Laboratory for Climate Studies, National Climate Center, China Meteorological Administration
本文根据国家气象信息中心提供的1979～2017 年2374站气象观测资料以及NCEP/NCAR再分析资料，利用现代统计学、物理量诊断和水汽收支方程分解等方法，探讨了华南夏季降水1993-2002年年代际增多以及2003-2013年年代际减少的水汽输送特征及其与东亚夏季风环流和关键区海表温度异常的关系，并从水汽收支平衡的角度分析华南夏季降水出现两次年代际转折的成因。研究结果表明：1993-2002年华南夏季降水增多主要受南亚高压东移和西太平洋副热带高压（简称西太副高）西伸的影响，来自菲律宾及西太副高西南侧水汽输送加强，使得华南地区低层出现强的水汽辐合； 2003-2013华南夏季降水减少主要受南亚高压异常偏西和西太副高偏东的影响，来自菲律宾及西太平副高西南侧水汽输送减弱，使得华南地区低层出现水汽辐散。华南地区夏季降水两次年代际变化主要与风速变化引起的水汽输送动力散度项的异常有关，同时还受到与比湿变化引起的水汽输送热力散度项异常、及与台风等天气尺度的涡旋引起的水汽输送涡流散度项异常影响。此外，研究发现水汽输送的异常与环流和海温异常均密切相关。
Based on the daily rainfall data at 2374 stations from the China Meteorological Administration (CMA) and reanalysis data provided by the National Centers for Environmental Prediction/ National Center for Atmospheric Research (NCEP/NCAR) during 1979-2017, the characteristics of moisture transport of precipitation increasing during 1993-2002 and decreasing during 2003-2012 over South China are compared by using the modern statistics method and the physical diagnosis method. Then, the impacts of the East Asian summer monsoon circulation systems and the sea surface temperature anomalies in the key areas on these characteristics are discussed. Finally, the reason of the two decadal changes of summer precipitation in South China is explained by using moisture transport budget equation. Results show that the increase of summer precipitation during 1993-2002 in south China was mainly influenced by the eastward movement of South Asia high and westward extension of West Pacific subtropical high (WPSH), which resulted in a strengthening of the moisture transport from the Philippines and the southwest side of the WPSH and a strong convergence of moisture in the lower layer of south China .The decrease of summer precipitation during 2003-2012 in south China was mainly influenced by the westward movement of South Asia high and eastward extension of WPSH, resulting in a weakening of the moisture transport from the Philippines and the southwest side of the WPSH and a divergence of moisture in the lower layer of south China. The interdecadal variation of summer precipitation in south China is mainly related to the anomaly of dynamic divergence of moisture transport caused by the change of wind speed, it is also affected by the anomaly of thermodynamic divergence of moisture transport caused by the change of specific humidity and the anomaly of subseasonal-scale eddies caused by typhoon and other synoptic scale eddies. In addition, we found that the moisture transport anomalies were closely related to the circulation and SST anomalies.