Cyclone-Like Features Within the Stratospheric Polar-Night Vortex

Distinctive synoptic-scale (∼1,500 km) flow features are identified within the core of the stratospheric polar-night vortex at stratopause altitudes (∼50 km). Typically they comprise a train or a complex pattern of transient vortices, each characterized by enhanced values of potential vorticity (PV) and relative vorticity but with a weaker thermal signal. In the MERRA-2 (and two other) reanalysis fields these cyclone-like features persist for several days, occur episodically, and form essentially within the core of the polar-night vortex itself. Their origin is plausibly linked to a form of barotropic instability associated with a radiatively-induced annular ring of enhanced PV. Moreover, their ubiquity and dynamics carries possible implications for: - the structure of the larger-scale polar vortex and its preconditioning ahead of a Sudden Stratospheric Warming event; the distribution of trace-constituents within the core; and the features representation in extended range/seasonal prediction and climate models.