Page 115 - 《高原气象》2022年第5期

高 原 气 象 41 卷
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warm and wet airflow that strengthened at night along the steep slope of the Chuanxi Plateau. The convective sys‐
tem appeared as a slender linear pattern along the plateau slope at the initial stage，then it was affected by the in‐
teraction between the convective cold pool along the edge of the basin and the low-level warm and wet southeast
airflow. The mature MCSs（Meso-scale Convective Systems）manifested as a rightward shifting storm with back‐
ward propagation characteristics，which developed toward the middle of the basin and gradually moved away
from the plateau topography. As the warm and wet inflow on the front side of the convection system significantly
weakened，the convection system weakened and dissipated. The heavy rain process occurred in the central of si‐
chuan basin from 29th June to 1st July（hereinafter referred to the Central Basin Type case）was a long-life histo‐
ry convective precipitation process，which was related to the evolution of the southwest vortex system. The con‐
vective system was triggered on the baroclinic front area outside the low-level shallow warm vortex（below 850
hPa）along the 700 hPa warm and wet tongue，and it was organized into a linear convection system along the left
side of the low-level jet axis in the middle troposphere. After convection was generated，through the interaction
between the outflow of the shallow cold pool generated from the southern part of the convective system and ambi‐
ent warm and humid air currents，new convective systems were triggered and developed towards the area with
high value θse. The convection system gradually evolved from "linear" to "arc-shaped". Later，as the vortex air‐
flow tilted toward the middle troposphere，new convetions were continously trigerred by cyclonic convergent air‐
flow on the pseudo-equivalent temperature front area，then the convective systems gradually evolved into a spiral
rain belt distribution in the middle of the basin. As the low vortex centers in the middle and low troposphere grad‐
ually overlap with the height，the spiral convective rainband gradually shrinked toward the center of the low vor‐
tex and eventually disappeared. The heavy rain process occurred around the Sichuan Basin from 4th to 5th July
（hereinafter referred to the Peripheral Basin Type case）was directly related to the process of cold air crossing the
Qinling-Daba Mountains and intruding into the basin from the northwest side of the basin. The convection system
was first triggered by the cold air along the steep topography of the western edge of the basin. As the cold air ad‐
vanced to the south，convection systems moved to the topographical edge of the southwestern part of the basin.
As cold air in the basin accumulated in the western part of the basin and expanded eastward in the lower layer，
the convection in the middle troposphere above the shallow cold pad is unstable and warm Under the uplift of wet
shear，the eastern part of the basin triggered an elevated thunderstorm and developed and organized along the
shear line.
Key words：Sichuan Basin；heavy rain；meso-scale convective system；convective cold pool