Analysis of raindrop spectrum characteristics for a heavy rain event caused by typhoon Haikui (No.1211) in Anhui

Abstract

Using conventional meteorological observations,observational data from regional automatic weather stations,NCEP reanalysis data and the raindrop spectrum data from ground-based disdrometers at Chuzhou station and the Shandi station at the foot of Huang Mount,we have performed an analysis of the precipitation characteristics and circulation background for the heavy rain event caused by typhoon Haikui from August 8 to 9 in 2012, with focus on the raindrop size distribution characteristics in the two stages of this event,that is,the first stage of precipitation caused by typhoon itself and the second stage caused by cold air intrusion. The results are as follows. (1) During this precipitation event,both the averaged spectrum widths are large at Chuzhou station and the Shandi station. There are big raindrops with diameter from 6 mm to 8 mm. But there is higher raindrop concentration and smaller raindrop size at the Shandi station. (2) During the whole precipitation event,the averaged spectrum at Chuzhou station is close to the raindrop pattern of the latter stage,while the averaged spectrum at the Shandi station is close to the raindrop pattern of the previous stage. The raindrop spectrum patterns at the two stations at different precipitation intensities are similar basically. And with the increase of precipitation intensity,the spectral width and raindrop concentration increase at the two stations. (3) At the different stages of this event,there are the different raindrop spectrum characteristics at Chuzhou station and the Shandi station. In the previous stage,the means of rainfall intensity (R),raindrop mass weighted mean diameter (Dm) and standardized raindrop number concentration (Nw) at Chuzhou station are all smaller than those at the Shandi station. In the latter stage,R and Dm at Chuzhou station increase significantly,which are larger than those at the Shandi station. (4) From the previous stage to the latter stage,the raindrop spectrum varies significantly at Chuzhou station,showing that the spectrum width increases from narrow to wide and raindrop number concentrations increase with increasing of the raindrop size. Meanwhile,there is little difference in the raindrop pattern at the Shandi station,showing that the spectrum width changes from wide to narrow,and the raindrop concentrations increase first and then decrease with the increase of raindrop size and the raindrop number concentrations increase first and then decrease with the increase of raindrop size.

Keywords

• typhoon
• heavy rain
• raindrop size distribution
• raindrop concentration
• microphysical characteristics