Assimilation of Spaceborne Radar Observations in the Goddard Earth Observing System (GEOS) Model

Abstract. Spaceborne radar observations provide valuable information on the vertical structure of precipitation and hydrometeors, making them an important resource for numerical weather prediction and model evaluation. The Joint Effort for Data assimilation Integration (JEDI) is the unified and configurable data assimilation system developed and stewarded by the Joint Center for Satellite Data Assimilation (JCSDA) on behalf of its U.S. federal partners being adopted in NASA’s Goddard Earth Observing System (GEOS) suite of products. This study describes a new spaceborne radar data assimilation capability developed for use in JEDI, including both the radar forward operator and the associated data assimilation components. This new capability is then demonstrated using observations from the Global Precipitation Measurement (GPM) Dual-frequency Precipitation Radar (DPR). The radar forward operator simulates reflectivities that agree well with observations, with mean differences typically below 2 dB during the August 2023–January 2024 test period. Consequently, a large number of DPR observations can be successfully assimilated into GEOS. Case studies of tropical cyclones show that DPR assimilation can substantially improve the analyzed distribution of precipitation and hydrometeors and, in some cases, improve atmospheric state variables such as wind, pressure, temperature, and water vapor. These results demonstrate the potential of spaceborne radar observations to improve the representation of precipitating systems in GEOS and, ultimately, the quality of future reanalyses and weather forecasts.