The N0 Jump of Raindrop Spectra

Abstract

Raindrop spectra are measured with an electromechanical raindrop spectrometer, responding to drops >0.3 mm in diameter. The radar reflectivity profile is measured simultaneously with a 5-cm vertically pointing radar. Measured raindrop spectra are described by two parameters, N0 and A, the intercept and slope respectively of an exponential distribution having the same water content and radar reflectivity factor as the observed sample. Sudden variations in the raindrop spectra and in the reflectivity profile during widespread rain situations were observed. Due to the parameterization used, these sudden variations of the spectra can be recognized easily as N0 jumps. It seems that the N0 jumps indicate the transition from one mesoscale area within the precipitation field to another. The characteristics of the N0 jumps and the related cloud physics are discussed. An empirical model is proposed for the relation between the type of raindrop spectra and the convective activity of the precipitating air mass.