Consolidated and validated monthly gravity field combinations of the GRACE, Swarm and GRACE-FO satellite missions

The satellite missions GRACE and GRACE-FO, dedicated to the observation of the time-variable Earth gravity field, provide invaluable insight into continental total water storage, continental ice mass change and ocean mass change at spatial scales of 200-400 km and monthly time-resolution, covering the time-period 2002 to present. The Combination Service for Time-Variable Gravity Fields (COST-G) of the International Association of Geodesy (IAG) collects the monthly gravity fields of its associated or partner Analysis Centers (ACs) and performs a weighted combination to provide a consolidated time-series of monthly gravity fields at Level-2 (spherical harmonic coefficients) and user-friendly Level-3 (post-processed global grids) products. Gaps in the GRACE or GRACE-FO time-series may be bridged by monthly gravity fields derived from orbits of the Swarm satellites, dedicated to the observation of the Earth magnetic field, at the cost of significantly reduced spatial resolution. COST-G performs quality control and harmonization of the contributing GRACE, GRACE-FO or Swarm time-series. The combined gravity fields undergo consistency checks and internal validation by the COST-G validation centers at GFZ and GRGS. An independent board of experts in hydrological, oceanic and cryosphere applications irregularly performs external validations. A combined re-processed GRACE time-series COST-G GRACE RL01 is available at the International Center for Global Earth Models ICGEM (L2-products) or the Gravity Information Service GRAVIS (L3-products), both operated by GFZ. The operational GRACE-FO time-series is updated regularly with a latency of less than 3 months, Swarm gravity fields are operationally combined in a quarterly processing scheme.