Circulation and Areal Contraction Rate as Detected and Measured by Doppler Radar

Davies-Jones and Stumpf (1997) advocated using the detection and measurement of significant circulation around and areal contraction rate of a curve as a method for giving advanced warnings of tornadoes. Circulation (rate of areal contraction) is the line integral around a closed curve of velocity tangential (normal) to the curve. Circulation and areal contraction rate may be more useful than differential single-Doppler velocities in the characteristic velocity couplet for detecting and measuring the strength of convergent tornadic mesocyclones at low altitudes, because circulation and areal contraction rate are (a) less scale dependent, (b) more tolerant of noisy Doppler velocity data, (c) relatively insensitive to range and azimuth, beamwidth and location of a tornado within a sampling volume.

We will test the above method both on simulated Doppler velocity data of idealized convergent vortices and on actual NOAA National Weather Radar Testbed Phased-Array Radar located in Norman. At the conference, we will report on its success or failure compared to other methods for detecting and measuring vortices.

Reference: Davies-Jones, R., and G. J. Stumpf, 1997: On the detection and measurement of circulation and areal expansion rate with WSR-88D radars. Preprints, 28th Conf. on Radar Meteorology, Austin, TX, Amer. Meteor. Soc., 9A.2, 313-314.