乌鲁木齐地区夏季气象干旱的变化特征及成因分析

为了更准确的掌握乌鲁木齐地区夏季气象干旱的变化特征并研究其成因，以乌鲁木齐地区5个站点的历史降水资料为基础，统计得到其1961-2015年夏季累积降水在100～250 mm范围内变化，并通过计算Z指数来表征干旱变化特征，利用Mann-Kendall检验和Morlet小波分析归纳了乌鲁木齐夏季气象干旱在1980年代中期的突变特征以及1986年以来12 a左右的周期性变化特征。在此基础上结合NCEP/NCAR再分析资料、JRA海表温度（SST）等数据，通过对比典型旱/涝年的异常特征，对夏季气象干旱发生的成因进行了分析，发现低纬东风输送强时水汽可由80°～90°E向北越过青藏高原影响新疆地区，反之则包括乌鲁木齐在内的天山以北地区可降水量都偏少，并且指出赤道东太平洋SST异常所导致的赤道纬向垂直环流异常是导致这一差异的可能成因。此外还对乌鲁木齐夏季气象干旱与大气环流指数存在的关联进行了讨论。这些结果为乌鲁木齐降水机理研究以及气候预报提供了重要依据，并为人工影响天气和抗旱减灾工作提供了有力支撑。

Characteristics and causes of meteorological drought in summer in Urumqi

Urumqi area is an important political,economic and cultural center in the Xinjiang Uygur Autonomous Region and northwest China,it is also an inland area threaten by drought.In order to better understand the characteristics of meteorological drought in Urumqi area in summer and study its causes,historical precipitation data from 5 stations in Urumqi area from 1961 to 2015 were utilized,and the statistical result shows that the accumulated precipitation in summer kept changing in the range between 100 mm to 250 mm. Then,Z index was calculated to show the variation characteristics of meteorological drought,and an abrupt change point in mid 1980s and a periodicity change of about 12 years were found by using Mann-Kendall test and Morlet wavelet analysis.Based on this,using NCEP/NCAR re-analysis data and JRA sea surface temperature (SST) data,the causes of drought in summer was studied by comparing the anomalies of relevant meteorological variable fields in drought years and flood years. It is found that water vapor can pass over the Qinghai Tibet Plateau from south to the north at 80~90°E and affect Xinjiang area when the east wind at low latitude West Pacific is strong,otherwise there will be less precipitable water in the northern part of Tianshan Mountains in Xinjiang including Urumqi area. It is also found that the anomalies of vertical zonal circulation of equator caused by SST anomalies in equatorial eastern Pacific is the possible cause of these differences.In addition,the relationship between meteorological drought and 74 atmospheric circulation index in summer in Urumqi is also discussed,and 10 indexes in early season show significant correlations with the drought variation in Urumqi.These results can help to improve the climate forecast and support the weather modification,drought resistance and disaster reduction work.