南亚高压和西太副高位置与中国盛夏降水异常

用全国160站降水资料及ECMWF逐月再分析资料,采用合成分析方法,讨论了年际变化尺度上南亚高压与西太副高纬向位置异常与盛夏降水的关系。结果表明,当南亚高压与西太副高纬向异常重叠(分离)时,长江中下游流域存在异常上升(下沉)运动,江南的广大地区存在异常下沉(上升)运动。且当两个高压纬向异常重叠时,来自北印度洋及西太平洋的水汽,在长江中下游流域异常辐合,降水偏多。此时,江南地区水汽通量异常辐散,降水偏少。当两个高压纬向异常分离时,水汽主要来自北印度洋的西南风输送,长江流域降水偏少,江南地区降水偏多。

South Asian high and the subtropical western Pacific high and its relation to the mid-summer precipitation anomalies over China

Based on the monthly precipitation of 160 stations in China and the ECMWF monthly reanalyses, the relationship between the longitudinal location anomalies of the South Asian high (SAH) and the Subtropical Western Pacific high (SWPH) and the mid-summer precipitation anomalies over China has been investigated by using the composite analysis. The results show that when the longitudinal location of the SAH (SWPH) moves further eastward (westward) than normal, both anticyclones (SAH and SWPH) overlap in the east-west direction on the basis of interannual variation, the anomalous ascending motion appears in the middle and lower Yangtze valley, while the anomalous descending motion occurs in the south China. The moisture from the northern Indian Ocean and South China Sea converged in the middle and lower Yangtze valley, which leads to abundant precipitation over the middle and lower Yangtze valley. As the SAH and the SWPH overlap over the south China, the abnormal moisture divergence occurs, which leads to scarce precipitation. When the SAH and the SWPH move further apart from each other than usual on the basis of interannual variation, the moisture comes mainly from the northern Indian Ocean, and anomalous ascending motion and more precipitation occur over south China. At the same time, abnormal descending motion and less precipitation occur over the middle and lower Yangtze valley.