In the focus of COST-G in the last two years has been its extension to become a truly worldwide Combination Service for Time-variable Gravity fields. With the inclusion of monthly solutions from Chinese Analysis Centers (ACs) in the operational GRACE-FO combination and the release of a consistently re-combined COST-G GRACE RL02 including, in addition to RL01, the contributions of four Chinese ACs and the LUH-GRACE2020 time-series, as well as updates of the AIUB and GRGS contributions, this goal has been achieved to the full extent. A positive impact of the enlarged basis of ACs on the quality of the combination is visible mainly during periods with increased noise due to orbit repeat patterns, data problems at the end of the GRACE mission, or high solar activity. Meanwhile, with the GRACE-C and NGGM satellite gravimetry missions, new challenges are on the horizon. With its experience in the combination of solutions or normal equations from numerous ACs applying diverse analysis tools and strategies, and with the planned extension to the combination of Satellite Laser Ranging (SLR) gravity field solutions, COST-G is in an excellent position to contribute to the MAGIC combination of GRACE-C, NGGM and SLR.
Meyer et al. (Wed,) studied this question.