Interhemispheric Potential Vorticity Stirring During Sudden Stratospheric Warmings

Using ERA-Interim reanalysis data we examine extratropical-to-tropical potential vorticity (PV) intrusions in the upper troposphere-lower stratosphere in the days and weeks surrounding the occurrence of major sudden stratospheric warmings (SSWs). Our analysis reveals that PV intrusion events that are associated with SSWs are notably different in both geographic location and magnitude when compared to their climatological counterparts.

In particular, while PV intrusions during non-SSW time periods are concentrated in the eastern Pacific and Atlantic Ocean basins where the presence of climatological ‘westerly ducts' supports the propagation of wave energy deep into the tropics, PV intrusion events that are associated with SSWs have unique geographic centers of action that are dependent on the type of SSW involved (i.e. split versus displacement). Our results indicate that the patterns of anomalous PV stirring during SSWs are symmetrical about the equator and are associated with zonally asymmetric shifts in jet structure, anomalously strong barotropic Rossby wave trains, and a secondary, hemispherically symmetric PV response that is centered on the equator. Moreover, we also find that PV intrusions that occur during SSW time periods are significantly stronger and penetrate far more deeply into the tropics than climatological intrusion events.

In light of the strength of the SSW-associated PV intrusion events and their unique geographic centers of action, we consider the implications for how the PV intrusions and associated wave breaking events may modulate tropical convection, the mixing of trace constituents, and the Brewer-Dobson circulation in both hemispheres.