Analysis of the wind field in tornadic supercells using variational tracking of rapid-scan, polarimetric, mobile, Doppler radar data

Rapid-scan Doppler radars have adequate temporal resolution to document the evolution of tornadoes in supercells, which occurs on time scales ~ 1 – 10 s. Using data collected by the RaXPol (Rapid-scan, X-band, Polarimetric) mobile radar in a tornadic supercell on 24 May 2011 near El Reno, OK at 2-s intervals, two-dimensional analyses of the wind field were produced using a variational scheme for tracking reflectivity. Analyses were produced using various time intervals and compared. For a spatial resolution determined by the beamwidth of the antenna, antenna rotation rate (producing beam smearing if there is no electronic backscanning), range from the radar, and pulse length, the time difference associated with the “best” analyses must lie within a certain time window, neither too short nor too long. The tracking scheme is used to estimate the component of the wind normal to the beam, while the Doppler, radial wind component is used to resolve the component of the wind along the beam. When the horizontal gradient in reflectivity is close to zero, as in the debris region, tracking may not not be possible, but polarimetric variables such as the co-polar cross correlation coefficient or differential reflectivity, which may be less uniform in tornado debris clouds, or combinations of the variables, may make tracking possible. Experiments using the tracking of the polarimetric variables to augment the analyses based on the tracking of radar reflectivity are detailed. The effects of attempts to correct for attenuation, on the results, will also be described.