Situation Dependent All-Sky Microwave Observation Error Adjustments in JEDI Skylab

Correct observation error specification is a crucial component of a well-functioning data assimilation system, especially when assimilating all-sky satellite microwave radiances. The observation error is much higher for observations in cloudy regions than in clear sky, typically due to mislocation errors. The observation error must therefore be adjusted depending on the scene. Current operational forecast systems, such as those at the ECMWF, use the mean of observed and modeled cloud amount, also called symmetric cloud amount, to make this adjustment. This technique has been proven to work well, however, current implementations are conservative in their error assignment strategy particularly for completely overcast scenes where the model and observation are in agreement. The current strategies use a maximum error for all regions that have a symmetric cloud amount greater than approximately 50-60%. This maximum for the mixed scenes is appropriate as partly cloudy regions are expected to have the largest mislocation error, however it may unnecessarily reduce the weight of the observations in fully overcast scenes, where the model and observations agree. The purpose of the current study is to test the impact of decreasing the observation error for satellite microwave radiances as it approaches fully overcast situations. The Joint Effort for Data Assimilation Integration (JEDI) data assimilation system interfacing with the Unified Forecast System (UFS) model will be used to test these adjustments on observations from various microwave sensors including the Advanced Microwave Sounding Unit-A (AMSU-A) and the Advanced Technology Microwave Sounder (ATMS).