Comparison of Rain Rates over the Ocean Derived from TRMM Microwave Imager and Precipitation Radar

Surface rain rates over the ocean derived from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and precipitation radar (PR) are compared and systematic differences between TMI-derived rain rates and PR-derived rain rates are shown. Three plausible reasons for these differences were found. One is a problem in the freezing-level assumption in the TMI algorithm for midlatitude regions in the winter, which results in underestimation of TMI-derived rain rates. Second is inadequate Z–R or k–R relationships for convective and stratiform types in the PR algorithm. Third is the incorrect interpretation of the rain layer when the freezing level is low and the rain type is convective. The strong brightband echo seems to be interpreted as rain and a too strong rain attenuation correction is applied. This results in a too strong rain rate by the PR algorithm.