Dependency of the North Pacific winter storm tracks on the zonal distribution of MJO convection

Abstract

We investigate the effects of the tropical Madden Julian Oscillation (MJO) convection on the zonal location and intensity of storm activity during the boreal cool season (Nov. 1 to Feb. 28, 120 days) over the Pacific Ocean. As tropical convection shifts eastward from the eastern Indian Ocean to the western North Pacific, MJO‐induced local Hadley circulation leads to an eastward displacement of extratropical Rossby Wave Source (RWS). Consequently, this influence leads to an eastward shift of the peak area of the storm track. The storm track is strongest with the MJO convection over the eastern Indian Ocean (phase 3), and it experiences the suppression when MJO convection is located over the Maritime continents (phase 4), and it increases again when the MJO propagates to the western Pacific (phase 5), after which it weakens again (phase 6). The intensity of the storm track, particularly over the western North Pacific (120°E–180°), is determined by the integrated effects of three factors: the midlatitude convective forcing (MCF), the jet stream, and RWS. These factors are associated with the locations of MJO convections. It is estimated that MJO‐induced suppression accounts for only 2.5% of the total observed midwinter suppression (MWS). However, the pattern generated by the MJO is remarkably similar to the observed meridional displacement of North Pacific storm track associated with sub‐seasonal variation. We conclude that the spatial distribution of MJO affects the variation of the Pacific storm track, but is not a cause of the MWS.