Variational Retrievals Using SSM/I and SSM/T-2 Brightness Temperatures in Clear and Cloudy Situations

Abstract

Abstract The direct assimilation of brightness temperatures (Tb’s) from the Defense Meteorological Satellite Program Special Sensor Microwave Imager (SSM/I) and Special Sensor Microwave Water Vapor Profiler (SSM/T-2) in a one-dimensional variational (1D-Var) assimilation system is studied over the oceans. The control variables of the 1D-Var are the natural logarithm of specific humidity (lnq), near-surface wind speed (SWS), and cloud liquid water (CLW) path. Synthetic Tb’s, with and without noise added, were simulated and used to estimate the strength of the 1D-Var assimilation (weight given to the observations) and the information content of the Tb. In clear skies, it is shown that except for very dry profiles (TPW < 5–6 kg m−2) SSM/I Tb’s are superior to the SSM/T-2 Tb’s for the determination of total precipitable water (TPW). In the presence of clouds, the SSM/T-2 TPW retrievals are underestimated and the underestimation increases with CLW. Cloudy profiles should be filtered out. It is also shown that ...