北半球高空急流型态变化影响冬季极端低温过程区域差异的机理研究

The frequent occurrences of winter extreme low temperature process in recent years aroused the attentions of the whole society. This kind of extreme low temperature process with large affected area, long duration and serious disaster shows significant regional differences, which comprehensively reflected the atmospheric circulation anomalies response to external forcing and interaction of weather systems. The evolution of the upper-tropospheric jet stream pattern plays the key role in this process. Therefore, it is necessary to explore the causes and physical mechanism of regional differences in extreme low temperature processes in Northern Hemisphere from the perspective of jet stream variation. Based on site observations and reanalysis data, combing dynamic statistic diagnosis and numerical simulation, the variation of the jet stream in the southward shift process of the polar vortex are deeply studied aiming to winter extreme low temperature process in different regions. The impact of the jet on the amplitude, path and speed of the different planetary waves, as well as the influence on vorticity, momentum and energy transportation of the synoptic scale transient eddies are respectively discussed to further explore its affecting on the position and the maintenance time of large scale trough and ridge anomalies, which primarily determines the occurring region of the extreme low temperature process. On this basis, the response of the jet variation to different Arctic warming mode under the various circulations background will be further studied to seek prediction signal for occurring region of the extreme low temperature process. The work will be helpful for understanding the physical mechanism for winter extreme low temperature processes and improving its predictive ability.

近年来冬季频发的极端低温过程引起了全社会的关注，这类范围大、时间长、灾害重的极端低温过程具有显著的区域差异，是大气环流异常对外强迫响应及大气内部各天气系统相互作用的综合体现，高空急流型态变化是此过程中的关键动力环节。因此，本申请拟基于站点观测和再分析资料，采用动力统计诊断和数值模拟相结合的途径，针对不同区域极端低温过程，分析极涡南下过程中高空急流型态变化特征，探讨急流一方面通过影响北半球大气环流不同波数行星波振幅、路径及波速，另一方面通过影响天气尺度扰动涡度、动量及能量输送，进而影响北半球大尺度长波槽脊（阻塞高压）异常位置及维持时间，最终导致极端低温过程区域差异的物理过程；在此基础上，进一步研究不同环流背景下北极不同增暖模态对高空急流型态变化的可能影响，寻找不同区域极端低温过程发生的前期信号，为深入理解冬季极端低温过程发生机理及提高其预测能力提供理论参考。

全球变暖背景下的群发性极端温度事件引起了全社会的关注，这类事件是大气环流对外强迫的异常响应及大气内部各天气系统相互作用的综合体现，高空急流变化是其关键动力环节。项目利用中国区域观测资料、全球再分析资料及CMIP5/CMIP6不同情景下模拟结果，采用群发性极端温度事件识别方法，建立了极端温度事件过程数据集，并基于重现期视角分析了中国极端温度的区域非一致性，指出了极端温度响应敏感区及可能原因，依据多模式结果预估了其在未来不同增暖情景下的变化。在此基础上，比较了中国不同区域群发性极端低温过程环流特征，揭示了事件发生前期海平面气压系统、高空槽脊及急流的发展和变化差异。研究了冬季东亚高空急流的经向协同变化及热力结构及其与陆面气温型态及海温配置的关系，分析了急流变化对罗斯贝波振幅、移速和路径的影响。指出东亚极锋急流和副热带急流具有经向上的反向移动特征，这种移动与欧亚大陆地面气温的偶极子模态及太平洋海温的类拉尼娜模态密切相关。并以2020/2021年冬季典型个例探讨了冬季冷暖气候转换期间北半球大尺度长波槽脊位置及维持的物理过程，研究表明平流层异常信号逐渐下传至对流层，导致对流层乌山阻高减弱崩溃，东亚副热带急流增强，进而导致冷暖时段的转变，急流变化是这两个事件联系的桥梁。这些研究成果为深入理解急流影响极端温度事件过程机理及提高其预测能力提供了重要的理论参考。