Simulation and sensitivity analysis for cloud and precipitation measurements via spaceborne millimeter-wave radar

This study presents a simulation framework for cloud andprecipitation measurements via spaceborne millimeter-wave radar composed ofeight submodules. To demonstrate the influence of the assumed physicalparameters and to improve the microphysical modeling of the hydrometeors, wefirst conducted a sensitivity analysis. The results indicated that the radar reflectivity was highly sensitive to the particle size distribution (PSD) parameter of the median volume diameter and particle density parameter, which can cause reflectivity variations of several to more than 10 dB. The variation in the prefactor of the mass-power relations that related to the riming degree may result in an uncertainty of approximately 30 %-45 %. Theparticle shape and orientation also had a significant impact on the radarreflectivity. The spherical assumption may result in an averageoverestimation of the reflectivity by approximately 4 %-14 %, dependent onthe particle type, shape, and orientation. Typical weather cases weresimulated using improved physical modeling, accounting for the particleshapes, typical PSD parameters corresponding to the cloud precipitationtypes, mass-power relations for snow and graupel, and melting modeling. Wepresent and validate the simulation results for a cold-front stratiformcloud and a deep convective process with observations from a W-band cloudprofiling radar (CPR) on the CloudSat satellite. The simulated bright bandfeatures, echo structure, and intensity showed a good agreement with theCloudSat observations; the average relative error of radar reflectivity inthe vertical profile was within 20 %. Our results quantify theuncertainty in the millimeter-wave radar echo simulation that may be causedby the physical model parameters and provide a scientific basis for optimalforward modeling. They also provide suggestions for prior physical parameter constraints for the retrieval of the microphysical properties of clouds and precipitation.