Introduction of a melting layer model to a rain retrieval algorithm for microwave radiometers

Abstract

Rain retrieval algorithm for spaceborne passive microwave radiometer with melting layer models is examined in this study. Two melting layer models proposed to explain the reflectivity profile of a bright band or radio wave attenuation observations are tested for the implementation into the rain retrieval algorithm by Aonashi and Liu(1). The attenuation property of a melting layer is examined by the path integrated attenuation obtained by measuring the surface echo of TRMM/PR data in low bright band height cases (e.g. < 2000m) and it is compared with model results because the PIA is closely related to the emission from the rain drops. Similarly, the relationship between the rain rates (R) derived from TRMM/PR and the brightness temperature (TB) derived from TRMM/TMI data for fixed brightband height is compared with the TB-R relationships from rain models with and without the melting layer model using the radiative transfer model by Liu(2). The results show that the effect of the melting layer is not negligible for passive microwave rain retrievals especially in weak rain rate cases and the retrieval error exceeds 20% for the rain rate less than 10 mm/h if the melting layer model is not introduced. The validity of the effect of the melting layer model in the retrieval algorithm is examined by using TRMM/PR data.