Summary: | We investigate the connection between the equatorial Maddenâ€Julian Oscillation (MJO) and different types of the Northern Hemisphere midâ€winter major stratospheric sudden warmings (SSWs), i.e., vortexâ€displacement and vortexâ€split SSWs. The MJOâ€SSW relationship for vortexâ€split SSWs is stronger than that for vortexâ€displacement SSWs, as a result of the stronger and more coherent eastward propagating MJOs before vortexâ€split SSWs than those before vortexâ€displacement SSWs. Composite analysis indicates that both the intensity and propagation features of MJO may influence the MJOâ€related circulation pattern at high latitudes and the type of SSWs. A pronounced Quasiâ€Biennial Oscillation (QBO) dependence is found for vortexâ€displacement and vortexâ€split SSWs, with vortexâ€displacement (â€split) SSWs occurring preferentially in easterly (westerly) QBO phases. The lagged composites suggest that the MJOâ€related anomalies in the Arctic are very likely initiated when the MJOâ€related convection is active over the equatorial Indian Ocean (around the MJO phase 3). Further analysis suggests that the QBO may modulate the MJOâ€related wave disturbances via its influence on the upper tropospheric subtropical jet. As a result, the MJOâ€related circulation pattern in the Arctic tends to be wave numberâ€one/wave numberâ€two ~25–30 days following phase 3 (i.e., approximately phases 7–8, when the MJOâ€related convection is active over the western Pacific) during easterly/westerly QBO phases, which resembles the circulation pattern associated with vortexâ€displacement/vortexâ€split SSWs. © 2014. American Geophysical Union. Received 6 APR 2014. Accepted 10 OCT 2014. Accepted article online 13 OCT 2014. Published online 28 NOV 2014. This research was supported by the National Science Foundation award ATMâ€0840755 to University of California, Los Angeles. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and ...
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