High-Resolution X-band Volumetric Observations of Spring 2015 Tornadoes with the Atmospheric Imaging Radar

The Atmospheric Imaging Radar (AIR) is a mobile X-band imaging weather radar system designed and built by the Advanced Radar Research Center (ARRC) at the University of Oklahoma. By transmitting a vertical, 20-degree fan beam and using a 36-element receive array, digital beamforming is used to form pulse-by-pulse RHIs with a native beamwidth of 1 degree by 1 degree. Rotation in the azimuthal dimension allows for sector scans up to 180 degrees, resulting in full 20x180 degree volumetric updates in as little as 10 seconds and 20x90 degree updates in under 6 seconds. By utilizing pulse compression, range resolution of 30 meters and acceptable sensitivity for meteorological observations are achieved. The combination of spatial and temporal resolution allows for the observation and analysis of tornado structure and evolution on extremely short timescales. During the spring of 2015, the AIR collected data on four supercellular tornadoes, including two "major" tornadoes at close range. Preliminary analysis of these two tornadoes, the 16 May 2015 Tipton, OK tornado and the 27 May 2015 Canadian, TX tornado are presented in this paper, with volumetric update rates of 6 and 5.5 seconds, respectively. The Tipton case includes a long-duration tornadic deployment, with over 30 minutes of continuous data at ranges as close as 11 km. Highly detailed animations are presented, showing subtle track shifts, rear flank gust front surges, and a “cigar signature” previously unreported in the literature. The Canadian case includes six minutes of volumetric tornadic dissipation data (from “wedge” to “rope” to full dissipation) at ranges as close as 4 km, resulting in tornado-scale observations of the condensation funnel in 3 dimensions. Volumetric vorticity analysis during the dissipation stages is presented in the form of animated loops showing the 3-dimensional rope out stage of the tornado with exceptional vertical resolution, representing the truly unique observational capabilities of the AIR.