Including a melting layer in microwave radiative transfer simulation for clouds

A simple method is presented for the inclusion of melting layer microwave r adiative properties into cloud model simulations. These can be used for sen sitivity studies of passive and active microwave signatures of rainclouds a s well as for the generation of retrieval databases for aircraft and satell ite radar/radiometer applications. Tables of bulk cloud cell microwave radi ative parameters (extinction coefficient, single scattering albedo, asymmet ry parameter, radar reflectivity) are constructed and applicable to all hyd rometeor classes provided by current bulk models. The radiometric effect of simulated melting layers was compared to observat ions from the Tropical Rainfall Measuring Mission (TRMM), i.e.. the TRMM Mi crowave 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 f rom two numerical cloud models at various spatial resolutions. Considering the large variety of observed rain systems, a good agreement between observ ations and simulations concerning both brightness temperature distributions and brightness temperature offsets due to bright bands was identified at l ower frequencies. The melting layer model cannot compensate for insufficien cies of cloud model lee microphysics, so that significant differences betwe en simulations and observations at high microwave frequencies are noted. (C ) 2001 Elsevier Science B.V. All rights reserved.