用水汽输送表征的东亚副热带夏季风指数研究

AN EAST ASIAN SUB-TROPIC SUMMER MONSOON INDEX DEFINED BY MOISTURE TRANSPORT

利用1971～2000年NCEP/NCAR逐日再分析资料及同期中国站点降水资料,在讨论水汽输送的气候特征及逐候演变的基础上,用整层积分的经向水汽输送定义了一个副热带夏季风指数。研究结果表明,对110～120°E纬向平均的水汽输送通量而言,其逐候演变可反映出东亚夏季风的进退过程。定义的水汽输送指数可表征夏季风的异常变化特征,高(低)指数年对应的副热带季风偏强(弱);该指数与长江中下游夏季降水存在高度的同期正相关,高(低)指数对长江中下游夏季降水的多(少)有较强的分辨能力。此外,来自西太平洋经南海北上的水汽与北方冷空气在长江中下游的辐合很可能是造成长江中下游异常降水偏多的原因。

Using daily NCEP/NCAR reanalysis dataset and observation rainfall data in China for the 1971 - 2000 period, a sub-tropical summer monsoon index is defined by meridional moisture transport of the total atmosphere based on the discussion about climate characteristics of moisture transport. Results show that the advance and retreat of east Asia summer monsoon can be reflected by the intraseasonal variation of moisture transport averaged over 110- 120 °E. The sub-tropical summer monsoon index defined by difference of meridional moisture transport between South China and North China can be used to describe the intensity of the subtropical summer monsoon. High（low） index is corresponding to strong（weak） sub-tropical summer monsoon. And the new index is well related to the summer rainfall over the middle and lower reaches of the Yangtze River. In addition, the convergence of moisture transport from the west Pacific via the South China Sea and that from the North China may be responsible for the anomalously excessive summer rainfall over the middle and lower reaches of the Yangtze River.