采用西南120站逐月夏季降水, 美国CPC年逐月Ni?o3.4指数, NCEP/NCAR逐月环流等资料, 分析了ENSO事件的季节演变对西南夏季降水的影响及其机制。结果表明, ENSO事件衰减对西南降水有重要影响, 这种影响主要由赤道中东太平洋海温影响菲律宾对流活动进而持续调制西太平洋副热带高压(简称西太副高)实现, 与ENSO事件的结束季节有重要关联。在El Ni?o（La Ni?a）衰减年, 随着事件结束时间从冬季向春、 夏季推迟, 赤道中东太平洋海温释放能量增大（减弱）, 西太副高向大强西南（小弱东北）的方向发展, 加强（抑制）南海的水汽输送, 影响着孟加拉湾水汽输送, 从而影响西南降水异常分布, 其显著区域随着事件结束季节的推迟而扩大, 在El Ni?o衰减次年更为突出。依据能量累积释放效应, 从前一年9月开始的逐月Ni?o3.4区累积海温能更好指示夏季西太副高的强弱和大小, 当4 -5月的累积海温超过±0.5时, 与夏季副高面积、 强度指数的符号一致率为100%。因此, 能够依据累积海温判断夏季西太副高强弱、 大小, 从而判断西南夏季降水的异常趋势。
Based on monthly summer precipitation at 120 stations in Southwest China, monthly Ni?o3.4 indices from CPC, monthly circulation data from NCEP/NCAR and other meteorological data, the influence of ENSO event evolution on summer precipitation in southwest China and its mechanism are analyzed in this paper.As the results shown, the attenuation of ENSO events has an important effect on Precipitation in Southwest China.This effect closely relates to the end season of ENSO events and mainly due to the influence of SST in the equatorial Middle East Pacific on Philippine convective activities, which continuously modulate the West Pacific Subtropical High (WPSH).In El Ni?o (La Ni?o) decay years, the WPSH develops stronger and more southwest (weaker and more northeast) due to more (less) energy releases in the equatorial Middle East Pacific Ocean.That strengthens (restrains) the transport of water vapor from the South China Sea, and affects the water vapor transportation from the Bay of Bengal and then affects the anomalous distribution of precipitation in southwest China.Moreover, this influence is significant in more area of Southwest China with the delay of the end season of ENSO events, especially in El Ni?o decay years.For the cumulative release effect of energy, the monthly cumulative SST in the zone of Ni?o3.4 from pre-September is better to indicate the change of the summer WPSH than monthly SST.When the accumulated SST in April and May exceeds (±0.5), its sign consistency rate with the area and intensity index of summer WPSH is 100%.Thus, the summer abnormal precipitation in Southwest China could be judged from the intensity and magnitude of WPSH which could be forecasted with the accumulated SST.
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