南支槽多尺度变率与多维度成因及其机制研究

The southern branch trough (SBT) is a quasi-stationary disturbance in the south-branch westerly in winter half year. The synoptic and climatic scale variability of SBT can greatly influence the winter precipitation in southern china. However, previous studies pay more attention to the influences of SBT on weather and climate of our country, while the features, causes and mechanism of multi-scale variability of the SBT remain unclear. Previous studies mainly focus on the climatic scale variability of SBT, and the influence caused by tropical systems, while the influence of ex-tropical systems and the contribution of synoptic scale variability to the SBT are less concerned. This also leads to the characteristics of SBT intensity remain to be further revealed, and the features and cause of SBT location are not clear. Hence, this program intends to identify the SBT processes by using the synoptic trough identification method and reveal the multi-scale variability of the SBT. A new index will be defined to describe both the synoptic and climatic scale variability of the SBT. Then, according to the new SBT index, the key factors and its mechanisms which influence the variability of intensity and location of SBT will be revealed by using the methods of statistical analysis, dynamical diagnosis and numerical simulations. Finally, the physical concepts of the comprehensive multidimensional influences of the tropical and middle latitude systems to variations of the SBT will be considered to establishing for guiding the SBT forecast.

南支槽是冬半年南支西风气流上的准定常扰动，对我国南方地区降水具有重要影响。以往研究多关注南支槽对我国天气和气候的影响，而对其本身的变化特征、成因及机制关注不够、至今仍不清楚。特别是已有研究主要侧重南支槽强度的气候变率、且重点关注低纬热带强迫因子的影响，未重视中高纬系统和天气尺度变率的贡献，导致所揭示的南支槽强度变率信号不够全面，所展现的位置变异特征与成因也有局限性。因此，本项目拟引入天气过程中槽的判识方法，定量化辨识南支槽天气尺度信号，研究其变化对南支槽强度、位置等在气候变率上的贡献。从天气与气候角度，定义能包含两方面特征的南支槽新指数，并以此为基础，再采用统计分析、动力诊断和数值模拟相结合的方法，探析中高纬大气内部变率过程和低纬热带关键外源强迫因子对南支槽强度、位置的影响及机制，阐明上述两者协同影响南支槽气候变率的物理图像，加深对南支槽多尺度变率及其多维度成因的理解，为其预测提供新依据。

项目提出了基于日资料辨识南支槽及其移动信号的客观辨识新方法，并在此基础上建立了近四十年南支槽事件过程数据库，构建了表征南支槽强度、位置变化的新指数；深入分析了南支槽多维度、多时间尺度变化特征，揭示了高层急流系统影响低层南支槽变率的物理过程和机制；分析了南支槽活动影响我国冬季降水的主要模态及其物理机制，建立了南支槽变化及其影响我国冬季强降水天气的物理概念模型，指出低层南支槽—高层急流协同变化在冬季南方移动型暴雨事件中的作用。研究成果拓展了南支槽变率及其影响降水极端天气方面的新认知，为南支槽相关的预报和预测提供了科学依据。