Measurement of Vertical Velocities in Convective Clouds by Means of Pulsed-Doppler Radar

Abstract

Observations of a thunderstorm by means of a vertically pointing pulsed-Doppler radar were used to compare two presently used schemes for estimating vertical air velocity in convective clouds. It was found that the air velocity given by the positive bound of the Doppler velocity spectrum and the air velocity obtained by the use of a procedure proposed by R. R. Rogers in 1964 were well correlated. In regions where raindrops would be expected, the standard deviation of the difference of the two velocity estimates was 1.2 m sec?1. Part of the differences can be attributed to uncertainties in the size distribution of the scatterers and to difficulties in establishing the correct upper bound of the Doppler spectrum. This analysis concludes, in the rain-filled region of this cloud, that the effects of turbulence on the Doppler spectrum were small. The observations show that the vertical velocity and radar reflectivity fields in some convective clouds are much more variable than they are usually assumed to be by cloud physicists and dynamicists. Large differences of cloud properties were observed over distances of 500?1000 m.