青藏高原东南侧春雨气候特征及其成因研究

The precipitation in spring may have an important impact on the onset of East Asian summer monsoon. The researches on such a field have been paid more and more attention. The Southeast Side of Tibetan Plateau is the earliest center where the spring precipitation occurs in East Asian, and the rainfall amount is very considerable and sometimes beyond that of in summer. And meanwhile the Southeast Side of Tibetan is also the earliest center where the terrestrial heat source is spurred by the release of latent precipitation heat. The Southeast Side of Tibetan in spring is probably the key climatic zone which may affect season reversal and Onset of East Asian summer monsoon. At present, it is lack about a systematic research on the climatological aspects of the spring persistent rains beside the Southeast of Tibetan Plateau. Moreover, much less researches on the cause of its formation.. This project will, through statistical and diagnostic analysis, carry out a systematic research on the climatological aspects of spring persistent rains on the southeast side of Tibetan Plateau and the cause of its formation, based on the data of rainfall and other multiple-elements analyzed of over 50 years. The project will then reveal the spatial change features of spring persistent rains on the southeast side of Tibetan Plateau, understand the impacts of such factors, for example transfer of water vapor, atmospheric circulation, MJO, area process heat and sea-land thermal contrast etc., and obtain the physical and viable pictures and the formation causes of the spring persistent rains on the southeast side of Tibetan Plateau, and reveal the impacts of regional latent heat of condensation on the formation of terrestrial heat sources before the East Asian summer monsoon established. The project can not only boost the studying of climate especially precipitation on Tibetan Plateau and its surrounding areas, but also provide an important clue for the studying of the breaking out East Asian summer monsoon.

春季降水可能对东亚夏季风爆发有重要影响，其研究越来越被关注。青藏高原东南侧春季出现东亚最早的降水中心，其降水量相当可观，有时甚至超过夏季雨量。降水的潜热释放还促使陆地热源中心最早出现在青藏高原东南侧。春季青藏高原东南侧可能是季节转换和影响季风爆发的前期气候关键区。目前青藏高原东南侧春雨尚缺乏系统的气候特征研究，成因研究则更少。项目拟利用近50年雨量资料和多要素再分析资料，通过统计分析、诊断分析系统研究青藏高原东南侧春雨的气候特征及其成因，揭示青藏高原东南侧春雨的时空变化特征，认识水汽输送、大气环流、热带印度洋MJO、区域加热、海-陆热力差异等因子对青藏高原东南侧春雨的影响，获得青藏高原东南侧春雨形成变化的物理图景和综合成因。项目不仅有助于丰富对青藏高原周边地区气候的认识，尤其是对降水的认识，还可以为东亚夏季风的爆发（建立）研究提供重要线索。

项目研究工作严格按照项目计划进行，基本完成了研究内容和目标。利用台站降水、再分析降水和大气环流资料，利用多种数理统计和物理量诊断分析方法，分析了青藏高原东南侧春雨的气候特征及其成因。研究显示：青藏高原东南侧春雨区是以贡山-察隅为中心的藏东南南部到滇西北怒江州北部，以及印度东北部阿萨姆邦和缅甸北部的部分地区。青藏高原东南侧在第8候前后，降水开始迅速增大，第16候—17候前后达到春雨峰值，在25候前后达到春雨峰值后的最低值,春雨季结束。春雨区降水具有雨季开始早于东亚其他地区,雨季持续时间长,降水年变化呈现双峰或三峰型等异于东亚其他地区的特征。青藏高原东南侧春雨年际变化明显，年代际变化不明显。青藏高原东南侧春雨典型多雨年主要表现为全区的降水偏多，尤其是横断山脉附近；少雨年表现为降水偏少，分布偏西。多/少雨年南支西风偏强/弱，在青藏高原南侧控制范围偏大/小，同期南支槽偏深/浅与偏强/弱，以及低频振荡强/弱。青藏高原东南侧的春雨区全年都是大气可降水量的高值区。春季西南水汽通道是我国及东亚地区输送水汽的最主要通道。大气中低层的偏西气流与喜马拉雅山脉—横断山脉组合导致的地形辐合是青藏高原东南侧春雨形成的直接成因。青藏高原大地形绕流作用和海陆热力差异也有辅助作用。研究工作获得了一些对青藏高原东南侧春雨新发现和认识，从以往局地性的怒江“桃花汛”分析升级到区域性（包含境内与境外）季节典型降水分析上，丰富和深化了青藏高原东南侧大气环流与降水气候的认识。