Based on NCEP/NCAR daily reanalysis data and observations from 124 meteorological stations in Yunnan Province,we analyze the extreme features and low-frequency oscillation characteristics of the abnormally low temperature event in Yunnan from April to June 2022.We also investigate the evolution of the spatial config-uration of low-frequency circulation systems in the middle and lower troposphere.The results are as follows:1)In the late spring and early summer(April-June)of 2022,Yunnan experienced a rare extreme low temperature event under the backdrop of climate warming.The average temperature was the fifth lowest on record for this period since 1961 and the lowest since 1991.Average temperatures at 42 stations reached or broke histori-cal records for the same period.2)There was a significant 10-20 d period for average temperatures in Yunnan in late spring and early summer of 2022,with a variance contribution of 45.7％.This 10-20 d oscillation was close-ly related to actual temperature drops.3)During the 10-20 d low-frequency oscillation,phase 7 corresponded to the maximum temperature decrease and phase 3 to the maximum temperature increase over Yunnan.At 500 hPa,Yunnan was influenced by northerly(southerly)airflow between a low-frequency anomalous high-pressure(low-pressure)system around Lake Baikal and a low-frequency anomalous low-pressure(high-pressure)system near the Sea of Japan in phase 7(phase 3).Simultaneously,the region from eastern China to the South China Sea was mainly controlled by low-frequency northward(southward)wind at 700 hPa,which correlated with cooling(warming)areas.Yunnan was mainly under control of the low-frequency easterly(westerly)air flow and also located in the cooling(warming)area.The sea level pressure field showed an enhanced and southward-moving Siberian high-pressure system,bringing cold air from high to low latitudes,affecting temperature changes in Yun-nan,and contributing to the strong cold air process.4)At 500 hPa,low-frequency positive height anomalies prop-agated southward from high latitudes to Lake Baikal,while low-frequency positive height anomalies at middle and low latitude moved eastward from Mediterranean Sea to Lake Baikal.The synergistic effect of these two low-fre-quency wave trains facilitated the generation,strengthening,and maintenance of abnormally low temperatures in eastern China and Yunnan from April to June 2022.5)In late spring and early summer of 2022,the South Branch Westerly Trough Index and the Siberian High Pressure Index in the 10-20 d low-frequency oscillation showed the best correlation with low-frequency temperatures in Yunnan at 7 and 5 d,respectively.These indices can effec-tively predict abnormal low-temperature processes in Yunnan.
关键词
云南/2022年春末夏初(4-6月)/异常低温事件/10～20d低频振荡/环流系统
Key words
Yunnan/late spring and early summer(April-June)of 2022/abnormal low-temperature event/10-20 d low-frequency oscillation/circulation system
万方数据