西太平洋副热带高压对长江流域夏季降水的影响在1970s末的转变及机理

The western Pacific subtropical high greatly affects the rainfall over the Yangtze River basin (YRB) during summer. The southwestward extension of the subtropical high favors enhanced rainfall over the YRB, and vice versa. This correspondence between them is a base for the current short-term climate prediction. However, our preliminary results indicate their relationship experiences a decadal change: the relationship is weak and insignificant during 1958－1978, but becomes strong and significant during 1979－2014. Based on this phenomenon, this project will investigate the statistical characteristics of this decadal change in depth. Further, the underlying physical mechanisms would be explored by analyzing the decadal changes of the water vapor transport and the equivalent potential temperature associated with the subtropical high. The role of the change in basic state would also be identified. The results of this project would be helpful for a better understanding of the variability of the atmospheric circulation and climate over East Asia, and contribute to the improvement of the seasonal prediction of the YRB rainfall.

夏季西太平洋副热带高压显著影响长江流域降水，是目前短期气候预测的重要基础之一。然而，申请人的初步结果表明，副高与长江流域夏季降水之间的关系在1970s末发生了明显的年代际转变：1970s末之前，副高对长江流域夏季降水的影响较弱；而在此之后，副高的影响显著增强。本项目拟在此基础之上，对两者关系发生年代际转变的具体特征进行深入分析，并从副高对水汽输送、相当位温影响的年代际转变以及气候态动力、热力背景场的年代际转变与影响等角度对其中的物理机制进行探讨。项目成果将有助于加深对东亚大气环流和气候变化的认识，并为提高长江流域夏季降水的季节预测提供理论依据。

夏季西太平洋副热带高压（副高）显著地影响长江流域降水，一般来说，当副高偏西（东）时，长江流域降水增多（减少）。两者之间的对应关系是现阶段长江流域夏季降水预测的重要基础之一。目前气候模式可以较好地预测出副高的变动，为长江流域夏季降水的季节预测提供了很好的前提条件。然而，本项目的研究结果表明，副高与长江流域降水之间的关系并不是稳定的，两者的关系在1970s末发生了明显的年代际转变：1970s末之前，副高对长江流域降水的影响较弱；而在此之后，副高的影响显著增强。本项目对两者关系的年代际转变特征进行了深入分析，并从副高自身的变化和气候背景场的变化两个方面揭示了其中的物理机理，指出1970s末之后，副高自身变率的增强和热带西太平洋热力背景场的变化都有利于副高和长江流域降水关系的增强。项目成果有助于加深对东亚大气环流和气候变化的认识，并为提高长江流域夏季降水的季节预测提供理论依据。