Temporal Variation of the Geopotential : Processes and Interactions Among the Earth ’ s Subsystems

Seasonal variations in the Earth’s gravitational field arc investigated through the analysis of LAGEOS I satellite laser ranging measurements and are compared with those produced by atmospheric mass redistribution as inferred from global surface pressure data from the National Centers for Environmental Prediction (NCEP) reanalyses. The effect of oceanic tides and groundwater are considered as well. Focusing on the even zonal harmonics, atmospheric pressure fluctuations and ground water are shown to be the dominant cause of the observed zonal gravitational field variation at the annual period. At the semi-annual period, the modeled effect of the self-consistent equilibrium ocean tide dominates. The geographical distribution of the seasonal atmospheric variations are addressed. The potential use of I. AGEOS for studies of polar ice sheet variation and the need for good atmospheric pressure data in this region are stressed.