6月长江中下游降水和春季东亚季风区土壤湿度的关系

The relationship between June precipitation over mid-lower reaches of the Yangtze River basin and spring soil moisture over the East Asian monsoon region.

  • 摘要: 利用美国气候预测中心(CPC)土壤湿度资料、中国台站观测降水资料以及NCEP/NCAR再分析的风场和气温资料,在去除了降水资料中的ENSO信号的影响后,分析了6月长江中下游降水和春季东亚季风区土壤湿度的关系。结果表明,长江中下游6月降水和前期春季土壤湿度存在很显著的正相关关系。进一步分析表明,当中晚春(4—5月)长江中下游地区的土壤湿度偏高(低)时,晚春(5月)长江中下游上空低层气温偏低(高),从而导致东亚季风区的海陆温差减小(增加)。海陆温差的减弱(增强)使得6月东亚夏季风较常年偏弱(强),伴随的风场异常主要体现在长江以南地区为南风(北风)异常所控制,而长江以北则为北风(南风)异常,从而使得长江中下游存在着异常辐合(散),最终导致长江中下游降水量较常年偏多(少)。

     

    Abstract: Using the US Climate Prediction Center (CPC) soil moisture dataset and the observed precipitation over China together with the NCEP/NCAR reanalysis wind and air temperature, the relationship between June precipitation over mid-lower reaches of the Yangtze River basin (MLR-YRB) and spring soil moisture over the East Asian monsoon region was explored, with the signal of the ENSO effect on precipitation removed. A significant positive correlation was found between the mean June precipitation and the preceding soil moisture over the MLR-YRB. The possible response mechanism for this relationship was also investigated. It is found that when the soil over the MLR-YRB is wetter (drier) than normal in April and May, the air temperature in the lower troposphere over this region in May is lower (higher) than normal, and this temperature effect leads to a decrease (increase) in the temperature contrast between the land and the sea. Generally, a decrease (increase) in the land-sea temperature contrast leads to weaker (stronger) East Asian summer monsoon in June. Southerly (northerly) wind anomalies at 850 hPa then show up in the south of the Yangtze River basin while northerly (southerly) wind anomalies dominate in the north. These anomalies lead to the convergence (divergence) of wind and water vapor and hence gives rise to more (less) precipitation in June over the MLR-YRB.

     

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