts of the continental U.S.