The detection of low-level vortices in convective storms using CASA dual-polarimetric x-band radar

The Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere (CASA) is funded by the National Science Foundation with the objective to create low-power, low-cost, short-range (X-band) radars that can be deployed on cell-phone towers. Multiple CASA radars are deployed collectively, together comprising an integrated network with radars operating collaboratively and adaptively, sensing when and where end-user needs are greatest. In 2006, a testbed called Integrated Project 1 (IP1) was placed in southwest Oklahoma. Each radar in the CASA network has a range of 40 km, a bandwidth of 1.8 degrees, dual-polarization capability, and rapid update capacity (~1 minute refresh).

On 2 April 2010, a quasi-linear convective system (QLCS) moved northeastward through central Oklahoma around sunrise with at least three distinct vortices embedded within this convective system in the CASA domain. Two of the three vortices caused damage in Rush Springs, Oklahoma, and were sampled in close range (<10 km) by the CASA radar near Rush Springs. The CASA radar provided high spatial and temporal resolution of these vortices not available through conventional NEXRAD. It was found through the CASA radar data: 1) the damage in Rush Springs was caused by both the fast translation speed and the embedded vortices; 2) differential reflectivity (ZDR) arcs were propagating and redeveloping along the QLCS as new vortices developed; 3) there was a minimum in the correlation coefficient at the center of the vortex (~0.1 km AGL), indicating the likely existence of a polarimetric tornado debris signature (TDS). The advantages and disadvantages of CASA radar compared to NEXRAD will also be discussed.