34th Conference on Radar Meteorology


The ARMOR C-band radar polarimetric radar signatures of large hail: The April 10th 2009 severe weather outbreak over northern Alabama

Matthew E. Anderson, University of Alabama, Huntsville, AL; and L. D. Carey, W. A. Petersen, and K. R. Knupp

On April 10th 2009, a severe weather event of rare occurrence moved across the Tennessee Valley. The Storm Prediction Center (SPC) issued a moderate risk of severe storms for northeastern Alabama area early in the morning and as conditions worsened later in the day, the area was updated to the high risk category. A line of supercells formed across northeast Mississippi and northwest Alabama and moved eastward across the region producing numerous reports of large hail and an EF-3 tornado in Jackson and Dekalb counties in northeast Alabama. The storms occurred in the early afternoon with many people on the road and resulting in large amounts of damage to automobile and homes. The event was well sampled by the UAH ARMOR dual-polarimetric C-band radar located at the Huntsville International Airport. The ARMOR observed variables used for this study include Zh (radar reflectivity), Zdr (differential reflectivity), Kdp(specific differential phase), and ρhv (correlation coefficient). The SPC storm reports along with hail survey data will be used as ground truth for the study. The storm reports and the survey indicate that hail was reported across the area with a variety of shapes (e. g. spherical, oblate, and disc) and sizes ranging from small (pea size) to large (baseball size) hail. Participants in the survey noted that the hail had visible lumps, lobes, and growth rings, suggesting both wet and dry growth. The focus of this study is to evaluate traditional polarimetric radar methods for hail identification and size estimation (e. g. small vs. large), mostly developed at S-band, at C-band in a high impact weather event in the southeastern United States. With C-band radar, more hydrometeors tend to fall into the resonant scattering regime. Therefore, because of the different forms of scattering the polarimetric variables could be expected to differ in large rain drops, rain hail mixtures, and hail. Preliminary data analysis suggests that there are some similarities in the hail signatures such as a lowering in Zdr and phv in regions of large Zh. These and other polarimetric radar signatures will be compared against ground truth data with the ultimate goal of improving the robustness and accuracy of hydrometeor identification and hail size estimation at C-band.

extended abstract  Extended Abstract (352K)

Poster Session 13, Polarimetric Radar Applications and Techniques
Thursday, 8 October 2009, 1:30 PM-3:30 PM, President's Ballroom

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