北极涛动与南支槽的关系及对云南冬春季降水影响的研究

Yunnan is located in the southeast of the Qinghai-Tibet Plateau, where the precipitation in winter and spring is mainly affected by Southern Trough which is formed from westerly jet in the bay of Bengal. The active Southern Trough brings heavy precipitation (snow), thunderstorms, hail and other disastrous weather easily in Yunnan. However, the inactive Southern Trough easily leads to winter and spring drought in Yunnan. Studies show that AO not only affects the atmospheric circulation in middle and high latitude areas, but also has a significant relationship with low latitude circulation. AO can affect the atmospheric circulation in the Bay of Bengal region by the wave train of Eurasian teleconnection pattern in the Middle East jet stream. The extreme drought in Southwest China during 2009/2010 winter and spring is related to the weak Southern Trough leading by the AO negative anomalous and the Eurasian teleconnection pattern. The previous research proves that AO has a significant relationship with the precipitation in winter and spring in Yunnan, which is dissymmetric correlationship, but its mechanism is not clear. This project will use mathematical statistics and dynamic diagnosis methods to study the influence of AO mode on the Eurasian teleconnection wave eastward-propagating and the southern trough’s activity. It will also analysis the effect on the Southern Trough generation and deepening in the extreme precipitation events, and study how AO affects the precipitation in Yunnan and its formation mechanism of the asymmetric to provide the key area and precursory signal for the extreme rainfall prediction. This project will publish 4-8 papers in the core journals.

云南地处青藏高原东南侧，冬春季降水主要受西风带急流在孟加拉湾形成的南支槽影响。南支槽影响云南易出现强降水（雪）、雷暴、冰雹等灾害性天气，而南支槽不活跃易引发云南的冬春季干旱。研究表明北极涛动不仅影响中高纬地区的大气环流，与低纬度地区环流也存在显著联系。北极涛动可以通过中东急流上的欧亚遥相关波列的传播影响孟加拉湾等地区。2009/2010年冬春季西南干旱就与AO为异常负值、欧亚遥相关波列引起南支槽偏弱有关。前期研究发现AO与云南冬春季降水显著相关，并为不对称相关，但其机理并不清晰。本项目采用数理统计和物理诊断方法，研究AO模态对欧亚遥相关波列东传及南支槽活动的影响，分析极端降水过程中AO对南支槽形成和加深的作用，研究AO对云南降水的影响及不对称影响的机理，为预测预报提供关键区和前兆信号。项目将在核心期刊发表4-8篇论文。

云南地处青藏高原东南侧，冬春季降水主要受孟加拉湾南支槽影响。南支槽影响云南易出现强降水（雪）、雷暴、冰雹等灾害性天气，而南支槽不活跃易引发云南干旱。本项目研究显示，冬春季AO与云南降水存在复杂不对称关系：AO与降水正相关关系11-2月仅负位相年显著，3-4月仅正位相年显著。研究揭示北非副高和西太副高位置及形状对波列东传有重要影响，体现在副高反气旋外围气流与波列的协同作用上。AO正（负）位相时欧洲西部、乌山至里海、贝湖以东为“脊-槽-脊”（“槽-脊-槽”）的EU波列，中低纬地中海-北非、阿拉伯海、孟加拉湾为“槽-脊-槽”（“脊-槽-脊”）的南欧亚波列（SEA），形成高原“北脊南槽”形势，有（不）利于冷暖气流在云南交汇。云南强降水个例和AO正负异常典型个例分析表明：SEA波列东传过程中,当北非副高偏东偏北，中心在阿拉伯海北部并向巴基斯坦凸出时，阿拉伯海反气旋北部的外围气流与地中海-北非槽前气流叠加，增强了高原西侧向北向南的高原绕流，使“北脊南槽”增强。反气旋东部在印度的北风也增强了南支槽后偏北风，使槽向南加深。当西太副高偏强偏西时，外围气流在孟湾东部至中南半岛与南支槽前西南气流叠加，形成强西南气流伸向云南。偏强稳定的西太副高使南支槽移动缓慢，西南气流和云南降水持续时间较长，强降水区域与强西南气流位置对应。冬季副高偏弱偏南，协同作用弱导致降水弱，所以AO负位相时与降水的关系显著而正位相时不显著。春季副高偏强偏北，协同作用强，西太副高偏西的外围气流对云南降水影响也较大，所以AO正位相与降水相关显著而负位相不显著。AO影响降水有El Niño时显著，La Niña时不显著的特征，与两种状态副高的特征有关。AO指数上升及峰值附近易出现降水，在冬春季干旱严重期间AO都持续较长时间负位相。欧洲脊和地中海-北非槽可作为南支槽影响云南前兆信号，副高位置及强度可作为降水量级预报的依据，研究成果已在业务中应用。