Doppler Radar Wind Spectra of Supercell Tornadoes

Abstract

A storm-intercept team from the University of Oklahoma, using the Los Alamos National Laboratory portable, continuous wave/frequency modulated?continuous wave, 3-cm Doppler radar, collected close-range data at and below cloud base in six supercell tornadoes in the southern plains during the springs of 1990 and 1991. Data collection and analysis techniques are described. Wind spectra from five weak-to-strong tornadoes and from one violent tornado are presented and discussed in conjunction with simultaneous boresighted video documentation, photogrammetric analysis, and damage surveys. Maximum Doppler wind speeds of 55?105 m s?1 were found in five of the tornadoes; wind speeds as high as 120?125 m s? were found in a large tornado during an outbreak on 26 April 1991. These may be the highest wind speeds ever measured by Doppler radar and the first radar measurements of F-5 intensity wind speeds. The variation in the spectrum across the 26 April 1991 tornado is presented. Standard and mobile soundings, and surface data, used to determine the ?thermodynamic speed limit? indicate that it was usually exceeded by 50%?100%. A comparison of actual Doppler spectra with simulated spectra suggests that the maximum in radar reflectivity in supercell tornadoes lies well outside the core.