Abstract: Based on the daily minimum temperature observation data in southeast of Gansu Province during 1969-2018, the variation of extreme low temperature events was analyzed, then 74 circulation characteristic quantities from National Climate Center were used to research the circulation system affecting the extreme low temperature events. The results are as follows: (1) The frequency of annual extreme low temperature events in southeast of Gansu Province reduced obviously with a rate of 2.3 d·(10 a)-1 in the last 50 years, and the reduction was most significant in summer and slowest in winter. There was an abrupt change of extreme low temperature days in 1987, after the abrupt change, the frequency of extreme low temperature events was relatively lower. (2) Compared with the climatic mean, the intensity of extreme low temperature events tended to increase, before 1987, the low temperature intensity anomaly increased with a rate of 0.2 ℃·(10 a)-1, while after 1987, the extrem low temperature intensity anomaly increased with a rate of 1.2 ℃·(10 a)-1. (3) The intensity of extreme low temperature in spring, summer, autumn and winter mainly ranged from -5.0～5.0 ℃, 10.0～15.0 ℃, -5.0～10.0 ℃, -20.0～-10.0 ℃, and the occurrence frequencies were 61.9%, 90.1%, 73.4% and 73.1%, respectively. (4) There was a positive correlation between extreme low temperature events and Eurasian meridional circulation in southeast of Gansu Province. The extreme low temperature events was related with cold air, the area index of western Pacific subtropical high and the intensity of polar vorticity center in the northern hemisphere in winter, while it was related with subtropical high northern boundary of South China sea, subtropical high northern boundary of the western Pacific and polar vorticity intensity of the Pacific in spring. The composited analysis of geopotential height fields indicated that Mongolia was a cold high pressure center on ground, and polar vorticity center was located in the eastern hemisphere from 500 hPa to 100 hPa, the westerly belt prevailed meridional circulation, and east Asian large trough in the westerly belt was deep and westward, the region of southeast of Gansu was controlled by strong northwest airflow after the trough, which was favourable to forming extreme low temperature events.

Key words: southeast of Gansu Province, extreme low temperature events, climate change, circulation indexes

摘要： 利用1969—2018年陇东南地区31个气象站逐日最低气温资料，分析陇东南地区极端低温事件的演变特征，并采用国家气候中心提供的74项环流特征量，对影响极端低温事件的环流系统进行研究。结果表明：（1）陇东南地区近50 a极端低温日数以2.3 d·(10 a)-1的趋势减少，其中夏季减少最显著，冬季减少最缓慢；1987年为极端低温日数突变点，突变后极端低温事件急剧减少。（2）相较于1981—2010年气候平均值，陇东南地区近50 a极端低温呈增强趋势，突变前后极端低温强度距平以每10 a升高0.2 ℃变为每10 a降低1.2 ℃，且突变后冬春季极端低温强度降低最显著。（3）春季、夏季、秋季、冬季极端低温的强度范围主要在-5.0～5.0 ℃、5.0～15.0 ℃、-5.0～10.0 ℃、-20.0～-10.0 ℃，出现频率分别达61.9%、90.1%、73.4%、73.1%。（4）陇东南地区极端低温事件与欧亚经向环流关系密切，冬季还与冷空气、西太平洋副高面积指数、北半球极涡中心强度有关，春季与南海副高北界、西太平洋副高北界、太平洋区极涡强度有关。当蒙古为冷高压中心、西风带经向环流明显、东亚大槽深厚且位置偏西、极涡偏向于东半球时，陇东南地区受槽后强盛西北气流控制，易出现较强极端低温事件。

关键词: 陇东南地区, 极端低温事件, 气候变化, 环流指数