关键词: 极端低温事件, 冬季, 突变, 周期

Abstract: Using 21-station uniform minimum temperature over Beijing and its surrounding area, the thresholds of daily extreme low temperature were determined for different stations. The spatial and temporal variation characteristics of the frequency and intensity for extreme low temperature events and abrupt and periodic detection in winter were analyzed. The results showed that the extreme low temperature days have a trend of decreasing over Beijing and its surrounding area during 1958-2006. The highest value of the decreasing rate for extreme low temperature is located in Beijing, Baoding, Shijiazhuang and Xingtai. It’s about -11d/49y in most areas. The frequency of the extreme low temperature in regional average decreased rapidly in the early of 1970s. In recent 49 years, the minimum temperature is higher than -20℃ over Tanggu district in Tianjin, the eastern area of Cangzhou and the southern area of Xingtai in Hebei Province. It is lower than -20℃ over the rest of the whole area. The linear gradient of the change of extreme minimum temperature is in northwest southeast direction. The increase trend of the variation for extreme minimum temperature is obvious. The increase extent over Xingtai in Hebei Province is the largest; it increases by 1.4℃/10y. The variability is greater than 1.0℃/10y in the direction of Chengde BeijingShijiazhuang. The frequencies of extreme low temperature in winter have the trend of decreasing since about 1980 and have an abrupt phenomenon, but haven’t the same abrupt time. The abrupt time occurred in 1980s for the frequencies of extreme low temperature over Beijing Tianjin and the southern part of Hebei province, while it occurred in the late 1970s over the northern and eastern area of Hebei province. It was also found that the vibration period of 7~9 years are displayed in all the areas. This research has important significance for winter installation and agricultural production.

Key words: Extreme low temperature, Winter, Abrupt time, Period