The Composite Life Cycle of West Pacific Jet Superposition Events and their Associated Large-Scale Environments

A recent study by Handlos and Martin (2016) investigated the large-scale environments conducive to producing a vertical alignment of the polar and subtropical jet streams in the West Pacific.  They showed that these events most often occur during boreal winter, and that their formation arises from the interaction between East Asian Winter Monsoon (EAWM) cold surge events, lower latitude convection and internal jet dynamics.

While their study provides insight regarding the development of superposition events, the evolution of these features after superposition is not well understood.  The goal of this study is to explore the evolution of the large-scale environments associated with these events post-superposition and the significance of that evolution on aspects of the wintertime Northern Hemisphere general circulation.

We utilize the objective jet identification scheme and composite analysis technique from Handlos and Martin (2016) for boreal winters (DJF) 1979/80-2009/10 to consider the composite temporal evolution of West Pacific superposed jet events.  We find that the post-superposition West Pacific jet extends eastward associated with an anomalous positive/negative PV couplet straddling the jet’s exit region.  This feature is shown to occur consistently amongst all cases considered in the composite without regard for the seasonal strength of the EAWM.  The implications of the resulting extended jet on the Northern Hemisphere large-scale circulation is described.