Page 81 - 《高原气象》2022年第5期

高 原 气 象 41 卷
1174

Circulation Characteristics and Conceptual Model of Rainstorm

Processes in the Eastern Foot of the Helan Mountain

CHEN Yuying 1，2，3 ，SU Yang 1，2，3 ，ZHANG Yixing 1，2，3 ，YAO Shanshan 1，2，3 ，YANG Yin 1，2，3
（1. Key Laboratory for Meteorological Disaster Monitoring and Early Warning and Risk Management of Characteristic Agriculture
in Arid Regions，CMA，Yinchuan 750002，Ningxia，China；
2. Ningxia Key Laboratory of Meteorological Disaster Prevention and Mitigation，Yinchuan 750002，Ningxia，China；
3. Ningxia Meteorological Observatory，Yinchuan 750002，Ningxia，China）

Abstract：In this study，the rainstorm processes are classified into ordinary rainstorm（50~100 mm），heavy
rainstorm（100~200 mm）and extraordinary rainstorm（more than 200 mm）according to the accumulated rain‐
fall of the rainstorm process. Then，based on 23 rainstorm processes in the eastern foot of the Helan Mountain
from 2016 to 2021，the circulation characteristics of different grades of rainstorms are investigated and the corre‐
sponding conceptual models are established. The results show that during the rainstorm processes，the westerlies
prevail in middle-high latitudes. The rainstorm area is controlled by four airflows，i. e. the 200 hPa westerly air‐
flow，the 500 hPa southwesterly airflow，the 700 hPa southerly airflow and the 850 hPa southeasterly airflow.
There is high-level jet and low-level jet in the high and low levels，respectively. The different grades of rain‐
storms are mainly caused by the different locations and intensities of the South Asia high（SAH）and the Western
Pacific Subtropical High（WPSH）. The difference in SAH and WPSH can result in the differences in low-level
temperature and humidity，and the stability of atmosphere. The baroclinity is the strongest in the middle levels
（700~500 hPa），and is relatively weak in the low levels（875~700 hPa）. The baroclinity is the strongest for ordi‐
nary rainstorm and the weakest for extraordinary rainstorm. For ordinary rainstorm processes，the fronts in the
westerlies are the most active，the WPSH is the weakest and southmost，the wet layer is the thickest，the warm
cloud layer is the thinnest，and the low-level thermal forcing and atmospheric instability is the weakest. For
heavy rainstorm processes，the dynamic forcing is weaker，the WPSH and low-jet is more northward，the low-
level thermal forcing and atmospheric instability is relatively strong，the values of convective parameters are rela‐
tively large，and the duration，area and magnitude of rainstorm are relatively large. For extraordinary rainstorm
processes，the SAH，WPSH and low-level jet are the strongest and northmost，the atmospheric instability is the
strongest，the wet layer is the thinnest，and the warm cloud layer is the thickest. The values of convective param‐
eters and vertical wind shear in extraordinary rainstorm processes are 1~3 times that of ordinary and heavy rain‐
storm processes. The joint effects of the northward advancing low-level jet and the topography of the Helan
Mountain favor the occurrence of local rainstorms in the eastern foot of the Helan Mountain.
Key words：Different grades of rainstorms；baroclinicity；circulation situation；thermal and dynamic features；
conceptual model