2009／2010年西南地区秋冬春持续干旱的成因分析

Causative Analysis of Continuous Drought in Southwest China from Autumn 2009 to Spring 2010

利用国家气候中心提供的1951—2010年逐日综合气象干旱指数(CI)和大气环流监测指数,结合西南地区335个站的逐日降水资料、逐日NCEP/NCAR再分析资料、NOAA提供的逐日OLR资料,通过REOF提取干旱空间分布型,采用合成分析和相关分析等方法,从西太平洋副热带高压、印缅槽、对流活动、水汽输送及垂直运动等几个方面,揭示了2009/2010年西南地区秋冬春持续干旱的大气环流异常特征。研究发现此次极端干旱事件发生在中等强度中部型l Nino背景下,受其影响,反Walker环流导致赤道120°E附近形成显著异常的下沉运动,菲律宾周边地区存在一个强大的异常反气旋,同时,西南地区受异常西北气流控制,两者的共同作用,使对流层低层存在明显气流辐散区,其持续异常是极端干旱发生的重要原因。

Based on the 1951-2010 daily Compound Index （CI） and atmospheric circulation monitoring in- dex provided by National Climate Center, the daily precipitation data of the 335 stations in the Southwest China, the daily NCEP/NCAR reanalysis data and the daily OLR data of NOAA, the distribution of the drought patterns in the Southwest China was analyzed by using the REOF method, and the characteristics of atmospheric circulation anomalies such as western Pacific subtropical high （WPSH）, Indian-Burma trough, convection activities, water vapor transportation, and vertical motion of the continued drought from autumn 2009 to spring 2010 in the Southwest China were revealed according to the composite analysis and correlation analysis methods. It was found that the extreme drought occurred in the medium strength and central pattern E1 Nino background, instead of statistical typical La Nifia background. The results in- dicated that influenced by the central type E1 Nifio, the anti-Walker circulation caused the significantly ab- normal sinking movement around 120°E in the equator and a strong abnormal anti-cyclone in the South Chi- na Sea and the surrounding areas of Southeast Asia. At the same time, the Southwest China was affected by the abnormal northwest air stream. By both influences, an obvious airflow divergence area occurred in the lower troposphere and its persistence was the key cause for the extreme drought.