Wednesday, 17 January 2007
Observations of three-body scattering signatures with a polarimetric and conventional WSR-88D radar
Exhibit Hall C (Henry B. Gonzalez Convention Center)
Three body scattering signatures (TBSS's) are reflectivity spikes radially orientated downrange from a storm region exhibiting high reflectivity. TBSS's are generally attributed to scattering in the Mie regime and thus indicate volumes dominated by large hydrometeors. In this study, examples of TBSS's are examined using both polarimetric and conventional radar data. The National Severe Storms Laboratory's polarimetric radar, KOUN, is used to study the effects of three-body scattering on differential reflectivity, differential phase shift, and cross correlation coefficient within a storm region exhibiting the rare signature. Radial plots of polarimetric variables, through the hail core and associated TBSS, are examined. Confirmed is the inverse cube (r-3) dependence of the echo power from the center of the hail volume to the corresponding reflecting ground ring. Conventional radar data from KFTG in Denver, CO is then considered. An unusual ‘fanning' of the TBSS was discovered as the large hail producing storm passed directly over the radome on 21 June 2001. A plot of echo power is made to determine if the ‘fan' was produced by a three-body scattering regime. Reflectivity, spectrum widths and radial velocities are then examined along radials exhibiting TBSS. TBSS's present a unique opportunity to forecasters to recognize storms that are producing large hydrometeors. Considering polarimetric upgrades are slated for all WSR-88D radars, an understanding of the polarimetric variables within TBSS's becomes valuable. Specific recognition of TBSS's using these alternative methods may prove useful in future operational automatic hail detection.