Modulation of the Aleutian–Icelandic low seesaw and its surface impacts by the Atlantic Multidecadal Oscillation

Abstract

Early studies suggested that the Aleutian–Icelandic low seesaw (AIS) features multidecadal variation. In this study, the multidecadal modulation of the AIS and associated surface climate by the Atlantic Multidecadal Oscillation (AMO) during late winter (February–March) is explored with observational data. It is shown that, in the cold phase of the AMO (AMO|−), a clear AIS is established, while this is not the case in the warm phase of the AMO (AMO|+). The surface climate over Eurasia is significantly influenced by the AMO’s modulation of the Aleutian low (AL). For example, the weak AL in AMO|− displays warmer surface temperatures over the entire Far East and along the Russian Arctic coast and into Northern Europe, but only over the Russian Far East in AMO|+. Similarly, precipitation decreases over central Europe with the weak AL in AMO|−, but decreases over northern Europe and increases over southern Europe in AMO|+.

The mechanism underlying the influence of AMO|− on the AIS can be described as follows: AMO|− weakens the upward component of the Eliassen–Palm flux along the polar waveguide by reducing atmospheric blocking occurrence over the Euro–Atlantic sector, and hence drives an enhanced stratospheric polar vortex. With the intensified polar night jet, the wave trains originating over the central North Pacific can propagate horizontally through North America and extend into the North Atlantic, favoring an eastward-extended Pacific–North America–Atlantic pattern, and resulting in a significant AIS at the surface during late winter.

摘要

早期研究表明了阿留申-冰岛低压振荡的多年代际变化, 本文主要利用观测资料揭示了北大西洋多年代际振荡(AMO)对后冬(2-3月)阿留申-冰岛低压振荡、以及相关地表气候的多年代际调制作用. 结果表明, 只有在AMO冷位相的背景下, 显著的阿留申-冰岛低压振荡才会形成. AMO对阿留申低压的调制作用对欧亚地表气候有显著影响, 比如, 在AMO冷位相背景下, 弱的阿留申低压对应整个东亚地区、以及从俄罗斯北极沿岸到欧洲北部的气温偏高;而在AMO暖位相时, 暖异常只出现在俄罗斯远东地区. 类似地, AMO冷位相对弱阿留申低压的调制, 使得欧洲中部降水减少;而在AMO暖位相的调制下, 欧洲北部降水减少、南部降水增多.

AMO冷位相影响阿留申-冰岛低压振荡的机制解释如下:AMO冷位相通过减少欧洲-北大西洋大气阻塞的发生频次, 使得通过极地波导向上传播的行星波减弱, 平流层极涡加强. 因此, 由于极夜急流的加强, 从北太平洋中部激发的波列可以从北美传播到北大西洋, 有助于向东延伸的太平洋-北美-大西洋型的形成. 最终, 在后冬出现显著的阿留申-冰岛低压振荡.