Objective Classification of Precipitating Convective Regimes Using a Weather Radar in Darwin, Australia

Abstract

A clustering algorithm was applied to Frequency with Altitude Diagrams (FADs) derived from 4 yr of hourly radar data to objectively define four tropical precipitation regimes that occur during the wet season over Darwin Australia. The precipitation regimes defined are distinguished in terms of convective intensity, presence of stratiform precipitation, and precipitation coverage. Regime 1 consists of patchy convection of medium intensity and low area coverage, and regime 2 contains strong convection with relatively small area coverage. Regime 3 is composed of weak convection with large area coverage and large stratiform regions, and regime 4 contains strong convection with large area coverage and large stratiform regions. Analysis of the seasonal cycle, diurnal cycle, and regime occurrence as a function of monsoon activity all provide insight into the different physical character of the precipitation regimes. Two of the regimes exhibit a diurnal cycle with a peak in the afternoon, while the other two show a peak in their frequency of occurrence in the early morning. The different character of the regimes is also confirmed by the varying contributions that convective and stratiform rainfall make to the overall within-regime precipitation.