2010年陕西盛夏极端多雨的气候特征及成因研究

利用NCEP/NCAR再分析资料,对陕西省2010年盛夏极端多雨的形成机理进行了个例分析研究。结果表明:2010年盛夏极端多雨的主要成因是大尺度环流形势异常及海温异常等多种因素综合作用的结果。在500 hPa高度场上欧亚中高纬区为"两脊一槽"型分布,乌拉尔山阻塞高压与咸海到巴尔喀什湖的低压槽稳定维持,低槽分裂冷空气沿中纬度西风带东移,与西太平洋副热带高压外围西北侧暖湿气流在陕西上空相汇,是造成2010年陕西盛夏极端多雨的直接原因。来自南海的水汽输送在850 hPa、700 hPa上表现都很显著,来自孟加拉湾的水汽只有850 hPa表现明显。La Ni?a事件当年陕西盛夏降水易偏多利于出现极端降水。盛夏降水量年代际变化特征显示,陕西中部和南部2010年处于一个年代际的多雨期内,出现极端降水的可能性增大。

Climatic Features and Cause Analysis of Extreme Rain Events in Shaanxi during the Midsummer of 2010

Based on analyzed NCEP/NCAR data, the mechanisms for extreme rain events during the midsummer of 2010 has been investigated. The results show an abnormal general circulation caused mainly by the sea surface temperature. There is a two ridges and one trough circulation pattern above mid-high latitude at 500 hPa, where the Eurasia and the Ural blocking highs and the low between the Aral Sea and Lake Balkhash were kept stable, and the small trough split from the low migrated eastwards along the westerly in mid-latitude Asia, converging with warm humid air masses from the northwest edge of the west Pacific subtropical high above Shaanxi. These factors directly resulted in extremely rainy weather during the high summer of 2010. The greater amounts of water vapor from the periphery of the Arabian Sea, the highs in the South China Sea and the western Pacific subtropics transported to Shaanxi at 850 hPa, and the formation of a strong cyclonic convergence zone in Shaanxi and its upstream region were all very conducive to the occurrence and continuation of extreme precipitation. At 700 hPa, two clear vapor conveyor belts and, upstream of Shaanxi, a generating and developing southwest vortex (the main system causing the rainstorm in Shaanxi) occurred. Decadal variations in precipitation during high summer also indicated that after 2010 Shaanxi was in a decadal period during which the possibility of extremely rainy weather was quite great. Further, during La Niña event years, the high summer in Shaanxi also favours extremely rainy weather.