PNNL

Abstract

This study compared drop size distributions (DSD) measurements on the surface, the corresponding properties, and precipitation modes among three deep convective regions within the Americas. The measurements compilation corresponds to two sites in midlatitudes: the U.S. Southern Great Plains and Córdoba Province in subtropical South America, and, to one site in the tropics: Manacapuru in central Amazonia, all where intense rain-producing systems contribute to the majority of rainfall in the Americas’ largest river basins. This compilation included two types of disdrometers (Parsivel and 2D-Video Disdrometer) used at the midlatitudes sites, and 1 type of disdrometer (Parsivel) deployed at the tropics site. The distributions of physical parameters (such as rain rate R, mass-weighted mean diameter Dm, and normalized droplet concentration Nw) for the raindrop spectra without rainfall mode classification seem similar except for much broader Nw distributions at Córdoba. It then classifies the raindrop spectra into a light precipitation mode and a precipitation mode using a cutoff at 0.5 mm hr??1 based on previous studies characterizing the full drop size spectra. These rain modes segregated are potentially unique relative to previously studied terrain-influenced sites. In the light precipitation and precipitation modes, the dominant higher frequency observed in a broad distribution of Nw in both types of disdrometers, and the identification of shallow light precipitation in vertically-pointing cloud radar data, represent unique characteristics of the Córdoba site relative to the others. As a result, the co-variability between DSD physical parameters indicates that the precipitation observed at Córdoba may confound existing drop size distribution methods of determining rain type.