Time-variable gravity measurements from GRACE and GRACE-FO for hydrology and climate applications

The Gravity Recovery and Climate Experiment (GRACE) mission has been providing measurements of month-to-month variations of Earth's gravity field since 2002. Now in its 10th year in orbit, GRACE's intersatellite microwave ranging system continues to deliver high-quality data from which mass changes on or near Earth's surface can be inferred. These observations of mass changes have greatly advanced our understanding of how glaciers and ice sheets respond to climate change, the mass-addition component of global sea level rise is, and, perhaps most importantly for application purposes, revealed ongoing changes in terrestrial hydrology related to groundwater changes and drought impacts. GRACE measures mass changes independent of form (i.e., snow, ice, liquid water), and it is the only observation that can provide constraints on total mass changes over a region and therefore on the closure of regional and global water budgets. GRACE observations of groundwater withdrawal compare well with the sparse in-situ data over aquifers in the United States, and have led to improvements in hydrology models through data assimilation or parameter tuning. Similarly, ocean and land ice groups are now exploring the impact of assimilating the GRACE climate data record into their modeling systems. We will discuss the status of the current GRACE satellite system, examples and impacts of successful quasi-operational applications of GRACE data (e.g., for the National Drought Monitor), an overview of the development status and mission specs of the GRACE Follow On mission scheduled to launch in 2017, and general aspects of transitioning time-variable gravity observations from research to operations.