黄淮和江淮地区2001年9～10月异常干旱的水汽分析

A ANALYSIS ON VAPOR OF DROUGHT EVENT BETWEEN LOWER REACHES AREA OF YELLOW RIVER AND OF YAGTZE RIVER IN SEPTEMBER AND OCTOBER 2001

文中利用NCEP/NCAR 2 0 0 1年 9～ 10月的全球日平均资料和中央气象台的逐日 0 8时 2 4h降水资料 ,着重分析了 2 0 0 1年秋季黄淮、江淮地区持续干旱时期的水汽收支及动力条件。结果表明 ,2 0 0 1年 9～ 10月该地区大气水汽含量比常年同期明显偏小 ,水汽以支出为主 ,并且南边界的水汽输出与多雨时期的情况截然不同 ;与之相反 ,有两支水汽通道将大量水汽输送到中国华西地区 ,为该地区提供了丰富的水汽。在此期间 ,江淮、黄淮地区大气层结稳定或成中性 ,对流弱 ,基本为下沉气流控制 ,使得该地区缺乏有利的动力条件 ,无法形成降水。通过分析发现 ,造成 2 0 0 1年秋季江淮、黄淮地区持续干旱时期水汽和动力条件异常的主要原因是亚洲中高纬地区盛行纬向环流 ,西风锋区位于 5 5°N附近 ,比常年同期偏北约 5个纬距 ;西北太平洋副热带高压持续偏西偏北 ,是近 2 6年来同期副热带高压脊线位置持续在 2 5°N以北时间最长的一年 ;同时 ,2 0 0 1年 9月份东亚 -西太平洋低纬度地区大气活动异于常年 ,吕宋岛附近维持一个强盛的对流中心 ,这在历史上是少有的。

Based on the NCEP/NCAR daily mean data and precipitation data from NMC, the vapor budget and dynamical condition between lower reaches area of Yellow River and of Yangtze River were analyzed during drought period of Sep.-Oct.2001. The results show that precipitable water and vapor amount in atmosphere are less than climatologic value remarkably, vapor loss mainly by outgoing from south boundary in target region. Contrarily, a great deal vapor was transported to western China by two channels. Synchronously, atmosphere was stable which caused weak convection and controlled by downdraft airflow, so there is no favorable dynamical condition for raining. Additionally, it shows that mainly causes that lead to the persisting drought event were prevailing zonal circulation in Asia high-mid latitude, westerly jet locate at 55°N, about 5 degree north to the average; the position of subtropical high consistently located to the west and north than average, it was the most persist one of recent 26-years that the High ridge position locate to such north. Tropic atmosphere activity were different from well-balanced year, a strong convective center was existing near Luzon islands in Sep. 2001 which was also unusual.