This study reveals that the Quasi-Biennial Oscillation (QBO) has a marked impact on the spatial structure of the Arctic Oscillation (AO) in boreal winter. In particular, the North Pacific center (NPC) of the AO is stronger during the westerly phase of the QBO (WQBO) than the easterly phase of the QBO (EQBO). In other words, the variability associated with the AO over the North Pacific is stronger in WQBO years than EQBO years even though the overall variability is insensitive to QBO phase. The QBO is suggested to influence the spatial pattern of the winter AO mainly via modulating the intensity of the stratospheric polar vortex, with a stronger stratospheric polar vortex during WQBO than EQBO years. A stronger stratospheric polar vortex can lead to more planetary wave refraction and facilitate the eastward propagation of wave activity flux from the mid-latitude North Pacific to the North Atlantic. Thus an enhanced connection between North Pacific and North Atlantic atmospheric variability is established, and a more prominent NPC of the AO occurs in WQBO years. In addition, the modulation of the AO structure by the QBO and the associated physical process is supported by output from the CNRM-CM6-1 model. Our results indicate that, for seasonal climate prediction in North America based on the AO, WQBO leads to a wider range of opportunity while EQBO suppresses the opportunity.

Arctic Oscillation,Quasi-Biennial Oscillation,stratospheric polar vortex,planetary waves