Wind Gradients and Variance of Doppler Spectra

Abstract

An X-band pulsed-Doppler radar having its beam fixed at an elevation angle of 3 deg, was used to measure radial velocity spectra in a light shower. Observations were made at intervals of 152 m between radar ranges of 7 and 18 km. It was found that the mean Doppler velocity, variance of the Doppler spectrum and radar reflectivity varied markedly over distances of the order of 100 m. The observed variance was below about 1 m2 sec-2 in 80 percent of the observations, but in about 4 percent of the cases, it exceeded 3m2 sec-2. An analysis of ~V/~r, the radial gradient of the mean Doppler velocity yielded a nearly Gaussian curve having a mean of 0.2 x 10-3 sec-1 and a standard deviation of 5.9 x 10-3 sec-1. The largest value observed was 3 X 10- 2 sec-1. The effects of the radial gradient of the radial wind apparently can explain about 25 percent of the observed variance of the Doppler spectrum.