• CN 62-1175/P
• ISSN 1006-7639

Journal of Arid Meteorology ›› 2020, Vol. 38 ›› Issue (6): 900-908.

### Characteristics of Extreme Low Temperature Events in Southeast of Gansu Province in Recent 50 Years and Their Circulation Background

HAO Hui1, GUO Qingyuan2, MA Pengcheng1, WANG Lina1,LIU Liwei3, LIU Weiping3, LI Changde1#br#

1. 1. Pingliang Meteorological Bureau of Gansu Province, Pingliang 744000, Gansu, China;
2. Xi’an Meteorological Bureau of Shaanxi Province, Xi’an 710016, China;
3. Lanzhou Regional Climate Center of Gansu Province, Lanzhou 730020, China
• Online:2020-12-31 Published:2021-01-06

### 陇东南地区近50 a极端低温事件演变特征及环流背景

1. 1.甘肃省平凉市气象局，甘肃平凉744000；2.陕西省西安市气象局，
陕西西安710016；3.甘肃省兰州区域气候中心，甘肃兰州730020
• 通讯作者: 郭庆元（1985— ），女，工程师，主要从事天气预报、环境气象等相关研究. E-mail： 8040053@qq.com。
• 作者简介:赵慧（1990— ），女，硕士，工程师，主要研究方向为中短期天气预报. E-mail： zhaohui12@lzu.edu.cn。

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.