MICROPHYSICAL CHARACTERISTICS OF THE RAINDROP SIZE DISTRIBUTION IN TYPHOON MORAKOT (2009)

Microphysical characteristics of the raindrop size distribution (RSD) in Typhoon Morakot (2009) have been studied through the PARSIVEL disdrometer measurements at one site in Fujian province, China during the passage of the storm from 7 to 10 August 2009. The time evolution of the RSD reveals different segments of the storm. Significant difference was observed in the microphysical characteristics between the outer rainband and the eyewall; the eyewall precipitation had a broader size distribution (a smaller slope) than the outer rainband and eye region. The outer rainband and the eye region produced stratiform rains while the eyewall precipitation was convective or mixed stratiform-convective. The RSD was typically characterized by a single peak distribution and well represented by the gamma distribution. The relations between the shape (μ) and slope (Λ) of the gamma distribution and between the reflectivity (Z) and rainfall rate (R) have been investigated. Based on the NW–CDm relationships, we suggest that the stratiform rain for the outer rainband and the eye region was formed by the melting of graupel or rimed ice particles, which likely originated from the eyewall clouds.