Characteristics of Raindrop Falling Process at the Mount Huang

Utilizing raindrop spectrum data recorded by PARSIVEL of April-Octomber from 2011 to 2012 at the top and foot of the Mount Huang, 17 precipitation cases are collected, which divided into convective cloud precipitation and stratiform cloud precipitation. Characteristics of raindrop spectrum in different height and cloud from 17 precipitation cases are analyzed.Observed results show that the average concentration of raindrops at the top of the mountain is higher than that at the foot of the mountain in both convective cloud and stratiform cloud precipitation, the average peak diameter and the average mass median diameter both increase during falling process, but average intensity and radar reflectivity both have a smaller change. Neither convective cloud nor stratiform cloud raindrop spectrum distribution broadens from top to foot of the Mount Huang, but the spectrum shapes of raindrop change from M-P (Marshall-Palmer) to Gamma. Raindrop loses at most bins when falling from top to foot of the mountain, the maximum loss appears at the third bin of raindrop spectrum, with the loss percentage exceeding 50%. The concentration of bigger raindrop of stratiform cloud begins at the 11th bin (with feature diameter of 1.375 mm) and convective cloud raindrop begin at the 13th bin (with feature diameter of 1.875 mm) increase during falling process. The increase amplitude is lower than 10% except the 12th bin (with features diameter of 1.625 mm) and the 13th bin of stratiform cloud raindrop, and the increase at these two bins are 10.8% and 11.9%, respectively. Evaporation accompanies with the whole falling process, which has bigger effects on small raindrops than big ones, leading to lower concentration of smaller raindrop at the foot of the mountain. These losses gradually reduce along with raindrop diameter increasing due to effects of coagulation process of raindrop become stronger along with raindrop diameter increasing. Therefore, these changes occurring during falling process may be caused by both evaporation and coagulation process of raindrop.