Resolving Climate-related Mass Transport Trends—a Parameter Model Comparison using Closed-loop Simulations of Current and Future Satellite Gravity Missions

The existing observation record of satellite gravity missions 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). The next generation of gravity field missions (GRACE-C, NGGM) are expected to be launched within this decade. These missions as well as their combination (MAGIC) are setting high anticipation for an enhanced monitoring capability that will improve the spatial and temporal resolution of gravity observations significantly. This study investigates and compares the performance of three different trend estimation strategies for the first time in multi-decadal numerical closed-loop simulations of satellite gravimetry constellations. The parameter models used in this study consist of monthly solutions (\(\:{f}_{0}\)), co-estimation of monthly and trend parameters (\(\:{f}_{1}\)), and the direct estimation of trend and annual amplitudes (\(\:{f}_{2}\)). The considered satellite constellations are a GRACE-type in-line single pair mission and a MAGIC double pair mission with realistic noise assumptions for the key payload, tidal and non-tidal background model errors. The gravity signal in the simulations is based on 30 years of modeled mass transport time series of components of the terrestrial water storage, obtained from future climate projections. Our results show the potential of MAGIC’s advanced observation system in estimating a long-term trend. After 10 years, the global rms of the trend estimates for the \(\:{f}_{0}\) parameter model improves from a single pair performance of 59.6 mm/yr to 1.2 mm/yr for MAGIC. Since all three parameter models show globally comparable results, further regional analysis is conducted dividing the world into 206 hydrological basins. Small basins and areas with low signal-to-noise ratio show small improvements in the residuals (e.g. 1mm/yr improvements in the residuals for single pair (\(\:{f}_{2}\)) compared to \(\:{f}_{0}\) after 10 years of observations). Furthermore, the regional analysis shows, that a significant number of basins show a higher signal-to-noise ratio compared to the global average. These basins would benefit from trend estimates of higher degree and order, which is possible by directly estimating the trend coefficients with \(\:{f}_{1}\) or \(\:{f}_{2}\), but not with the trend estimation from monthly solutions (\(\:{f}_{0}\)).