The Microphysics of the 14 June 2011 Norman, Oklahoma Downburst from Dual-polarization and Dual-Doppler Radar Measurements

Microphysics has important impact on the formation of downbursts that often affect aviation. On 14 June 2011, thunderstorms developed along a cold front in central Oklahoma in an unstable environment (CAPE > 3500 J kg^-1). One of the thunderstorms produced a wet downburst in Norman, Oklahoma that resulted in winds in excess of 30 m s^-1 and hail in excess of 4 cm in diameter at the surface. Extreme rainfall rates were also associated with this downburst; around 25 mm of rain was measured by the Norman Mesonet within 15 to 20 minutes. As a result, significant power outages and damage occurred in the northern parts of the city.

In this study, both experimental KOUN and operational KTLX WSR-88Ds were scanning this downburst at close range (<40 km). KOUN provided polarimetric radar data (PRD) while both radars provided some dual-Doppler coverage. Data were also collected by a 2D-video disdrometer during the later stages of the convective event at Kessler Farm Field Laboratory located about 28 km southwest of Norman. PRD from KOUN are analyzed to gain an understanding of the microphysics associated with the downburst. Drop size distribution (DSD) retrieval was conducted on the radar data to find parameters based on constrained-gamma (C-G) model. Through the DSD retrieval, statistics such as median diameter and rainfall rate were estimated to further quantify the data. These results are compared with dual-Doppler wind analysis from KOUN and KTLX and the 2D-video disdrometer data to reveal the relationship between cloud/precipitation microphysics and storm dynamics.