The Possible Role of Descending Reflectivity Cores During the Intensification of the ‘El Reno Tornado' of 31 May 2013 Observed with a Rapid-Scan, Mobile, Doppler Radar

On 31 May 2013, the mobile, Rapid-scan, X-band, Polarimetric (RaXPol) Doppler radar collected a high spatiotemporal resolution dataset documenting the genesis, intensification, and dissipation of a tornado that caused EF-3 damage near El Reno, OK. RaXPol was deployed three times during the tornadic phase of this storm, between 4.5-11 km from the center of the tornado, and collected 360 degree PPI scans every 2 seconds with range gate spacing between 15 to 45 meters. Shortly after tornadogenesis, multiple descending reflectivity cores were identified through reconstructed vertical cross sections and three-dimensional renderings of the collected radar volumes. In at least two cases, strong surges within the rear-flank downdraft were observed and seemed to be associated with a descending reflectivity core making contact with the Earth’s surface. The associated convergence caused by these surges in momentum within the rear-flank downdraft appeared to affect the structure of the tornado on time scales of less than 30 seconds, often causing rapid intensification of the azimuthal velocities of the tornado and significant changes in the vertical structure of the tornadic vortex.