青藏高原低频振荡空间结构的配置特征及其对我国天气气候的影响

In the past, about the Atmospheric Low-Frequency Oscillation over Tibetan Plateau and its influence on eastern China’s weather-climate are more concentrated in the summer, but it is relatively few attention for the low frequency oscillation over Tibetan Plateau in winter. Onetime, some studies also pay attention that the vertical structure of Tibetan plateau low frequency oscillation is between the barotropic and baroclinic structure, sometime is barotropic and another is baroclinic, but there is no reason to analyze its structure change and impact on China's weather and climate events..The project is based on the preliminary results of the preliminary study, to further expand and improve the characteristics of the Tibetan Plateau Atmospheric Low-Frequency Oscillation and its impact on China's weather and climate events. On the one hand, there is a systematic study on the vertical structure and horizontal distribution of the low frequency oscillations over the Tibetan Plateau and the surrounding areas, and the corresponding dynamic thermal mechanism. And then, it is investigated that the impact mechanism of the low frequency circulation system on the East Asian summer monsoon anomaly and the high impact weather events in eastern China due to the low frequency oscillation of the Tibetan Plateau in summer. On the other hand, the variation characteristics of the two zonal wind low frequency oscillation in the North and South Tibetan Plateau are studied; the modulation effect of the corresponding low frequency circulation system on the East Asian Winter Monsoon and its influence on the winter weather events in China. The third is to seek for the early phase signal of the upper reaches Tibetan Plateau Atmospheric changes, which is the significance reference for the extended weather forecast of the eastern China.

过去关于青藏高原大气低频振荡及其对我国天气气候的影响研究多集中于夏季，对冬季高原低频振荡的关注不多；同时也注意到高原低频振荡的垂直结构介于正压和斜压之间，有时是正压结构、有时是斜压结构，但不清楚究其结构变化的原因及对我国天气气候的影响。.本项目是在前期初步研究结果的基础上，拓展和完善青藏高原低频振荡的变化特征及其对我国天气气候的影响研究：第一，系统性研究青藏高原及周边地区大气低频振荡垂直结构和水平配置的变化特征及相应的动力热力机制，探究与夏季高原低频振荡相联系的低频环流系统变化对东亚夏季风异常变化及对我国东部夏季高影响天气事件（大范围持续强降水/高温热浪）的影响机制；第二，研究冬季青藏高原南北两支西风带低频振荡的变化特征，分析相应的低频环流系统变化对东亚冬季风变化的调制作用及其对我国冬季异常低温事件的影响；第三，寻求对我国东部地区延伸期预报有参考意义的上游地区高原大气低频变化的前期信号。

青藏高原热力和动力作用对我国天气气候的影响一直是备受关注的重要问题，项目进一步研究了青藏高原及其周边地区热力作用的低频振荡特征和绕流动力作用对东亚季风及其对我国气温和降水的影响。第一，高原地面热力因子（高原地气温差）低频振荡的水平结构特征及其对高原低涡和高原切变线（简称高原低值系统）发生多（少）的影响。高原低值系统少发年，高原西部和南部地气温差低频振荡是显著的30-60d低频振荡，东部和北部则是10-30d和30-60d两个低频信号；高原低值系统多发年，高原西部的地气温差有两个显著的低频信号，高原中东部仅有30～60d的低频振荡。有65%以上的高原低值系统是在高原地气温差低频信号正位相及其转负位相时段内生成的。第二，表明了高原对流活动异常强（弱）年高原及周边低频振荡的水平和垂直结构特征。青藏高原对流活动异常强（弱）年，对流层大气低频振荡垂直结构在高原西部为斜压（正压）性强、中部为正压（弱斜压）结构、东部都是正压结构，高原北侧是较强（弱）正压结构，高原西南部为正压（斜压）结构、中南部和东南部为斜压结构。第三，超强ENSO背景影响下，我国长江流域和华北-东北区域降水同时出现区域性的异常偏多，受青藏高原和热带海洋低频振荡的影响，两个地区的降水有相反的30-60d的季节内振荡变化特征。第四，揭示了冬季青藏高原南北两支绕流的变化特征及其对冬季气温和降水的影响机制。高原南北两支绕流呈显著的负相关变化，高原北支绕流强、南支绕流弱时，我国东部对流层大气是受纬向风异常影响的“正压结构”，配合相应的经向环流异常，导致35°N两侧区域为反气旋式切变的下沉增温，我国东部气温偏高、降水偏少。高原南支绕流强、北支绕流弱时，纬向风异常则为明显的“斜压结构”，配合相应的经向风异常和华南到华北的异常上升运动，低层“三角形”状的异常冷气团向南切入到我国南海，中上层为异常偏暖的西南气流在冷气团上向北爬升到中高纬度，导致我国大范围的气温异常偏低、降水偏多。