Combination and analysis of the SLR monthly Earth’s oblateness variation solutions from different processing strategies

The publicly available SLR-derived monthly Earth’s oblateness C20 (or J2) time series exhibits varying levels of noise or systematic errors depending on the processing strategies used during estimation. We propose the use of two strategies, variance component estimate (VCE) and equal weighting (EW), to combine the SLR-derived J2 time series from four internationally renowned institutions. The resulting combined J2 time series is theoretically expected to demonstrate enhanced quality by reducing noise and systematic errors compared to individual contributions. These two combined solutions alongside four individual solutions are then discussed by analyzing their effects on global and local mass changes, thus exploring the potential for an optimized J2 time series in GRACE applications. The two combined SLR-derived J2 time series can assess the accuracy of the GRACE-derived J2 time series, which has shown poor but progressively improving accuracy. Results indicate that the RL06 version model of GRACE-derived J2 significantly outperforms the RL05 version, thus rendering the 160-day ocean tide effect in RL06 negligible. Moreover, significant discrepancies and lower quality among the various institutions' GRACE-derived J2 lead to Antarctic/Greenland ice sheet mass change estimates notably deviating from SLR-derived results. Therefore, upon replacing the GRACE-derived J2 time series with the VCE-combined SLR-J2 time series, the difference between the calculated mass change of the Antarctic/Greenland ice sheet and the RACMO2.3p2 model is theoretically the smallest, displaying the highest correlation coefficient between them.