Modulation of the MJO and North Pacific storm track relationship by the QBO

Abstract

This study demonstrates a possible impact of the quasi-biennial oscillation (QBO) on the Madden-Julian Oscillation (MJO)-related North Pacific storm track (NPST) change during October-March for the period of 1979-2016. The NPST shows significant intraseasonal changes in response to the MJO. In general, when the MJO convection is located over the Indian Ocean (western to central Pacific), the NPST tends to shift poleward (southward). This MJO-related NPST change has larger amplitude during the easterly phase of the QBO (EQBO) than during its westerly phase (WQBO). The spatial distribution of this NPST change also exhibits significant differences between the two QBO phases with a zonally elongated pattern during EQBO winters but separated into two centers during WQBO winters. Diagnoses of the dynamical processes associated with the NPST change indicate the dominant roles of the baroclinic energy conversion and downstream energy propagation. The analysis of intraseasonal flow change indicates a larger amplitude of the MJO-related baroclinicity over the North Pacific. This is likely due to a stronger MJO and associated Rossby wave source in EQBO winters, which may give rise to the enhanced amplitude of the NPST change. On the other hand, different spatial distribution of the NPST change is likely a result of a direct impact of the QBO on the NPST. These results suggest that the QBO impact needs to be considered for better reproduction of the MJO-NPST teleconnection in general circulation models, which may also benefit subseasonal prediction of extratropical storm activities.