Sub-monthly Terrestrial Water Storage Change from GRACE-C and NGGM: Assessing MAGIC’s Capability for Rapid Mass Change Monitoring

Abstract

By mitigating temporal aliasing errors caused by unresolved high-frequency atmospheric and oceanic mass variations, MAGIC is expected to provide substantially improved estimates of terrestrial water storage (TWS) changes. To date, MAGIC's performance has been evaluated primarily using global gravity field inversions. In this presentation, I evaluate its performance using the Line-of-sight Gravity Difference (LGD) approach, with a particular focus on addressing two major limitations of the current GRACE/-FO missions for terrestrial hydrology: their coarse spatial resolution of ~300 km and monthly temporal sampling, which limit their ability to monitor rapidly evolving events such as floods. To this end, I perform a regional inversion of sub-monthly (10-day) surface water storage changes over the Amazon Basin. The Amazon's large-amplitude, localized hydrologic signals and rapid sub-monthly variability provide an ideal test case for evaluating spatial resolutions finer than the ~300 km achievable with monthly GRACE/-FO solutions. The results show that, for 10-day TWS change solutions, GRACE-C and NGGM achieve comparable performance at a spatial scale of 330 km, whereas NGGM outperforms GRACE-C at 220 km and 165 km. NGGM recovers approximately 80% and 65% of the 10-day TWS signal at spatial scales of 220 km and 165 km, respectively, representing a 15-20% improvement over GRACE-C. I also quantify the effects of orbital geometry (i.e., the inclined orbit) and altitude on NGGM’s improved results. Between latitudes ±70°, the improved performance of MAGIC is largely driven by the contribution of the inclined NGGM pair. These results demonstrate the potential of MAGIC to substantially advance spatiotemporal monitoring of TWS change and enable observations of hydrologic processes at spatial and temporal scales beyond the capabilities of the current GRACE/-FO missions.