Including a melting layer in microwave radiative transfer simulation for clouds

A simple method is presented for the inclusion of melting layer microwave radiative properties into cloud model simulations. These can be used for sensitivity studies of passive and active microwave signatures of rainclouds as well as for the generation of retrieval databases for aircraft and satellite radar/radiometer applications. Tables of bulk cloud cell microwave radiative parameters (extinction coefficient, single scattering albedo, asymmetry parameter, radar reflectivity) are constructed and applicable to all hydrometeor classes provided by current bulk models. The radiometric effect of simulated melting layers was compared to observations from the Tropical Rainfall Measuring Mission (TRMM), i.e.. the TRMM Microwave Imager (TMI) and the Precipitation Radar (PR). A classification of rain systems into stratiform and stratiform with melting layer was carried out at the resolution of the TMI in order to isolate the average signature of melting particles. These were compared to three simulation experiments from two numerical cloud models at various spatial resolutions. Considering the large variety of observed rain systems, a good agreement between observations and simulations concerning both brightness temperature distributions and brightness temperature offsets due to bright bands was identified at lower frequencies. The melting layer model cannot compensate for insufficiencies of cloud model lee microphysics, so that significant differences between simulations and observations at high microwave frequencies are noted. (C) 2001 Elsevier Science B.V. All rights reserved.