北疆冬季持续性低温事件特征及大气环流异常分析

利用新疆天山山区及其以北地区（北疆）45个气象站1961-2010年冬季逐日最低气温资料，提出了45站低温日标准和区域性持续性低温事件的定义，并分析了持续性低温事件的时空分布和变化特征，研究了低温事件的年代际变化环流差异特征、大尺度环流背景、冷空气影响路径及强度特征。结果表明：(1) 低温日阈值呈东北向西南升高的分布趋势，低温日阈值最小值分布于准噶尔盆地和新疆北部阿勒泰地区，阈值为-34～-30℃，而西部伊犁地区和天山山区低温日阈值为-24～-20℃；(2) 1961-2010年出现35次大范围持续性低温事件，1月和2月发生频次均为0.29次/年，12月为0.14次/年；低温事件持续时间为5~25 d，其中超过10 d有16次，5~9 d有19次。持续性低温事件发生频率呈年际和年代际显著减少趋势，但强度无显著变化趋势；(3) 北半球大范围环流异常造成新疆持续低温事件，以经向环流异常为主，根据冷空气影响路径可分为4类：西西伯利亚横槽、中西伯利亚低槽东灌、北风带和西北风带、北脊南槽（涡），这4类冷空气影响路径表现为500 hPa冷空气从极地或西伯利亚以超极地、西北和偏东路径进入新疆后，-32℃冷空气南压位于北疆地区，海平面气压场同时表现为蒙古高压盘踞欧亚大陆，高压中心达1045 hPa以上且位于阿勒泰山地区，1035 hPa冷高压控制北疆地区，这种环流配置造成新疆持续性低温事件。

Characteristics of Persistent Low Temperature Events and Analysis of Atmospheric Circulation Anomaly in Winter in Northern Xinjiang

Based on daily minimum temperature data of 45 observation stations in winter in Tianshan Mountains and northern Xinjiang from1961 to 2010, we presented the standards of 45 stations’low temperature day and the definition of regional persistent low temperature events (PLTE), and analyzed its spatial-temporal distribution and variation, further investigated circulation anomaly features of decadal change, large-scale circulation background, affecting system and cold air features on PLTE. The results are as follows. Low temperature day thresholds were elevated distribution pattern from northeast to southwest, minimum thresholds in Junggar Basin and Altay region of northern Xinjiang, with the values of -34℃ to -30℃, -24℃ to -20℃ in the western Yili region and Tianshan Mountains. PLTE appeared 35 times in the past 50 years, the occurrence frequencies are both 0.29 times per year in January and February, 0.14 times per year in December. Low temperature events’duration ranged from 5 d to 25 d, among 16 times over 10 d, 19 times from 5 d to 9 d. PLTE showed significant interannual and decadal decreasing trend, but no significant intensity change. PLTE were caused by large-scale circulation anomalies in the Northern Hemisphere, mainly the meridional circulation anomalies. They can be divided into West Siberian transverse trough type, Central Siberia trough east infalling type, north wind belt and northwest wind belt type and the north ridge-south trough (vortex) type. When cold air from the Arctic or Siberia enters into Xinjiang by super polar, northwest, eastward paths on 500 hPa, northern Xingjiang is controlled by -32℃ cold air and ground Mongolia High dominated in the Eurasia continent, high pressure center of over 1045 hPa locating in the Altay Mountains region, 1035 hPa cold high pressure controlling northern Xinjiang region.