青藏高原东南侧南风演变特征及其与中国东部春季降水的关系分析

Characteristics of South Wind in East Southern Tibetan Plateau and Its Relationship with Eastern China Spring Rain

使用1979—2008年NCEP/NCAR再分析数据集资料分析了全年各月经向风特征,发现青藏高原东南侧存在一个全年盛行南风的区域(22.5°～30°N、105°～110°E),即常年南风区。该区域南风呈现冬弱夏强的演变特征,尤其在春夏时期呈现双峰值状态,峰值分别出现在15候和37候左右。进一步分析表明,常年南风区南风与我国南方春季降水有着较好的对应关系。15候左右常年南风区南风第一次增强并达到峰值,持续的强南风使得我国南方地区降水随之有突然增加的趋势,进入春雨期。高原东南侧常年南风区南风两个峰值出现的原因并不相同。15候左右出现的绕流南风大值是由于高原的突然加热产生的低空气旋性环流叠加在绕流西风上,从而造成了南风的加强,湿润的偏南风给华南地区带来持续的降水,江南春雨开始。而37候左右出现的绕流南风大值是由于南海夏季风爆发后,孟加拉湾槽前强大的西南风加强了该处的绕流南风,使得南风势力变得更为强大,推进到我国长江中下游地区。

Abstract： Utilizing the NCEP/NCAR reanalysis data, the characteristics of annual south wind over East Asia are investigated. And it is discovered that a key area （22.5^--30~N, 105^- ll0~E） where the south wind prevails all the year is over the southeast of the Tibetan Plateau. The south wind is strong in summer and weak in winter, showing a double peak. A peak occurs in the 15th pentad and the other peak occurs in the 37th pentad. Further research found that there is a good relationship between the south wind on the southeast of Tibetan Plateau and the spring precipitation in southern China. In the 15th pentad, the south wind on the southeast of Tibetan Plateau becomes stronger and expands eastwardly, and then the rainfall in the south of China becomes heavy. The occurring reason for the two peaks of the south wind is different. The south wind peak occurring in the 15th pentad is for a low-level cyclone caused by the Tibetan Plateau heating superimposed over the south wind. It causes the south wind stronger, and then South China comes into rainy period. The south wind peak occurring in the 37th pentad is while the South China Sea monsoon broke out, the southwest wind in front of the Bay of Bengal trough intensifies the south wind. And then it brings about the rain over the Yangtze River.