Page 88 - 《高原气象》2025年第5期

高 原 气 象 44 卷
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mosphere interaction in the Qinghai-Xizang Plateau， little attention has been paid to the dependence of lake ef‐
fect on background circulation to understand the mechanism of lake affecting extreme precipitation. To further un‐
derstand the mechanism of lake influence on extreme precipitation， this study objectively classifies the dominant
synoptic patterns responsible for the regional extreme precipitation events in autumn over the central Qinghai-
Xizang Plateau with lakes densely distributed to analyze the characteristics and differences of lake effects under
different dominant synoptic patterns. Based on the CMFD precipitation data and ERA5 reanalysis data during
1979 to 2018， 1358 regional extreme precipitation events were detected in autumn over the central Qinghai-
Xizang Plateau， and it was found that the regional extreme precipitation events contributed more than 40% of the
total autumn precipitation in most parts of the central Qinghai-Xizang Plateau with the large centers of regional
extreme precipitation amount mainly concentrated in the Nam co basin and the small lakes in the north， that is al‐
so the region with high occurrence probability of extreme precipitation when regional extreme precipitation event
occurs. Then， the spectral clustering method was used to analyze the atmospheric circulation over the central Qin‐
ghai-Xizang Plateau during the regional extreme precipitation events and identified three dominant synoptic pat‐
terns responsible for the regional extreme precipitation events in autumn over the central Qinghai-Xizang Pla‐
teau： precipitation in the southern mountainous areas caused by weak convergence airflow （P1 type）， precipita‐
tion in the northeast downstream under the control of monsoonal southwest airflow （P2 type）， and precipitation
near lakes under the influence of southwest airflow in front of the westerly trough （P3 type）. They lead to
48. 8%， 42. 3% and 8. 8% of the total occurrences of regional extreme precipitation events in autumn， respec‐
tively. P1 and P2 types mainly occur in September， and P3 type mainly occurs in October. The physical mecha‐
nism of the regional extreme precipitation occurrences is explained by analyzing the high and low level configura‐
tion of large-scale circulation fields and their anomalies under different synoptic patterns. Furthermore， multiple
sensitivity experiments were conducted to reveal the relative importance of the influence of lake clusters in the
central Qinghai-Xizang Plateau on regional extreme precipitation events under different synoptic patterns， and
found that the lake clusters can lead to the precipitation amount averaged over the central Qinghai-Xizang Plateau
reduced by 2. 37%， increased by 12. 11% and increased by 138. 37% under the P1， P2 and P3 types， respective‐
ly. The lake effect under the P3 type is the most significant among the three synoptic types， making it a synoptic
pattern prone to lake effect. Further mechanistic analysis shows that the enhancement of low-level instability and
water vapor convergence over the lake and surroundings areas induced by the heating and moistening effect of
lake play an important role in the formation of the regional extreme precipitation under the synoptic pattern P3.
This research has identified the dominant synoptic patterns responsible for the regional extreme precipitation
events over the central Qinghai-Xizang Plateau in autumn and revealed the relative importance of lake effects on
regional extreme precipitation under different dominant synoptic patterns， providing necessary reference for fur‐
ther improving the prediction level of regional extreme precipitation.
Key words： Central Qinghai-Xizang Plateau； regional extreme precipitation； synoptic patterns； lake effect