Study finds variation in raindrop size distributions according to seasons and rain types

A distinguished scientist in China has revealed through a study that precipitation and raindrop size distribution (DSD) characteristics in East China vary across seasons and rain types.

The findings by Prof. Kun Zhao, Distinguished Scientist at Nanjing University, and colleagues is based on data from the observations of a two-dimensional video disdrometer (2DVD) and a vertically pointing micro rain radar (MRR). The findings about seasonal variations of rainfall microphysics in East China published in Advances of Atmospheric Sciences.

For the study researchers have been conducting a field campaign named “Observation, Prediction and Analysis of Severe Convection of China” (OPACC) in the Yangtze-Huaihe River Basin since May 2014. As of June 2016, two years of continuous 2DVD and MRR data had been obtained, which could then be used to reveal the DSD characteristics across different rain types and seasons.

Scientists note that summer rainfall is dominated by convective rain (77.5%), while during the other seasons the contribution of stratiform rain to rainfall amount is equal to or even larger than that of convective rain. A relatively larger raindrop diameter and highest concentration of raindrops during summer result in the highest mean rain rate among the four seasons, followed by spring and autumn, and winter rainfall is characterized by the lowest raindrop concentration, thus having the lowest mean rain rate. Overall, convective rain exhibits a maritime nature, with high concentrations of small drops throughout the year. Localized rainfall estimators were derived for further application purposes, among which the rainfall kinetic-energy-mass-weighted-diameter relationship was proposed for the first time.

Prof. Zhao believes that the new findings hold the potential to improve the accuracy of rainfall kinetic energy estimation, DSD retrieval, and quantitative precipitation estimation in this specific region.

“To better improve the microphysics parameterization in numerical weather precipitation models for more accurate quantitative precipitation forecasting, the physical or microphysical processes resulting in the differences of seasonal precipitation microphysics are worthy of further study. Advanced GPM and/or polarimetric radar observations would be helpful, and we plan to conduct further research along these lines in the future”, he said.