大气准定常行星波异常传播及其在平流层影响东亚冬季气候中的作用

Anomalous Propagation of the Quasi-stationary Planetary Waves in the Atmosphere and Its Roles in the Impact of the Stratosphere on the East Asian Winter Climate

东亚季风区同时受世界上最广阔的大洋和陆地的影响,这种行星尺度的海陆热力对比以及青藏高原大地形的作用,从而产生很强的行星尺度扰动,并且这种扰动具有准定常的性质。利用再分析资料研究了准定常行星波活动的变化对东亚地区冬季气候异常的影响,主要侧重于年际和季节内时间尺度上的变化。在年际时间尺度上,冬季行星波两支波导的变化存在反相关的振荡关系,这种年际振荡一方面影响了北半球环状模的位相,另外一方面导致了东亚地区的气候异常。当有异常强的低纬波导时,一般对应有西伯利亚高压的减弱和我国东北、华北地区的增温;反之当有异常弱的低纬波导时,我国东北和华北温度则普遍偏低。研究还表明,行星波传播的年际振荡与东亚地区气候异常的关系显著地受到热带平流层准两年周期振荡(QBO)的调制,只是当QBO处于东风位相时,行星波传播的年际振荡才与东亚气候异常有显著的关系。在季节内时间尺度上,准定常行星波的变化与平流层极涡的低频变化密切相关,并且这种平流层极涡的异常通过和行星波的相互作用,可以自上而下影响到对流层的短期气候;平流层极涡异常下传对对流层大气环流有明显的影响,并且这种影响在东亚地区非常显著。由于平流层变化通常维持时间长,并且平流层极涡异常下传领先于对流层,因此这为东亚冬季短期气候异常的预报提供了一个新的预报依据。

East Asian monsoon region is influenced by both the vast ocean and continent in the world. Strong disturbances with planetary scale are forced by this thermal contrast between ocean and continent and the topography of Tibetan Plateau. And these planetary scale disturbances are quasi-stationary. By using the reanalysis dataset the influences of anomalous planetary wave activities on the East Asian winter climate are studied mainly on the interannual and intraseasonal timescales. On the interannual timescale, two waveguides of planetary waves in the northern winter have anti-phase oscillation. On the one hand, this interannual oscillation has an interaction with the Northern Annular Mode. On the other hand, it exerts influence on the climate anomalies over East Asia. During the strong low-latitude waveguide winters, the Siberian high tends to wea and the temperature tends to increase over Northeast China and North China. The situation tends to be reverse during the weak low-latitude waveguide winters. The results also indicate that the relationship between the planetary wave activity and the East Asian winter climate on interannual timescale is strongly modulated by the tropical quasi-biennial oscillation （QBO） of zonal wind in the stratosphere. Only in the QBO easterly phase, the interannual oscillation of planetary wave propagation is closely related to the climate anomalies over East Asia. On the intraseasonal timescale, the variability in the quasi-stationary planetary wave activity is closely associated with the low frequency variation of stratospheric polar vortex. The results indicate that the anomalous polar vortex in the stratosphere may have a downward influence on the short-term climate in the troposphere via the interaction with the planetary waves. This downward propagation of stratospheric anomalies associated with polar vortex has an evident influence on the general circulation in the troposphere, and the influence is particularly significant over East Asia. Since the stratospheric variability generally has longer times-cales and this downward propagation leads the variations in the troposphere, our research provides a new predictor for the East Asian winter short-term climate anomalies.