HR: 0800h
AN: G31C-0801    [Abstracts]
TI: Secular variations in the low degree zonal harmonics from 28 years of SLR data
AU: * Cheng, M
EM: cheng@csr.utexas.edu
AF: Center for Space Research, UT at Austin, 3925 W. Braker Ln #200, Austin, TX 78759 United States
AU: Tapley, B D
EM: tapley@csr.utexas.edu
AF: Center for Space Research, UT at Austin, 3925 W. Braker Ln #200, Austin, TX 78759 United States
AB: The secular changes in the Earth's gravity field are the consequence of long-term mass redistribution within the Earth system. The major components of these phenomena are due to the readjustment of the Earth to glaciation, including post-glacial rebound and the mass balance of the polar ice sheets and subpolar glaciers. Satellite Laser Ranging (SLR) data have recorded the global nature of these gravity variations, through their effect on the orbits of geodetic satellites, for almost three decades. A solution for the secular variations in the zonal harmonics up to degree 7 were determined from the SLR data from 8 geodetic satellites over the time period spanning 28 years from 1976 to 2003. This solution is consistent with the result within the range of uncertainty determined using data from 1976 to 1995 by Cheng, Shum and Tapley [1997]. Analysis of the monthly estimates of the second degree zonal (J2) indicates that, in addition to the secular drift, the 18.6 year tide and the seasonal variations, J2 has significant interannual variations with time scales of 4-6 years and ~21 years. These longer period variations significantly affect the estimate of the secular drift, with the most recent SLR data affecting the estimate much more than the earlier data. Such effects are less significant for the higher degree (> 2) zonal rates. In addition, comparison of the monthly solution of lower degree and order geopotential coefficients shows a good agreement except for J2 derived from recent SLR and GRACE data. Detailed comparisons and analysis will be presented.
DE: 1214 Geopotential theory and determination
DE: 1223 Ocean/Earth/atmosphere interactions (3339)
DE: 1241 Satellite orbits
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting