Northern Hemisphere mid-winter vortex-displacement and vortex-split stratospheric sudden warmings: Influence of the Madden-Julian Oscillation and Quasi-Biennial Oscillation

摘要

We investigate the connection between the equatorial Madden-Julian Oscillation (MJO) and different types of the Northern Hemisphere mid-winter major stratospheric sudden warmings (SSWs), i.e., vortex-displacement and vortex-split SSWs. The MJO-SSW relationship for vortex-split SSWs is stronger than that for vortex-displacement SSWs, as a result of the stronger and more coherent eastward propagating MJOs before vortex-split SSWs than those before vortex-displacement SSWs. Composite analysis indicates that both the intensity and propagation features of MJO may influence the MJO-related circulation pattern at high latitudes and the type of SSWs. A pronounced Quasi-Biennial Oscillation (QBO) dependence is found for vortex-displacement and vortex-split SSWs, with vortex-displacement (-split) SSWs occurring preferentially in easterly (westerly) QBO phases. The lagged composites suggest that theMJO-related anomalies in the Arctic are very likely initiated when the MJO-related convection is active over the equatorial Indian Ocean (around the MJO phase 3). Further analysis suggests that the QBO may modulate the MJO-related wave disturbances via its influence on the upper tropospheric subtropical jet. As a result, the MJO-related circulation pattern in the Arctic tends to be wave number-one/wave number-two ~25–30 days following phase 3 (i.e., approximately phases 7–8, when the MJO-related convection is active over the western Pacific) during easterly/westerly QBO phases, which resembles the circulation pattern associated with vortex-displacement/vortex-split SSWs.