Retrieval of the microphysical properties of mixed-phase clouds using doppler polarimetric tools

Conference paper (2009)

Authors

Y. Dufournet International Research Centre for Telecommunication and Radar
C.M.H. Unal Microwave Technology and Systems for Radar
HWJ Russchenberg Microwave Technology and Systems for Radar
Research Group
International Research Centre for Telecommunication and Radar
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Published Date

2009

Language

Undefined/Unknown

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Research Group

International Research Centre for Telecommunication and Radar

Abstract

Nowadays, it is still not really clear how the large panel of different cloud microphysical characteristics influences the radiative balance at a global scale. This leads to great uncertainties in assessing the cloud radiative forcing effect. Observations strategies are therefore developed to better determine and understand the worldwide relative proportion of clouds, in term of phase, particle habits, particle size distribution and orientation.
The focus of this work lies on the observation, at high resolution, of ice crystals within mixed-phase clouds using the S-Band atmospheric radar TARA. Combining the Doppler and polarimetric capabilities of such radar, spectral parameters as the spectral differential reflectivity sZDR can be measured. First, from this parameter only, ice particle orientation and the degree of sphericity of the crystals are derived for each time and range bins. In a second step, the measured Doppler spectrum is compared and fitted with a simulated one obtained from a microphysical model based on spheroidal particle shapes. The ice particle size distribution, and consequently the ice water content, for different crystal habits can then be retrieved assuming that sZDR gives the axial ratio (from dual polarization) versus the size (from Doppler velocities) of the ice crystals.
A great care is taken to obtain reliable spectral parameters. It will be discussed in this paper. Then results of the retrieval technique will be illustrated using collocated ground-based and aircraft measurements taken during the COPS campaign (Convective and Orographically-Induced Precipitation Study) in the black forest, Germany, in 2007.