北太平洋冬季风暴轴异常对西风急流南北位置变动的维持机理

During recent decades, both the westerly jet stream and storm tracks move pole-ward on the South and North Hemispheres, indicating a significant adjustment of the circulation at mid-latitudes. However, the jet stream and storm track over the North Pacific show no trend of northward-movement. The spatial displacement of storm track is in conjunction with the jet stream shift in the same direction on interannual time-scale. This project is based on the conjunction relationship between winter storm track and jet stream over the North Pacific. It focuses on the key issue of mechanism interpretation of the winter storm track anomaly on poleward / equatorward shift of westerly jet stream over the North Pacific. The wintertime cyclonic and anti-cyclonic wave breaking events under the condition of location anomaly of jet stream will be investigated. The related anomalies of synoptic-scale eddy momentum flux convergence and barotropic momentum conversions between the jet and the storm track will also be examined by diagnostic analysis, dynamical studies and model simulation. Therefore, the essential dynamical feedback of storm track on the reinforcement of jet stream anomaly can be understood. Moreover, the project will also consider the process that the lower-level storm track anomaly may influence the atmosphere temperature via air-sea heat flux exchange. Through above studies, we hope to elucidate the mechanism of the winter storm track anomalies at lower- and high-level on poleward / equatorward shift of westerly jet stream over the North Pacific, and understand the unique mechanism of persistent anomaly of jet stream over the North Pacific.

近几十年来南北半球西风急流带和风暴轴总体存在向极移动现象，预示着中纬度地区大气环流的重大调整。然而，北太平洋地区急流和风暴轴均没有北移趋势，而是年际尺度上急流和风暴轴位置的一致性异常偏南或偏北。本项目立足于北太平洋冬季风暴轴与高空西风急流年际异常的这种共生关系，以风暴轴异常对急流位置变动的维持机理研究为核心，利用诊断分析、动力学分析和数值模拟方法，分析冬季急流位置异常年份里气旋式和反气旋式波破碎事件的总体情况，探讨相关联的天气尺度瞬变动量通量的异常辐合辐散以及风暴轴与急流间的正压能量转换，明确风暴轴异常维持急流异常的动力正反馈本质，弄清低层双风暴轴异常通过影响海气感热通量交换继而影响低层大气温度异常场的事实。通过这些研究，揭示冬季高层和低层风暴轴异常对西风急流带位置南北异常变动的维持作用，理解北太平洋急流位置异常维持机制的独特性。

本项目围绕北太平洋冬季天气尺度波破碎事件与急流南北位置异常的联系、北太平洋冬季高层风暴轴异常对急流南北位置异常的动力作用、低层风暴轴异常对急流位置异常的作用，以及全球重要气候信号与风暴轴和急流异常等内容展开研究。揭示了急流位置异常年份里气旋式和反气旋式波破碎的对比情况，探讨相对应的瞬变动量通量的异常辐合辐散对急流异常的动力正反馈本质，初步弄清了低层风暴轴异常通过影响海气感热通量交换继而影响低层大气温度异常场和高层风场的联系，通过这些研究，揭示了冬季高层和低层风暴轴异常对西风急流南北位置异常变动的维持作用，揭示了全球气候事件（PDO/NPGO/ENSO/印太海盆增暖)与风暴轴-急流的联系,特别分析了经典厄尔尼诺和中太平洋型厄尔尼诺时平均流-风暴轴相互作用与Rossby波破碎问题，PDO和NPGO与大尺度环流、风暴轴及水汽输送异常，印太海盆增暖对北太平洋风暴轴和急流异常的影响。所得结果对深入认识东亚-北太平洋冬季大气环流异常的维持机制及其独特性、提高我国气候预测水平有重要的理论意义和应用价值。

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