Comparisons between S‐, C‐ and X‐band polarimetric radar observations and convective‐scale simulations of the HyMeX first special observing period

This article describes a forward observation operator for polarimetric radar variables, developed within the research mesoscale non-hydrostatic model Meso-NH. The forward operator enables direct comparisons of atmospheric simulations with polarimetric radar observations and constitutes a first step towards the assimilation of polarimetric radar data. The parameters of the polarimetric forward operator were defined in order to be consistent (whenever possible) with the model microphysical parametrization. Subjective and quantitative comparisons between observations and simulations are analyzed for S-, C- and X-band radars for two convective cases that were observed in autumn 2012 in southeastern France during the first observing period (SOP1) of the Hydrological cycle in the Mediterranean Experiment (HyMeX) campaign. The good consistency between the medians of the observed and simulated distributions of Zdr and Kdp as a function of Zhh, in rain and in dry snow, enables the validation of the parametrization of the polarimetric forward operator. However, the higher spread in observed Zdr and Kdp (due to noise and microphysical variability) reveals a need for careful data quality control and pre-processing for use in assimilation. Comparisons between observed and simulated vertical profiles of Zhh, Kdp and Zdr in convective areas also show generally good agreement. Some differences between observations and simulations are attributed to model limitations, in particular its one-moment microphysics scheme and coarser resolution.