Automatic Detection of Mesocyclonic Shear with Doppler Radar

Abstract

A region of high wind shear always accompanies large intense tornadoes. Such shear is readily measured by Doppler radar and thus can be used to identify regions in storms where tornadoes are likely to form. An algorithm developed at the National Severe Storms Laboratory uses decision thresholds to discriminate between mesocyclone shear and other shears not associated with organized circulatory flow. A detailed test of these and other thresholds was made by testing the algorithm on storms with and without mesocyclones. The algorithm requires storage and calculations on two consecutive radials of data, and thus is suitable for real time implementation. We have applied the algorithm to data from sixteen mesocyclones to evaluate detection performance. The probability of false alarm was 10%, and the probability of detection was 90%. The algorithm accounts for distortion of the shear pattern caused by the large antenna beam dimensions at long ranges.