DOMUS: DOppler MUltiple-Scattering Simulator

Multiple scattering (MS) strongly affects CloudSat's W-band cloud-profiling radar (CPR) reflectivity when the satellite is overpassing moderate and heavy precipitation systems. With the upcoming deployment of W-band Doppler radars in space-Earth Clouds, Aerosols, and Radiation Explorer's CPR in primis-and the goal of retrieving vertical motions within convective systems, there is an urgent need to assess the impact of MS onto the Doppler signatures. A Monte Carlo code capable of simulating the reflectivity enhancement due to higher orders of scattering has been extended to include the Doppler effects. This paper presents the main guidelines for the inclusion of the Doppler analysis into the Monte Carlo scheme. To our knowledge, this simulator is the first one capable of simulating realistic Doppler signals in the presence of MS. The case studies are first presented in uniform beam-filling conditions for the profiles extracted from a cloud-resolving model simulation of deep convection (i.e., 1-D profiles are used to characterize a stratified atmosphere). The simulations demonstrate that, at ranges where MS contributions affect the overall radar signal, two main features appear as the following: 1) The Doppler spectrum tends to broaden with increasing MS enhancement, adding up to the single-scattering (SS) Doppler fading due to the satellite motion; and 2) the mean Doppler of the backscattered signal departs from the mean Doppler determined by the combined effect of the vertical-wind and hydrometeor-terminal velocities at all range bins below the altitude where the MS contribution significantly overcomes the SS. The simulator can be run in nonuniform-beam-filling conditions as well (i.e., a 3-D field is used to characterize the atmosphere at scales smaller than the radar resolution). With its cutting-edge capabilities, it provides a unique tool for the evaluation of the performances of the upcoming high-frequency spaceborne Doppler radars.