中国西北地区1961—2009年极端高温事件的演变特征

利用中国西北地区135个测站1961—2009年历年逐日地面最高气温和NCEP/NCAR资料,采用线性趋势分析、Mann-Kendall、子波分析、合成分析等方法,分析了近49 a西北地区高温事件的演变特征。结果表明:西北地区极端高温的高值区在新疆大部分地区、河西走廊西部、甘肃中北部、陇东南、宁夏北部和陕西,这些地方的高温阈值在30 ℃以上;区域年极端高温频率以1.8 d/10 a的速率显著增多,1970年代中期高温日数发生由少至多的转型,1994年有突变,高温频数有显著的3~5 a周期,目前仍处于高温频发阶段;极端最高气温介于22.5~47.8 ℃之间,最大值出现在吐鲁番盆地。4—10月皆可出现高温,但主要出现在6—8月,其中7月最多。6月高温频率增加最显著,其他月份增加不明显;高温越强,持续日数越长,高温频发的时段也是高温最强的时段。气候变暖导致极端高温事件增多,强度增强。从大气环流合成分析表明,乌山脊、巴尔喀什湖低槽和蒙古脊中高层位置稳定,大气为准正压状态,西北地区在蒙古高脊控制下,有利于形成大范围持续性高温天气。

Evolution Characteristics of the Extreme High Temperature Event in Northwest China from 1961 to 2009

Using over years daily surface extreme air temperature and NCEP/NCAR data of 135 meteorological observation stations in Northwest China from 1961 to 2009,and adopting the methods of linear regression analysis,Mann-Kendall,moving t-examination,wavelet analysis,power spectrum and composite analysis,we analyzed the evolution characteristics of high temperature event in recent 49 years of Northwest China.The results show that spatial distribution of the extreme high temperature in Northwest China presents high value in the western and eastern parts,and low value in the central part.The main areas with extreme high temperature value are located in most part of Xinjiang,the western Hexi Corridor,the central and northern Gansu,southeastern Gansu,northern Ningxia and Shaanxi.The threshold values of the extreme high temperature in these areas are above 30 ℃;but in most part of southern Xinjiang and local areas of southern Shaanxi(Xi’an,Ankang),the threshold values are above 35 ℃,the max-value is 41.5 ℃in Turpan.The annual extreme high temperature is generally low in Qinghai Plateau,and high in Qaidam Basin(25-30 ℃),the other areas are between 15 ℃ and 20 ℃,the min-value is 14.4 ℃in Wudaoliang;the frequency of annual extreme high temperature has obviously increased at a rate of approximately 1.8 d/10 a.The high temperature days changed from less to more in the metaphase of the 1970s,especially the increasing rate is 5.4 d/10 a from the end of the 1980s,and there is an abrupt change phenomenon in 1994.The high temperature frequency has the remarkable periods of 3 to 5 years in recent 49 years.At present,it is still in the frequent phase of high temperature occurence;the annual extreme high temperature becomes more and more frequent in the majority areas of Northwest China.The main significant areas with SE-NW trend are distributed in two banded regions.One is from the Qinghai Plateau to West Tianshan,another from northern Shaanxi,southeastern Gansu-Gansu Corridor to Xinjiang’s Altay.These areas tendency rate is above 2 d/10 a.The high value zone which reached above 5 d/10 a at west Hexi and the Xinjiang-Qinghai’s southern border area.This shows that in the background of global warming,extreme high temperature event occurrence is more frequent in Northwest China;the values of the extreme high temperature are between 22.5 and 47.8 ℃,the maximum value appears in the Turpan Basin,and minimum value appears in Qinshui River of Qinghai Plateau,the high temperature that above 35 ℃appears in addition to the Yili Valley of most part of Xinjiang,Qaidam Basin,Hexi Corridor,central-northern of Gansu,southeastern Gansu,Ningxia,Shaanxi,and in southern Xinjiang,the high temperature is above 40 ℃;due to influence of altitude the extreme high temperature is obviously low in Qinghai Plateau,the values of most areas are between 25 ℃and 30 ℃,dropped from north to south.The high temperature may appear from April to October,and from June to August it accounted for 93% of the whole year;the frequency of high temperature increases obviously in June and July,and the rest of months is not obvious. There is an opposite geographic distribution between high temperature intensity and the extreme high temperature,namely the areas of the extreme high temperature is accompanied with lower high temperature intensity,so is the distribution of variance of the extreme high temperature.It shows that extreme high temperature interannual changes is smaller in high-heat area.There is most closely relation between annual extreme high temperature and annual high frequency,followed by July,June and August.Therefore,the stronger of high temperature,the more continued days.From the interdecadal change,the high temperature frequent occurrence phase is also the phase of the strongest high temperature,the global warming makes the extreme high temperature events increased and the intensity enhanced.The atmospheric circulation composite analysis indicated that it is beneficial to form the wide range and long-enduring high temperature weather in Northwest China when the Ural Mountain high ridge,the low trough of Balkhash Lake and the Mongolian high ridge are stable,and the atmosphere is at the quasi-barotropic state.