Closed Loop Simulations Evaluating the Resolvability of Climate-Related Mass Transport Signal in Current and Next-Generation Satellite Gravity Missions

The existing observation record of satellite gravity missions spans more than two decades and is already closing in on the minimum time series of 30 years needed to decouple natural and anthropogenic forcing mechanisms according to the Global Climate Observing System (GCOS). Next Generation Gravity Missions (NGGMs) are expected to be launched within this decade, setting high anticipation for an enhanced monitoring capability that will improve the spatial and temporal resolutions of gravity observations significantly. They will allow an evaluation of long-term trends in the Terrestrial Water Storage (TWS) signal. The observations might therefore be used to verify climate projections and give additional inputs to the climate modelling community. This contribution shows numerical closed-loop simulation results of a GRACE-type in-line single-pair missions and Bender double-pair missions with realistic noise assumptions for the key payload and ocean-tide background model errors. The gravity signal in the simulations is based on modeled mass transport time series of components of the TWS, obtained from future climate projections until the year 2100 following the shared socio-economic pathway scenario 5-8.5 (SSP5-8.5). It evaluates different parameter models, among them the recoverability of long-term climate trends, annual amplitude, and phase of the TWS employing closed-loop numerical simulations of different current and NGGM concepts. Special emphasis shall be given on the robustness of the estimated TWS long-term-trend for different parameter models applied in different simulation scenarios, systematic changes, as well as on the methodology of the simulation themselves.