1A.6 Retrieving the Microphysics of Mixed - Phase Regions Embedded within Deep Ice Clouds using Dual Polarisation Radar

Monday, 14 September 2015: 11:45 AM
University AB (Embassy Suites Hotel and Conference Center )
W. J Keat, Reading, United Kingdom; and C. Westbrook and A. J. Illingworth

Mixed-phase clouds are fundamental to the production of precipitation, and play an important role in Earth's radiation budget. Yet our understanding of the spatial and temporal extent of these conditions remains poorly understood, primarily due to a lack of suitable observations. In the presence of supercooled liquid water, pristine oriented crystals grow rapidly by the Bergeron-Findeison mechanism. Since pristine oriented crystals preferentially fall with their major axis horizontally aligned, these crystals can sometimes be observable using dual polarisation radar as regions of elevated differential reflectivity (ZDR). However, observing their signal when they exist amongst larger aggregates is challenging because the aggregates mask the signal from the pristine crystals. We present a new method to identify and retrieve the microphysics of these mixed-phase regions embedded within deep ice clouds using observations from the Chilbolton Advanced Meteorological Radar. We use the co-polar correlation coefficient (ρhv) which characterises the mixture of particle shapes in a sample volume to reveal the presence of pristine crystals, even when they are masked by larger aggregates in the ZDR field. By combining observations of ρhv and ZDR with a two-population forward model, the fraction of radar reflectivity from the pristine crystals and aggregates and the intrinsic differential reflectivity (ZDRI) of the pristine crystals can be retrieved. Preliminary retrieval results for ZDRI are consistent with laboratory experiments of pristine crystal growth, and allow us to assess the contribution of the pristine crystals to the overall precipitation rate.
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