Page 125 - 《高原气象》2021年第5期

高 原 气 象 40 卷
1086

Characteristics of the Raindrop Size Distribution during a Short-time

Heavy Rainfall and a Squall Line Accompanied by Hail

1，2
WANG Jun ，WANG Wenqing ，WANG Hong ，ZHANG Qiuchen ，GONG Dianli 1，2
1，2
1，2
1，2
（1. Key Laboratory for Meteorological Disaster Prevention and Mitigation of Shandong，Jinan 250031，Shandong，China；
2. Shandong Weather Modification Office，Jinan 250031，Shandong，China）
Abstract：To better understand the differences of rain drop size distribution（DSD）and its integral parameters，
such as intercept parameter，volume weight diameter，rain intensity and radar reflectivity factor，between warm
rainfall and cold rainfall processes，the characteristics of rain DSD during a heavy rainfall and a squall line ac‐
companied by hail（rain intensity higher than 10 mm·h ）are analyzed based on data observed by Parsivel dis‐
-1
drometers and CINRADA/SA Doppler radars. The results are shown as follows.（1）The DSD of the convective
type in heavy rainfall includes single-peak spectrum（peak diameter between 0. 2 and 0. 3 mm），double peak
spectrum（peak diameter being 0. 9 or 2. 0 mm）and multi-peak spectrum（the second and third peaks appear si‐
multaneously when particle diameter is 1. 0 mm and 2. 0 mm），indicating that the coalescence and collision-
breakup of raindrops in warm rainfall are dominant processes. The intercept parameter and the mean mass-weight‐
ed diameter（lgN -D ）of the normalized Gamma function show the continental convective characteristics of rain
m
w
DSD during the heavy rainfall. The Z-R relationship is close to that of the new generation Doppler radar. Al‐
though the heavy rain is fully developed in the high-altitude cold rainfall processes，the collision-coalescence and
breakup in the warm rainfall have enough time to operate owing to the high position of 0 ℃，and the equilibrium
DSD appears.（2）The DSD of the convective precipitation accompanied by hail is mainly single-peak spectrum
（peak diameter between 0. 2 and 0. 7mm），lacks the second peak with larger diameter，has more small and large
diameter particles，and the curve of DSD larger than the peak diameter is a concave upward. The distribution of
lgN -D shows a larger D compared with the DSD of continental convective precipitation，while the Z-R rela‐
m
w
m
tionship has a larger index and coefficient，deviating from that of the new generation Doppler radar. The differ‐
ences between cold rainfall and warm rainfall processes lead to the obvious differences between ground DSD and
integral parameters. In the precipitation process accompanied by hail，ice particles such as graupel and hail con‐
stantly melt and breakup in the falling process，leading to the large number of small and large raindrop on the
ground. Therefore，the differences in microphysical processes bring about different characteristics of DSD.
（3）When different order moments are used to calculate the exponential bn，it is necessary to make a reasonable
choice according to the characteristics of DSD. The difference of number density between large，medium and
small particles will lead to the great difference of the variation of different order moments with rain intensity. The
analysis of a scaling law formalism shows that the general distribution function g（x）for the DSD of the heavy
rainfall can be exponential function or Gamma function with shape factor less than 1. 0，while the general distri‐
bution function g（x）for the DSD of the convective precipitation accompanied by hail is more suitable for Gam‐
ma function with shape factor less than 0.
Key words：Heavy rainfall；hail；raindrop size distribution；scaling law formalism；general distribution func‐
tion