Variance Spectrum Analysis of Doppler Radar Observations in Continuous Precipitation

Abstract

A continuous record of precipitation falling through a fixed volume in space was obtained by means of a vertically-pointing pulsed-Doppler radar during a period of continuous precipitation. The range gate was held fixed at an altitude of 910 m above the ground. The output of the radar gave the power returned in several adjacent velocity intervals, from which the drop size distribution and liquid water content were calculated. Variance spectra for power in selected velocity channels, total liquid water, and reflectivity were computed. The results revealed that despite the uniformity of radar reflectivity at elevations much below the melting layer, a good deal of structure was still evident in the time (space) variations in number of drops of given size. The variance spectra for concentration of drops falling at 7 m sec?1 (about 2 mm drop diameter) revealed significant modes at wavelengths of 2?3 km, and about 350?800 m, which support other evidence of organized atmospheric activity at these scales.