Rainfall Microstructure and Its Linkage to Structure and Evolution of Flash-Flood Producing Storms

Storms that are responsible for flash flooding have been shown to exhibit a broad range of properties in terms of structure, evolution and microphysics. In this study, we infer the dominant microphysical processes of flash-flood producing storms through the investigation on microstructure of rain rate and its temporal variations. We center this study over Goodwin Creek experimental watershed in northern Mississippi. Microstructure of rain rates is derived using observations from a Joss-Waldvogel disdrometer located in the center of the watershed. We focus on the intrinsic shapes of rain drop size distributions (DSD) without a priori functional form. Evolution and Structural properties of storms are based on storm tracking procedures that utilize the 3-D radar reflectivity observations from the KNQA (Memphis, TN) WSR-88D radar. We develop a catalogue of warm-season (April-September) rainfall events based on maximum x-minute (1 min, 15 min, 30 min) rain rates. Spectral analyses of DSD for the top 20 events exhibit a symmetrical pattern relative to the time of peak rain rates. The symmetrical pattern is accompanied by reduction (growth) in the number of small-size (large-size) rain drops before peak rain rates and a reversed pattern after peak rain rates. We further explore the roles of structural and evolutional properties of storms in determining the temporal variation of DSD. We expect to improve the understanding of the dominant mechanisms of flash-flood producing storms and provide modeling references for convective rainfall processes in atmospheric models.