甘肃省夏季异常高温及其环流特征分析

利用甘肃省62个气象观测站1960—2003年6—8月逐日最高气温、高度场和温度场格点资料,分析了高温极值、高温范围、高温持续时间的变化,并对历史上出现的四次极端高温天气过程的环流形势特征进行了分析。结果表明：甘肃河西地区极端最高气温各月之间的差异大,6月极端值最小,7月极端值最大,7月极端最高气温线性变化略呈上升趋势,6月、8月线性变化呈下降趋势,20世纪90年代极端最高气温增温不明显。河东地区极端最高气温各月之间的差异小,7月、8月的变化呈上升趋势,1995—2002年的增温明显。6月全省最大范围的高温天气出现在60年代;7月,90年代后期出现大范围高温天气的年份明显比以前增多。7月持续高温时间在90年代明显增长。100 hPa南亚高压,300 hPa暖中心、500 hPa副热带高压闭合单体控制西北地区上空,对流层上下层暖高压中心相对应,中心位置基本一致时,将出现大范围、持续性的异常高温天气。

Analyses on Extreme High Temperature and Circulation Characteristics in Summer of Gansu

The data of day-to-day maximum temperature from June to August during 1960-2003 that recorded by the 62 meteorological stations were used to the changes of the maximum value, distribution range, and continuous time of high temperature in Gansu province; the grid data of height field and temperature field of four high temperature cases were used to analyze the extreme circulation characteristics in climate history of Gansu province. The results show that, in the west of Gansu, the extreme maximum temperature differs obviously between months; the value in Jane is the lowest and that in July is the highest; there is slight increasing linear trend in July and decreasing linear trend in June and August; the increase of the maximum temperature is not evident in 1990s. In the east of Gansu, the extreme maximum temperature differs little between months; there is increasing linear trend in July and in August; the increase of the maximum temperature is evident from 1995 to 2002. The largest distribution range of high temperature in June occurred in 1960s. The number of years occurred wide range high temperature in July during the late of 1990s was more than that before, and the continuous time of high temperature in July remarkably lengthen in 1990s. High temperature weather will occur when South Asia high on 100 hPa, the warm centre on 300 hPa, and subtropical cell on 500 hPa are simultaneous over the Northwest China and the centers of them are almost vertical.