西安市近59年高温天气气候特征

目的]研究西安市近59年高温天气气候特征。方法]利用西安观测站1951～2009年逐日最高气温资料,采用统计方法研究不同强度高温天气的气候特征及影响高温天气的高空环流形势。结果]近59年西安市平均每年有22.95个高温日,4月下旬～9月上旬均可出现;高温日以7月下旬最多,6月下旬次之;≥38.0℃的酷热天6月下旬和7月下旬出现2个峰值;≥40.0℃特热天6月中下旬最多,7月各旬次之,8月几乎不会出现。高温日、酷热日、特热日天气过程的年代际变化均呈现多—少—多的趋势,20世纪50～60年代多,70～80年代少,90年代后又复增多。年极端最高气温多出现在6月中下旬,其次在7月下旬,其年代际变化呈高—低—高的趋势。高温天气过程7月份出现次数最多,持续时间也最长;酷热天一般持续2 d,≥40.0℃的特热天气很少持续出现。高温天气的环流形势大致可归结为大陆高压控制型、副高控制型、带状高压控制型及西北气流控制型4类。结论]该研究为高温天气预报预警提供参考依据。

Characteristics of High Temperature in Recent 59 Years in Xi' an City

Objective] The aim was to study the characteristics of high temperature in Xi'an City in recent 59 years.Method] By dint of daily highest temperature in Xi'an observatory,the climate characteristics of high temperature at different intensity and the high attitude circulation were studied by statistics method.Result] In recent 59 years,there were 22.95 high temperature days each year in average in Xi'an City and it appeared from the last ten days of April to the first ten days of September.Most high temperature days occurred in the last ten days of July,followed by that in the last ten days of June.There were two peak values in the last ten days of June and last ten days of July when temperature ≥38.0 ℃.For the hottest day,it occurred most in the last twenty days of June and then in the July,barely in the August.The interannual changes of the high temperature day,hot day and hottest day showed one-little and one-much trend.It was much from 1950s to 1960s,from 1970s to 1980s and then grew more after 1990s.The annual extreme highest temperature took place in the last twenty days of June,and then in the last ten days of July.Its interannual changes showed high-low-high trend.The high temperature appeared most in July and also lasted for the longest duration.The hot day lasted for two days.The most hot day of ≥40.0 ℃ seldom appear.The circulation of high temperature was generally in four categories: continental high pressure controlling type,subtropical high controlling type,strip high pressure controlling type and northwest airstream controlling types.Conclusion] The study provided reference for the forecast and pre-warning of high temperature.