Secular variations of the zonal gravity field, global sea level and polar motion as geophysical constraints

Abstract

Satellite Laser Ranging (SLR) data have been analyzed by ourselves and other groups to provide estimates of the secular variations in the zonal harmonics of the geopotential field. While the SLR data available from late-1992 onward are superior in satellite and temporal coverage (two station shifts in operation by the NASA Network), SLR data extending back to the mid-1970s have been utilized by some of the analysis centers. Two solutions for secular zonals and the SPACE'93 secular polar motion rates are evaluated to provide constraints on geophysical models describing post-glacial rebound (PGR) and ice sheet mass balance/sea level rise using an inverse method. The observed secular rate of global sea level change is also used as a constraint in various solutions. The benefits of forward modeling the water impoundment in reservoirs and the contributions of the mountain glaciers to the observed secular terms are discussed. Although the number of well resolved time dependent geopotential terms is limited, the inverse solutions are promising and provide results consistent with IPCC estimates of ice sheet mass balance and optimal estimates of mantle viscosity contrasts.