南疆夏季高温干旱时空变化特征及环流异常形势分析

Spatio-temporal features of high temperature and drought in southern Xinjiang in summer and its anomalous circulation patterns

采用1951～2007年南疆地区气温站点资料和NCAR/NCEP气候月平均资料,运用二项式系数加权平均法、Morlet小波变换等方法分析了南疆地区夏季气温异常的时空变化特征,并对异常年份环流形势进行了合成分析。结论如下:57年之中南疆夏季气温异常的频率达26%。气温异常存在显著周期为20年周期震荡,和弱的10年周期震荡。不同的年代气温异常的分布各不相同,但从气温长期演变趋势来看南疆北部(天山山脉南侧)主要为气温升高的趋势,塔里木盆地以及南疆南部地区主要为气温降低趋势,吐鲁番盆地附近处于升温中心。南疆夏季酷暑年和凉夏年的环流形势基本相反。酷暑年中高纬乌拉尔山到鄂霍次克海附近500hPa高度场异常偏低,我国东北到东北亚地区上空高度场异常偏高,低纬度南亚地区上空高度场异常偏低,这几个地区的高度场变化是影响南疆地区夏季高温干旱的关键因素。我国中纬度地区上空200hPa急流显著加强,南疆地区位于急流增强中心的西侧,非地转风正涡度加大。低空850hPa气流在贝加尔湖附近辐合加强,印度洋存在两处较强的反气旋式距平环流,低空风是否能将对印度洋暖湿气流输送到南疆地区是该地夏季气温和干燥程度的重要因素。OLR场异常特征对南疆夏季高温干旱有较好的指示意义。

With binomial coefficient smooth,Morlet wavelet analysis,the temperature anomalies Spatio-temporal-varying characteristics change and its anormalous circulation patterns were analyzed with the observed data of air temperature at stations in Southern Xinjiang from 1951 to 2007 and NCAR/NCEP monthly mean data.Results showed that the frequency of southern Xinjiang temperature anomalies was 26% in summer during the last 57 years.The summer temperature anomaly showed the 20-year inter-dewcadal periodic variations and a quasi-ten year inter-annual periodic variations.Distribution of abnormal temperature varied with different decades.However,according to long-term trend of air temperature,north of Southern Xinjiang（Southern Tianshan Mountain）became hotter,while Tarim basin and south of Southern Xinjiang became cooler,Turpan neared the warming center.The circulation patterns contrasted sharply in hot summer and in cool summer.In hot summer years,500 hPa height became exceptionally low from the Urals to the Okhotsk regions,exceptionally high from Northeast China to Northeast Asia,and exceptionally low in the low latitude area.Therefore,the height changes of these regions were the key factors of the high temperature and drought in Southern Xinjiang.200 hPa jet stream over China＇s mid-latitudes significantly strengthened,Southern Xinjiang is at the west side of enhancing center,where plus ageostrophic vorticity increased.Flow convergence on the 850 hPa enhanced near Baikal,and two strong anti-cyclonic anomalies circulation appeared over the Indian Ocean.Low-level wind transporting warm and wet flow over the Indian Ocean to Southern Xinjiang determined the summer temperature and drought anomalies.OLR anomalies field had a better indication for the summer high temperature and drought in southern Xinjiang.