The detection of low-level misovortices embedded within a quasi-linear thunderstorm complex on 2 April 2010 by CASA 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. A demonstration testbed of four CASA radars was deployed in Oklahoma in 2006, and since that time has operated each spring and fall during convective events. 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 thunderstorm complex associated with a cold front moved northeastward through the CASA network around sunrise. The atmospheric conditions were characterized by very high low-level shear with 0-1 km helicity of over 300 m^2 s^-2. A couple of areas of rotation embedded within the complex were sampled in close range (< 10 km) by the CASA radar near Rush Springs. One circulation caused substantial damage in Rush Springs; winds were estimated at around 100 mph. The damage path was unique because all storm damage was on the south side of the circulation due to the fast storm motion to the northeast. This circulation came within several km of the radar, so very low-level radar observations were obtained. The magnitudes of these short-lived circulations (~10 min) were not easily detectable by the current NEXRAD system. This study will analyze both Doppler and dual-polarimetric attributes of these embedded circulations using data from the CASA and NEXRAD networks. In particular, the classification of the circulations will be discussed. These were not officially classified as tornadoes by The National Weather Service, but still caused equivalent to EF-1 damage in some locations. While previous studies on vortices within linear storm structures have been conducted (Carbone 1982; Weisman and Trapp 2003), cases like this show the continued challenges for the detection and warning of small-scale vortices.