Page 139 - 《高原气象》2021年第5期

高 原 气 象 40 卷
1100

Analysis of Difference in Distribution of Rainstorms in the Later Two

Stages of Northward-Moving Typhoon Ampil

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CHEN Hong ，YANG Xiaojun ，YI Xiaoyuan ，WEI Yinghua ，YANG Yang ，ZHANG Qing ，SUN Jing 2
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（1. Tianjin Meteorological Observatory，Tianjin 300074，China；
2. Shandong Meteorological Observatory，Jinan 250000，Shandong，China）
Abstract：Based on China Meteorological Administration（CMA）typhoon path data，surface-observed hourly
data，NCEP/NCAR（1°×1°）re-analysis data，black-body temperature equivalent（TBB）of FY-2F satellite data，
radar data，and conventional observation data，the reason for the distribution characteristics of the asymmetry of
the later two stages of northward-moving typhoon Ampil（1810）was analyzed. The intensity of the typhoon re‐
mained unchanged when Ampil went northward，but it caused the Shandong torrential rain to locate on the east
side of the typhoon track，while the Tianjin torrential rain located on the west side of the track. The result indicat‐
ed that after Typhoon Ampil went northward，the cloud system around it developed into an asymmetrically dis‐
tributed cloud system，with obvious asymmetry in the structure of rainfall and circulation. In the two heavy-rain‐
fall areas that located in Shandong and Tianjin，the enhanced development of rainfall was consistent with the de‐
velopment characteristics of convective cloud clusters. Short-term heavy-rainfall sites with low centroids were
distributed in the high-value area of the TBB gradient. When the typhoon was in Shandong，mesoscale cloud
clusters and heavy rainfall mainly located in the central of Shandong，east of the typhoon path，because weak
vertical wind shear was conducive to maintaining the heart-warming structure and strength of the typhoon. The
high-temperature and humidity environment carried by the typhoon itself caused the conditional symmetry and in‐
stability of the lower troposphere，and triggered short-term heavy rainfall on the east side of the typhoon. The
center of heavy rain was affected by the combined effects of positive vorticity，vertical velocity，water-vapor
convergence，and topography of Mount Tai. After the typhoon entered Tianjin，cold air infiltrated from the west‐
erly trough，infiltrating the typhoon circulation from the northwest side，causing the intersection of cold and
warm air. This additionally inspired an asymmetric mesoscale system，leading to vertical wind shear and positive
vorticity increasing significantly，resulting in high-level divergence and low-level convergence，causing obvious
suction. Together，these events caused strong upward movement on the west side of the typhoon and the thick‐
ness of unstable stratification increased significantly，providing favorable conditions for the development of me‐
soscale systems. At the same time，the southeast jet in the lower troposphere caused water vapor to be replen‐
ished after passing through the Bohai Sea，forming an obvious belt-shaped water-vapor convergence zone on the
northwest side of the typhoon. This convergence zone led to the band-shaped mesoscale cloud cluster of cyclonic
circulation that developed in the northwestern side of the typhoon cloud system at the junction of Beijing and
Tianjin. Together，these events led to short-term（5-h duration）heavy rainfall on the northwest side of the ty‐
phoon.
Key words：Typhoon；mesoscale cloud clusters；unstable stratification；water vapor transport