印度洋海温变化与华北夏季降水减少的关系

Relationship between the Indian Ocean SST Change and Summer Precipitation Reduction in North China

使用华北地区降水资料、NCEP/NCAR再分析资料和NOAA重构的海温资料,研究印度洋海温变化与华北夏季降水减少的关系。结果表明,上年热带印度洋海温升高会造成下年华北夏季降水减少,而热带太平洋海温升高会使下年华北夏季降水增多,两者的影响相反。当年热带印度洋海温升高、热带太平洋海温升高都会造成华北夏季降水减少,两者的影响起互相加强的作用。前期热带印度洋海温变化对华北夏季降水的影响比太平洋海温变化重要。热带印度洋海温整体升高是通过东亚冬季风减弱,东亚冬季降水增加,进而影响春、夏海陆热力对比,使东亚夏季出现明显北风异常,水汽来源不足和动力辐合条件减弱,造成华北夏季降水减少。而IOD主要是通过夏季副热带高压变化来影响夏季降水。近60年华北夏季降水出现减少趋势可能与热带印度洋海温升高和IOD指数升高有关,其中热带印度洋海温整体升高的影响更为重要。

Based on the precipitation data in North China, NCEP/NCAR reanalysis data and NOAA extended recon- structed sea surface temperature (SST) V3b, we investigate the relation between the Indian Ocean sea surface tempera- ture changes and reductions of summer precipitation in North China. The results show that the increase in the tropical Indian Ocean SST in the previous year will result in the reduction of summer precipitation in North China in the fol- lowing year, while the tropical Pacific Ocean SST increase will cause more summer precipitation in North China the next year, with an opposite effect. In the same year, SST increase in both the tropical Indian Ocean and in the tropical Pacific Ocean will cause the reduction of summer precipitation in North China, they have reinforcing role. Early SST change in the tropical Indian Ocean has more important impact on the summer precipitation in North China than that in Pacific Ocean. SST increase in the tropical Indian Ocean will cause the weakening of the East Asian winter monsoon, the increase of the winter-spring precipitation, then affect the summer land-sea thermal contrast, lead to northly wind anomalies in the summer of East Asia, and inadequate water vapor, decrease in summer precipitation in North China. The IOD impact on summer precipitation is mainly through the summer subtropical high changes. The decreasing trend of summer precipitation in North China in the past 60 years is due to impact of the SST and IOD index to increase in the tropical Indian Ocean, and the overall SST increase plays a more important role.