Using ERA-Interim reanalysis data and ensemble forecasts from the Global Ensemble Forecast System (GEFS), we explore the roles of the Arctic stratospheric polar vortex throughout the life cycle of the 2016 East Asian cold air outbreak (CAO). Our results reveal the distinct roles of the stratosphere in the initiation and intensification stages of this CAO. The occurrence of this CAO was directly related to an exceptionally strong Ural blocking ridge that advected cold air mass toward East Asia. Notably, the strengthening of Ural blocking is largely influenced by the behavior of the stratospheric polar vortex. Specifically, the contraction of the polar vortex toward the western Urals paved the way for reflecting planetary waves originating from the North Atlantic via changing the buoyancy frequency just above the tropopause. The reflected waves converged over the western Urals and acted to strengthen Ural blocking that in turn affected this CAO. Subsequently, an elongation of the polar vortex toward East Asia was observed, leading to a significant descent of the tropopause over East Asia. According to the invertibility theory of potential vorticity, the descending tropopause likely induced a cyclonic anomaly over East Asia, further contributing to the intensification of this CAO. However, the impact of this cyclonic anomaly induced by the polar vortex elongation is relatively limited compared to the influence of Ural blocking. In summary, our study highlights that the geometry of the polar vortex, rather than its strength, is crucial in understanding the stratospheric impacts on the 2016 East Asian CAO.

中文翻译：

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平流层极地涡旋在 2016 年东亚冷空气爆发的开始和增强阶段的不同作用


使用 ERA-Interim 再分析数据和来自全球集成预报系统 （GEFS） 的集成预报，我们探讨了北极平流层极地涡旋在 2016 年东亚冷空气爆发 （CAO） 的整个生命周期中的作用。我们的结果揭示了平流层在该 CAO 的起始和增强阶段的不同作用。这次 CAO 的发生与一个异常强的乌拉尔阻塞脊直接相关，该脊将冷气团平流到东亚。值得注意的是，乌拉尔阻塞的加强在很大程度上受到平流层极涡行为的影响。具体来说，极地涡旋向乌拉尔西部的收缩，通过改变对流层顶上方的浮力频率，为反射源自北大西洋的行星波铺平了道路。反射波在乌拉尔西部汇合并加强了乌拉尔阻塞，进而影响了这个 CAO。随后，观察到极涡向东亚伸长，导致对流层顶在东亚上空显着下降。根据潜在涡度的可逆性理论，下降的对流层顶可能在东亚上空引发了气旋异常，进一步促进了这种 CAO 的增强。然而，与 Ural 阻塞的影响相比，极涡伸长引起的这种气旋异常的影响相对有限。总之，我们的研究强调，极地涡旋的几何形状，而不是它的强度，对于理解平流层对 2016 年东亚 CAO 的影响至关重要。