Characteristics of the raindrop size distribution for freezing precipitation observed in southern China

Abstract

Freezing precipitation (i.e., freezing rain or freezing drizzle) is an extremely hazardous weather that can cause severe socioeconomic loss and compromise human safety. To better document and understand the microphysics of this type of precipitation, drop size spectra were collected with an optical disdrometer during a freezing precipitation event on 27 January 2008 in southern China. The drop size distribution (DSD) characteristics, the correlations between the shape (μ), slope (Λ), and intercept (N 0) of the gamma distribution, and the relations between the reflectivity (Z) and rainfall rate (R) have been investigated. It was found that the DSDs of freezing precipitation were characterized by weak stratiform rain with a small mass-weighted diameter (D m, 0.63 mm) and a large normalized intercept (N w, 4.25 log 10 mm -1 m -3). This indicated that freezing precipitation was not formed by the melting of larger, dry snowflakes but by the melting of smaller, rimed ice particles. Furthermore, the derived μ-Λ, N 0 -μ, and Z-R relations are distinctly different from the convective rains or tropical stratiform rains reported in the literature. Copyright 2011 by the American Geophysical Union.