Geophysical contributions to satellite nodal residual variation

Even-degree zonal gravitational variations due to mass redistribution withi n the Earth's system, especially in the atmosphere, hydrosphere, and oceans will lead to variations in the nodal precession rate of satellite orbit. T he accurately measured nodal variation for LAGEOS 1 provides a means to stu dy planetary-scale mass redistributions and gravitational variations from t he space. In this paper, we investigate atmospheric and hydrologic contribu tions to the LAGEOS 1 nodal changes using barometric pressure, soil moistur e, and snow accumulation values from data-assimilating numerical models. Oc eanic effects are estimated from nonsteric sea level change determined by T OPEX/Poseidon satellite radar altimeter observation and a simple model for steric sea level changes. The results are compared with the LAGEOS 1 nodal change time series observed by satellite laser ranging. At annual and semia nnual time scales, the atmosphere and hydrosphere provide significant contr ibutions. The atmosphere provides broadband excitation of nodal changes at intraseasonal timescales. Seasonal and intraseasonal nontidal oceanic effec ts are also significant. General agreement between predicted and observed n odal precession rate residuals is improved relative to earlier studies, in part because of the better estimation of hydrological effects and new asses sment of nontidal oceanic effects.