中南半岛春季土壤湿度异常对亚洲热带夏季风建立和发展的影响

利用WRF区域模式模拟分析了中南半岛地区春季土壤湿度异常对亚洲热带夏季风建立和发展的影响,结果表明:亚洲热带夏季风对中南半岛春季土壤湿度的响应是不对称的,当中南半岛春季土壤湿度偏高时,中南半岛及孟加拉湾周边地区呈现异常东风,伴随降水减少,季风减弱;而中南半岛春季土壤湿度偏低时,孟加拉湾及周边地区西风减弱,降水减少,季风也对应减弱。通过进一步分析物理机制得到,中南半岛春季土壤湿度异常偏高使季风建立初期感热减小,陆表温度明显降低,从而导致海陆温差逐渐降低,使季风减弱;而中南半岛春季土壤湿度异常偏低使整个中南半岛区域蒸发减少,导致地表向上输送的水汽减少,减弱季风环流和降水。此外,通过分析850 h Pa纬向风及对流层中上层经向温度梯度两项季风暴发指数,探讨了中南半岛春季土壤湿度异常对孟加拉湾东部季风暴发时间的影响,结果表明:中南半岛春季土壤湿度偏高时,孟加拉湾东部季风暴发时间大约推迟10天左右,而土壤湿度较低对亚洲热带夏季风暴发时间影响甚微。

Influence of Spring Soil Moisture Anomaly in the Indo China Peninsula on the Establishment and Development of Asian Tropical Summer Monsoon

The effect of spring soil moisture anomaly in the Indo China peninsula on the establishment and development of the Asian tropical summer monsoon are studied using the WRF model. Results indicate that the responses of the Asian tropical summer monsoon on soil moisture in the Indo China peninsula are not symmetric. When the spring soil moisture is high, easterly wind anomalies appear over the peninsula and surrounding areas and local precipitation decreases, corresponding with weaker summer monsoon. On the contrary, low soil moisture is associated with weak westerly over the Bay of Bengal and surrounding areas, and decreasing precipitation, weaker summer monsoon. The physical mechanisms are also discussed. The effect of high soil moisture is mainly due to the decrease in the difference in surface temperature between land and sea. For the dry condition, the summer monsoon response may be caused by the decrease in evaporation. Besides, we also analyze the zonal wind at 850 hPa and the meridional temperature gradient to understand the impact of spring soil moisture anomalies on the timing of monsoon establishment over the east of the Bay of Bengal. High soil moistureleads to a 10 days delay in monsoon establishment, but the impact of low soil moisture is small.