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Mixed-phase clouds involve complex processes. The characterization of these processes requires novel measurement techniques. One approach is to utilize polarimetric Doppler cloud radars, since their measured variables are sensitive to specific fall velocities and shapes of hydrometeors. Polarimetric retrievals for particle shape and orientation detection already exist, but provide so far only information about the main particle population.
In state-of-the art polarimetric approaches, elevation (range-height indicator, RHI) scans of observed differential reflectivity ZDR and correlation coefficient RHV of the main particle population are compared with modeled angular dependencies of differential reflectivity and correlation coefficient. The retrieval output is a pair of the polarizability ratio and the degree of orientation corresponding to the best agreement between measured and modeled angular dependences of the polarimetric variables.
It is aim of the herein study to extend an existing main-peak retrieval. Basis of the approach is, that the Doppler spectrum is split into five parts. The retrieval is then applied separately on each part. In the frame of this paper the application of the shape and orientation approach to RHI scans (30° to 90° elevation) of spectrally resolved polarimetric Ka-band cloud radar observations of ZDR and RHV for all 5 parts of Doppler spectra are demonstrated and results of observed spectrally resolved shape distributions will be presented. Case studies will be shown which demonstrate well that ZDR and RHV behave differently for the different parts of the Doppler spectra.
From our study we conclude that the extended approach enables one to track how ice particle shapes change during precipitation from cloud top to melting layer. By applying best-guess density estimates, the retrieved polarizability ratios will be converted to geometrical axis ratios. Interpretations of the pathway of such a hydrometeor evolution will be presented by considering in addition the presence of supercooled liquid droplets, which allows to distinguish between riming and aggregation processes.
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