A Self-Consistent Numerical Method for Microphysical Retrieval in Rain Using GPM Dual-Wavelength Radar

An assessment of the performance of a self-consistent numerical method for dual-frequency radar based on the retrieval of microphysical precipitation parameter profiles is presented. From the surface reference technique (SRT), the estimation of path-integrated attenuation (PIA) is performed at both wavelengths and reflectivity factors are corrected for attenuation. Then, solving numerically a system of two nonlinear differential equations, the drop size distribution (DSD) parameters are obtained. The method is applied only in the stratiform rain region, from the surface along the path upward to the brightband bottom. Assuming a gamma DSD model to describe the distribution of precipitation found in nature, a methodology has been developed to transform the estimated DSD provided by a vertically pointing Micro Rain Radar to a profile given by a ground-based Ku- and Ka-band radar, and then in a spaceborne dual-frequency radar measurement profile. Under ideal conditions in which the different errors that simultaneously affect the retrieval of precipitation microphysical parameters may be individually studied, particular emphasis has been placed on the incidence of variability due to the DSD shape parameter μ , the presence of uncertainties in PIA estimates, and radar signal fluctuations. To achieve an appropriate level of confidence in the simulation outputs, a qualitative indirect method of validation was realized by comparing the results obtained by the simulation with the experimental ones and weighing how consistent they are with what the theory implies. GPM near-real-time data from an entire year (October 2014–September 2015) were used for this purpose.