中文摘要：

通过对观测资料的诊断分析,发现青藏高原（下称高原）东南侧存在一个常年南风区,无论是气候平均场还是年际变化的主要模态,该地区均表现为常年经向风分量维持南风,这与东亚典型的季风气候是矛盾的;然而,它同时具有显著的季节变化特征,早在2月就出现了季节性的南风增强,是东亚地区大气环流形势由冬转夏的＂敏感区＂;并且在3月底4月初及6月底分别达到峰值,形成＂双峰＂结构,恰为东亚副热带夏季风的开始建立时间和盛期阶段,因此,高原东南侧常年南风区南风与东亚副热带夏季风密切相关。不仅如此,常年南风区南风偏强年,夏季6～8月我国东部地区盛行偏强的西南风,雨带推进至更北的地区,西太平洋副热带高压偏强偏西,然而越赤道气流偏弱,孟加拉湾槽偏弱,表明此时热带夏季风偏弱。在常年南风区南风偏强年,热带夏季风偏弱,东亚副热带夏季风偏强,正是由于东亚副热带夏季风异常偏强,偏南风向北推进至华北-东北。因此,高原东南侧常年南风区南风既有特殊性又有重要性,是影响我国东部天气气候事件的关键区域。

英文摘要：

Observations indicate that there is a special region on the southeast side of Tibetan Plateau,over which the meridional wind is always the southerly during the whole year both in the climatology or the EOF domain mode.This is different from the typical East Asia monsoon climate.However,the southerly has significant seasonal variation.As early as in February it has seasonal enhancement in southerly phase,which demonstrates this special region is sensitive to the East Asia general circulation transition from winter to summer.Moreover,in later March to early April it reaches its peak,forming double-peak structure.These two time points are just when the East Asian subtropical summer monsoon onsets and becomes matures.Consequently,the southerly is closely related with the East Asian subtropical summer monsoon.Furthermore,in the strong southerly year,intense southwesterly wind prevails in eastern China in summer（JJA）,which brings the rain belt to much northward,the west Pacific subtropical high is much stronger and locates more westward than usual.However,at the same time the crossing-equator flow is weak and the trough over Bay of Bengal is of weakness.These indicate that the tropical summer monsoon is weaker than normal.That is,in strong southerly year the East Asian subtropical summer monsoon is more intense while the tropical summer monsoon is weaker than normal.Therefore,the southerly wind over the southeast Tibetan Plateau is special and important,where is the key region for the weather and climate in eastern China.