Determination of the vertical distribution of in-cloud particle shape using SLDR mode 35-GHz scanning cloud radar

Abstract

Abstract. In this study we present an approach that uses polarimetric variables from a scanning polarimetric cloud radar MIRA-35 in the 45° slanted linear depolarization (SLDR) configuration, to derive the vertical distribution of particle shape (VDPS) between top and base of mixed-phase cloud systems. The polarimetric parameter SLDR was selected for this study due to its strong sensitivity to shape and low sensitivity to the wobbling effect of particles at different antenna elevation angles. For the VDPS method, elevation scans from 90° to 30° elevation angle were deployed to estimate the vertical profile of the particle shape by means of the polarizability ratio, which is a measure of the density-weighted axis ratio. Results were obtained by retrieving the best fit between observed SLDR-vs-elevation dependencies and respective values simulated with a spheroid scattering model. The applicability of the new method is demonstrated by means of three case studies of isometric, columnar and oblate hydrometeor shapes, respectively, which were obtained from measurements at the Mediterranean site of Limassol, Cyprus. The identified hydrometeor shapes are demonstrated to fit well to the cloud and thermodynamic conditions which prevailed at the times of observations. Some observations reveal that in mixed-phased clouds ice particle shapes tend to evolve from a pristine columnar or dendritic state at cloud top toward a more isometric shape at cloud base. Either aggregation or riming processes contribute to this vertical change of microphysical properties. The new height-resolved identification of hydrometeor shape and the potential of the VDPS method to derive its vertical distribution are helpful tools to understand complex processes such as riming or aggregation, which occur particularly in mixed-phase clouds.