2011年春季河南久旱转暴雨的环流特征及成因分析

利用常规气象观测资料、NCEP/NCAR 1°×1°和2.5°×2.5°全球再分析资料,对2011年5月河南久旱转暴雨过程的影响系统及环流演变特征进行分析。结果表明,暴雨产生在高空槽前、中低层切变线南侧、低空急流出口左侧强的低空辐合区。将干旱期间与暴雨时段大尺度环流场进行对比分析得出,干旱期间500 hPa高度场长期维持＂西高东低＂的环流形势,暴雨时段环流迅速调整为＂东高西低＂,上游也由干旱时期的高度正距平转为负距平,下游由高度负距平转为正距平。干旱期间西风急流和南亚高压主体均较偏南,暴雨时段二者均快速加强北移,暴雨区恰好位于二者交汇的高空强辐散区。干旱期间AO指数及NAO指数均为正值,当二者先后由正值转为负值时,有可能预示着后面将有强降水发生。

Circulation Characteristics and Genetic Analysis from Long-term Drought to Rainstorm in Spring 2011 of Henan

By using the conventional meteorological data, NCEP/NCAR 1°×1° and 2.5°×2.5° global reanalysis data, the influence systems and circulation evolution characteristics from long-term drought to rainstorm in May 2011 of Henan were analyzed. The results show that the rainstorm generated in a strong low-level convergence zone where it is in front of the upper trough, the south side of the low- level shear line and the left side of the export of low-level jet. Comparing and analyzing the large-scale circulation field during periods of drought and rainstorm, we found that the 500 hPa height field main- tained a long-term ＂west higher and east lower＂ circulation pattern during the drought period but the cir- culation adjusted to ＂east higher and west lower＂ quickly during the rainstorm period. The height anoma- lies and negative anomalies interchanged from drought period to rainstorm period both in upstream and downstream. The westerly jet and the main body of South Asia high were in the south during period of drought but they both moved to the north rapidly during the rainstorm period, and the rainstorm areas were just at the strong high-ahitude divergence areas where they joined each other. AO index and the NAO index were positive during period of drought. When they are negative value from positive value suc- cessively, it may indicate the rainstorm will occur later.