Impact of cycled 3DVAR assimilation of COSMIC observations on nor'easter simulations

Since their launch in 2006, satellites from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission have provided radio occultation (RO) measurements of tropospheric temperature and water vapor, among other products. The potential of COSMIC RO data assimilation to nor'easter simulations stems from COSMIC's global coverage, high frequency of observations (~1,800 per day), and well-resolved profiles (~60 m) of derived temperature and specific humidity. In this study, the impact on WRF-ARW version 3.2 simulations of nor'easters to three-hourly-cycled, three-dimensional variational data assimilation of COSMIC RO data is assessed. In particular, we compare WRF model output from seven nor'easter cases that occurred during the cold seasons of 2006–2010 with and without COSMIC RO data and compare each to corresponding GFS analyses and Stage IV precipitation data, which we consider representative of the observations. Preliminary results indicate a general improvement in both the sea-level pressure and 500-hPa geopotential height fields in six out of seven nor'easter simulations when COSMIC RO data was assimilated, despite the fact that the WRF model assimilates these data via its variational data assimilation program (WRF-Var) as if they were radiosonde observations.