东亚冬季风典型环流型的次季节涡旋反馈机制及其对可预报性的影响

The East Asian Winter Monsoon (EAWM) is a key circulation system affecting the winter climate in East Asia, including the Siberian high, the East Asian trough and the upper westerly jet, et al. EAWM not only features strong interannual variation, but also has significant sub-seasonal variability. At present, the scientific community has limited knowledge about EAWM sub-seasonal variability so that the effective predictable information cannot be provided. It is necessary to have a deeper understanding of the physical mechanisms associated with the EAWM sub-seasonal variability. Noting that the feedback between synoptic eddies (SEs) and low-frequency (LF) flow plays an essential role in the maintenance of extra tropic LF variability, resulting in a longer persistence of LF atmospheric variability. Therefore, this project will reveal the time period and major modes of the typical EAWM circulation patterns in terms of its sub-seasonal variability. On this basis, the characteristics and physical mechanisms of SE feedback are discussed from the viewpoints of dynamic and thermal feedbacks. The effects of SE feedback on the growth, maintenance, propagation and persistence of the typical circulation patterns of EAWM will be explored. Finally, the effect of anomalous SE feedback on the predictability of the typical EAWM circulation patterns is investigated. This project will help to advance our knowledge about the sub-seasonal variability of EAWM and its physical mechanisms, which is crucial to improve the sub-seasonal prediction of EAWM.

东亚冬季风（EAWM）是影响东亚冬季气候的关键系统，包括有西伯利亚高压、东亚大槽以及高空西风急流等典型环流型，不仅有较强的年际变率，而且也具有显著的次季节变率。目前，科学界对EAWM次季节变率的认识十分有限，因此不能提供有效的可预报信息，需要从物理机制上有更加深刻的认识。天气尺度涡旋与低频流之间的反馈对于中高纬大气低频变率的维持起着重要的作用，可以使其产生更长的时间持续性。因此，本项目拟针对EAWM典型环流型的次季节变率，确立其周期和主模态；从动力反馈和热力反馈两方面揭示其涡旋反馈的特征和物理机制，并探究涡旋反馈对其增长、维持、传播和持续性的作用；最后考察涡旋反馈对EAWM典型环流型的次季节可预报性的影响。本项目的开展将加深理解EAWM的次季节变率和机制，为提高EAWM次季节预测水平提供科学依据。

西伯利亚高压、阿留申低压、冬季风等是东亚冬季风系统最典型的环流型，其次季节变化可以影响冷空气的爆发和寒潮的自北向南侵袭，对东亚地区造成严重的低温雨雪等灾害。天气尺度涡旋和低频流之间的正反馈机制在维持中高纬大气低频变率中起着重要的作用，对于气候模态的增长和维持是不可或缺的。本项目揭示了东亚冬季风典型环流型在次季节尺度上的涡旋动力反馈和热力反馈的特征及其物理机制，探究了涡旋反馈对其增长、维持、传播和持续性上的作用。结果表明，涡旋动力反馈对于东亚冬季风典型环流型的维持和增长起到正反馈作用，涡旋热力反馈对于涡旋动力反馈起到调制。并且强的涡旋反馈对于东亚冬季风典型环流型次季节变率的传播和维持都起到促进作用。在此基础上，结合模式预测产品，进一步研究了涡旋反馈对东亚冬季风典型环流型次季节可预报性的影响，结果表明强涡旋动力反馈作用下，东亚冬季风典型环流型具有更高的预报技巧。通过本项研究，有望深刻理解东亚冬季风在次季节尺度上的物理机制以及可预报性特征，为提高东亚冬季风的次季节预报水平提供借鉴与参考。