Abstract
The magnitude of the Doppler velocity signature of a tornado depends on the effective width of the radar beam relative to the size of the tornado. The effective beamwidth is controlled by the antenna pattern beamwidth and the azimuthal sampling interval. Simulations of Weather Surveillance Radar-1988 Doppler (WSR-88D) velocity signatures of tornadoes, presented in this paper, show that signature resolution is greatly improved when the effective beamwidth of the radar is reduced. Improved signature resolution means that stronger signatures can be resolved at greater ranges from the radar.
Using a special recording device on the National Weather Service's Radar Operations Center's KCRI test bed radar, Archive Level I time series data were collected during the Oklahoma–Kansas tornado outbreak of 3 May 1999. Two Archive Level II meteorological datasets, each having a different effective beamwidth, were created from the Archive Level I dataset. Since the rotation rate and time interval between pulses are common for both Archive Level II datasets, the only parameter that could be changed to reduce the effective beamwidth of the KCRI data was the number of pulses, which also changed the azimuthal sampling interval. By cutting the conventional number of pulses in half for one of the Archive Level II datasets, the effective beamwidth was decreased by about a quarter and the azimuthal sampling interval was decreased from 1.0° to 0.5°. The 3 May 1999 data confirm the simulation results that stronger Doppler velocity signatures of tornadoes typically are produced when the azimuthal sampling interval, and thus the effective beamwidth, is decreased.
Corresponding author address: Dr. Rodger A. Brown, National Severe Storms Laboratory, 1313 Halley Circle, Norman, OK 73069. Email: Rodger.Brown@noaa.gov
