Page 221 - 《高原气象》2022年第5期

高 原 气 象 41 卷
1314

Relationship between Extreme Low Temperature Events and Atmospheric

Circulation in Yunnan during Winter Half Year

1
JIN Yan ，YAN Hongming ，ZHANG Maosong ，MA Siyuan ，KUANG Xueyuan 2
1
1
1
（1. Yunnan Climate Centre，Kunming 650032，Yunnan，China；
2. School of Atmospheric Sciences in Nanjing University，Nanjing 210093 Jiangsu，China）
Abstract：The regional extreme low temperature events（RELTE）in winter half year of Yunnan from 1961 to
2019 are examined by using a simplified objective identification method. The results are shown as following：the
frequency of Yunnan RELTE、the cumulative impact intensity and the number of stations affected by the Yunnan
RELTE showed a trend of decline in the past 59 years，but the frequency of extreme events and the number of
sites affected increased in recent 10 years. The RELTE duration mainly ranged from 1 to 4 days，the occurrence
probability was higher in November and March of the winter half year. The possibility of RELTE was higher in
the eastern part of Yunnan，but in the narrow area west of Nujiang River the possibility was lower. Since the mid-
1980s，there was no year in which all three seasons of winter half year RELTE are occurred in Yunnan. The fre‐
quency of late autumn RELTE decreased rapidly and there aren’t occur in recent 10 years. From the analysis of
circulation characteristics，the atmospheric circulations affecting the Yunnan RELTE are different in different sea‐
sons：In late autumn，the Rossby wave over North America are spreaded eastward on the upper 300 hPa，the
500 hPa atmospheric pressure field over East Asia is "high in the west and low in the east" and the 850 hPa north‐
east wind leads the cold advection southward，which easily causes the Yunnan RELTE to be active. The winter
RELTE are caused by the eastward Rossby wave over the Azores Islands in the North Atlantic Ocean at 300 hPa，
the "high in the north and low in the south" air pressure field over East Asia at 500 hPa，the cold advection guid‐
ed by the mid-latitude east wind at 850 hPa. In early spring，the Rossby wave of 300 hPa on the northeast Pacific
Ocean travels eastward from the Scandinavian Peninsula to East Asia and the pressure field of 500 hPa on East
Asia is "high in the north and low in the south"，east wind and north wind of 850 hPa lead the cold advection
southward together and meets southern branch trough in Yunnan，which is prone to RELTE.
Key words：Yunnan；winter half year；extreme low temperature events；cold advection；Rossby wave