85th AMS Annual Meeting

Sunday, 9 January 2005
Estimating hail size using polarimetric radar
Angela K Rowe, Millersville University of Pennsylvania, Millersville, PA; and P. L. Heinselman and T. J. Schuur

This study investigates the use of polarimetric variables for estimating hail size. Archived data from the KOUN polarimetric radar in Norman, Oklahoma are obtained for three hail-producing events during 2004: 24 May, 29 May, and 2 June. A total of 45 hail reports are used for analysis, including hail sizes ranging from 0.75 to 4.25. Horizontal and vertical structures of reflectivity at horizontal polarization (ZH), differential reflectivity (ZDR), and correlation coefficient (rHV) associated with these reports are examined using Interactive Data Language (IDL) programs. Comparison of these images allow for the hail to be categorized into two groups based on ZDR and rHV signatures: hail less than 1.75 in diameter and hail 1.75 or higher in diameter. RHI images reveal differences in the vertical structures of these categories; extended columns of low ZDR and rHV are observed for the larger hail. Also, vertical profiles of these variables show a more significant decrease in rHV below the melting layer for hail 1.75 or larger. Box-and-whisker plots and discriminant analysis are then used to determine the ability of ZDR and rHV to distinguish between the two categories. Although ZDR appeared promising for estimating hail size, the discriminant analysis revealed that rHV is the best variable to discriminate between the categories.


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