Optimized J2 Recovery for Multi-Decadal Geophysical Studies

Abstract

The time history of the Earth's dynamic oblateness, or $J_2$, is a unique climate data record, with its estimation from satellite laser ranging (SLR) tracking data beginning in 1976. Due to its impact on variations in length of day (LOD), the long-term $J_2$ time series is frequently applied to LOD studies and their contributions, which include tidal friction, glacial isostatic adjustment, ice melt, sea level change, and the angular momentum exchange between the fluid outer core and the mantle. Previous studies demonstrated that the accurate recovery of $J_2$ requires the use of time variable gravity models from GRACE when processing the SLR tracking data. However, no reliable models exist prior to GRACE's 2002 launch, calling into to question the accuracy and utility of the pre-GRACE estimates. Here we present a new approach to accurately recover $J_2$ without gravity modeling, resulting in the first fully consistent long-term solution for climate studies.