华南6月降水异常及其与东亚—太平洋遥相关的关系

利用1959～2010年共52年的大气环流和降水资料,我们分析了华南前汛期季风降水 (6月降水) 的变化特征,发现6月华南降水与同期EAP (East Asia-Pacific,东亚—太平洋) 遥相关型有显著的相关关系,两者之间的相关系数为0.35.EAP指数为正时,长江中下游以南的地区降水偏多,而长江以北和黄河之间的地区降水偏少.将华南6月降水分为与EAP相关的降水序列和与EAP独立的降水序列,比较了二者所对应环流异常的异同点.结果表明,与EAP相关的降水异常对应着EAP相关型的环流异常分布特征,降水为正异常时,850hPa风场从低纬度到高纬度呈现“反气旋、气旋、反气旋”的异常分布,湿的偏南风和干的偏北风在华南上空交汇,降水增多;而整个淮河流域上空为偏北风异常,导致南风带来的水汽输送减少,降水偏少,因此降水异常呈现偶极子分布.相比之下,与EAP独立的降水正异常对应的环流异常表现为热带西北太平洋上空的反气旋性环流异常,华南地区上空为显著的西南风异常,输送到华南地区的水汽增多,导致降水偏多.

Variation of South China Rainfall in June and Its Association with the East Asia-Pacific Teleconnection

Based on the atmospheric circulation and rainfall data from 1959 to 2010, the variations of summer monsoon rainfall in the pre-rainy season in South China, i.e., rainfall in June, are analyzed in this study. The results show that the South China rainfall anomaly in June is significantly related to the East Asia-Pacific (EAP) teleconnection pattern with a correlation coefficient of 0.35. When the EAP index is positive, above-normal rainfall occurs over the areas south of the middle and lower reaches of the Yangtze River, and below-normal rainfall occurs over the areas between the Yangtze River and the Yellow River. Furthermore, the South China rainfall in June is divided into two time series: one is dependent on the EAP pattern and the other is independent of the EAP pattern. Comparisons between the two corresponding atmospheric circulation anomalies are followed up. The atmospheric circulation anomalies corresponding to rainfall time series dependent on the EAP pattern are similar to the distributions of EAP related circulation anomalies. When the EAP rainfall is above-normal, there is a combination of anti-cyclonic, cyclonic, and anti-cyclonic anomalies from low latitudes to high latitudes over the tropical western North Pacific and East Asia in the lower troposphere. The southerly and northerly anomalies meet over South China, leading to above-normal rainfall there. Meanwhile, the Huaihe River basin is occupied by northerly anomalies, resulting in below-normal rainfall. By contrast, the atmospheric anomalies corresponding to the above-normal rainfall time series that is independent of the EAP pattern are characterized by an obvious anti-cyclonic anomaly over the tropical western North Pacific and southwesterly anomalies over South China, which favor water vapor transportation and resultant above-normal rainfall.