东亚冬季风气候变异和机理以及平流层过程的影响

Climate Variability and Mechanisms of the East Asian Winter Monsoon and the Impact from the Stratosphere

本文综述了近几年来关于东亚冬季风变异特征和机理方面的研究,特别对平流层过程对东亚冬季风和气候异常的可能影响作了回顾和进一步分析。东亚冬季风的变异除了季风强弱变化外,还有东亚冬季风的路径变化;研究表明,前者往往对应全国气温一致的变化,而后者可以引起我国气温的南北反相振荡,并导致东亚冬季风变异存在南北两个子系统。此外,进入本世纪后,东亚冬季风的建立推迟,并且东亚冬季风在盛期明显减弱,但冬季风活动在早春比以往要更为活跃,这些变化与冬季气温南北反相变化也有密切的联系。进一步的分析揭示出东亚气温的南北反相变化是东亚冬季风变异的主要模态之一,而且它与平流层极涡强度密切相关。当异常的平流层极涡向下传播时,可以引起对流层低层北极涛动(AO)的异常以及西伯利亚高压的异常,并在东亚地区出现南北反相的温度变化。有关东亚冬季风变异的成因研究表明,上世纪70年代中后期以后,热带厄尔尼诺-南方涛动(ENSO)的影响变弱,而中高纬的北太平洋涛动(NPO)和乌拉尔地区阻塞强度的影响显著增强,相关研究还揭示了这些变化的原因。此外,东亚冬季风在1987年以后的持续减弱主要与准定常行星波活动年代际变化有关,行星波活动通过波流相互作用可以影响AO以及西伯利亚高压和阿留申低压,从而导致冬季风异常。最后,本文还讨论了太阳活动11年周期变化对东亚冬季气候异常的可能影响和过程。

Recent advances in studies on the characteristics and mechanisms of the East Asian winter monsoon （EAWM） variability are reviewed in the paper. In particular, the possible effect of the stratospheric process on the EAWM and the climate anomalies are documented and investigated. It was found that the path of the EAWM, as well as the variation in its intensity, is important. The EAWM intensity is usually associated with uniform changes in wintertime temperature throughout China, whereas the EAWM path tends to induce a north-south temperature dipole pattern which is associated with two sub-systems that develop in the north and the south of China. Moreover, since the beginning of this century the forming of the EAWM was delayed while its intensity tended to decrease during the mature phase of the monsoon and intensify in early spring compared to earlier records. All these variations are shown to be closely related to the north-south temperature dipole pattern. Further analysis indicates that the north-south dipole pattern is one of the major modes of the EAWM variability and is closely associated with the intensity of the stratospheric Polar Vortex. When an anomalous polar vortex propagates downward, this may induce anomalous Arctic Oscillation （AO） and Siberian High in the lower troposphere, leading to the emergence of a north-south temperature dipole pattern in East Asia. Studies on the causes of EAWM variability suggest that the impact of the E1 Nino-Southern Oscillation （ENSO） has weakened since the mid-late 1970s. In contrast, the impacts from the circulation anomalies in the mid-high latitudes such as the North Pacific Oscillation （NPO） and the Ural blocking have increased significantly. The mechanisms involved have also been investigated. In addition, the persistent weakening of the EAWM since 1987 may be related to the interdecadal change of the quasi-stationary planetary wave activity. Through wave-flow interaction the planetary wave activity may induce variations in the AO, the Siberian High, and the Aleutian Low, and result in anomalous EAWM. Finally, the possible effects of the 11-year solar cycle on the East Asian climate anomalies during the boreal winter and the associated processes are also discussed.