Role of Oceanic SST Fronts in the Interhemispheric Asymmetry of Stratospheric Dynamics and Associated Extremes

The stratospheric dynamics and associated extremes, such as sudden stratospheric warmings (SSWs) and the formation of polar stratospheric clouds (PSCs), exhibit a pronounced interhemispheric asymmetry. SSWs are exceedingly rare in the Antarctic, while the extreme cooling conditions required for the formation of water-based PSCs (Type II) are infrequent and short-lived in the Arctic. To investigate the drivers of this asymmetry, we conducted a series of semi-idealized model experiments, progressing from aqua-planet configurations mimicking Southern Hemisphere (SH) conditions to more realistic Northern Hemisphere (NH) setups.

 

Our results reveal that orography and land-sea thermal contrast (LSCO) alone cannot fully explain the observed interhemispheric asymmetry. Crucially, midlatitude oceanic sea surface temperature (SST) fronts, associated with western boundary currents, play a pivotal role in aligning stratospheric dynamics and extremes with NH-like conditions. Similar to LSCO, SST fronts significantly enhance the stratospheric convergence of planetary wave activity, which strengthens the Brewer-Dobson Circulation. This leads to substantial increases in high-latitude adiabatic warming, elevating the frequency of Arctic SSWs while simultaneously suppressing conditions conducive to PSC formation. These findings highlight the critical yet underexplored role of oceanic SST fronts in shaping the interhemispheric differences in stratospheric dynamics and extremes.