COST-G: Status and new developments

In June 2025, the RL02.1 GRACE and GRACE-FO time-series of monthly gravity fields, combined from the monthly solutions of 11 (GRACE), resp. 8 (GRACE-FO) different Analysis Centers (ACs) by the Combination Service for Time-variable Gravity fields (COST-G) has been published. Compared to the COST-G RL02 combination, presented at EGU 2025, the contributions of HUST and Tongji to the GRACE combination have been updated, with only minor impact on the combination. Meanwhile, the Tongji GRACE-FO solutions have passed the COST-G quality control and are included in the operational GRACE-FO combination, starting from July 2025. One month later, a new AIUB GRACE-FO RL03 became available, replacing AIUB-RL02 in the GRACE-FO combination from August 2025 on. Both changes led to significant noise reductions of the combined GRACE-FO gravity fields. To ensure consistency of the atmosphere and ocean dealiasing (AOD) models applied in the GRACE-FO data analysis, the new time-series, which already use AOD1B-RL07, have to be transformed back to AOD1B-RL06 prior to combination. A new COST-G release, including a switch to AOD1B-RL07, is foreseen, as soon as the GRACE-FO SDS RL07 time-series are available. Due to the realistic noise models applied by an increasing number of ACs, a combination on the normal equation instead of solution level may become feasible for this future COST-G release.