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Revealing layers of pristine oriented crystals embedded within deep ice clouds using differential reflectivity and the co-polar correlation coefficient

Keat, W. J. and Westbrook, C. D. (2017) Revealing layers of pristine oriented crystals embedded within deep ice clouds using differential reflectivity and the co-polar correlation coefficient. Journal of Geophysical Research: Atmospheres, 122 (21). pp. 11737-11759. ISSN 2169-8996

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To link to this item DOI: 10.1002/2017JD026754

Abstract/Summary

Pristine ice crystals typically have high aspect ratios (>>1), have a high density and tend to fall preferentially with their major axis aligned horizontally. Consequently, they can, in certain circumstances, be readily identified by measurements of differential reflectivity (ZDR), which is related to their average aspect ratio. However, because ZDR is reflectivity-weighted, its interpretation becomes ambiguous in the presence of even a few, larger aggregates or irregular polycrystals. An example of this is in mixed-phase regions that are embedded within deeper ice cloud. Currently, our understanding of the microphysical processes within these regions is hindered by a lack of good observations. In this paper, a novel technique is presented that removes this ambiguity using measurements from the 3 GHz Chilbolton Advanced Meteorological Radar in Southern England. By combining measurements of ZDR and the co-polar correlation coefficient (ρhv), we show that it is possible to retrieve both the relative contribution to the radar signal and “intrinsic” ZDR (ZPDRI) of the pristine oriented crystals, even in circumstances where their signal is being masked by the presence of aggregates. Results from two case studies indicate that enhancements in ZDR embedded within deep ice clouds are typically produced by pristine oriented crystals with ZPDRI values between 3 and 7 dB (equivalent to 5-9 dB at horizontal incidence) but with varying contributions to the radar reflectivity. Vertically pointing 35 GHz cloud radar Doppler spectra and in-situ particle images from the FAAM BAe-146 aircraft support the conceptual model used and are consistent with the retrieval interpretation

Item Type:Article
Refereed:Yes
Divisions:Faculty of Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
ID Code:73025
Publisher:American Geophysical Union

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