Seminário: Tropical Upper Tropospheric Potential Vorticity Intrusions During Sudden Stratospheric Warmings

Data: 
26/10/2015 - 13:00
Local: 
Sala 15 do IAG (Rua do Matão, 1226, Cidade Universitária)

O seminário extra do Departamento de Ciências Atmosféricas será apresentado por John R. Albers, Ph.D (Cooperative Institute for Research in the Environmental Sciences - University of Colorado).
 
 
Tropical Upper Tropospheric Potential Vorticity Intrusions During Sudden Stratospheric Warmings
 
Using reanalysis data we examine extratropical-to-tropical potential vorticity (PV) intrusions in the upper troposphere-lower stratosphere (UTLS) in the weeks surrounding the occurrence of major sudden stratospheric warmings (SSWs). Our analysis reveals that SSW-related PV intrusions are significantly stronger, penetrate more deeply into the tropics, and exhibit unique geographic distributions compared to their climatological counterparts.
While climatological UTLS PV intrusions are generally attributed to synoptic scale Rossby wave breaking, we find that SSW-related PV intrusions are governed by planetary scale wave disturbances that deform the extratropical meridional PV gradient maximum equatorward. As these deformations unfold, planetary-scale wave breaking along the edge of the polar vortex extends deeply into the subtropical and tropical UTLS. In addition, the material PV deformations also reorganize the geographic structure of the UTLS waveguide, which alters where synoptic scale waves break. In combination, these two intrusion mechanisms provide a robust explanation that describes why displacement and split SSWs – or more generally, anomalous stratospheric planetary wavenumber one and two events – exhibit unique geographic centers of action. In particular, displacement SSWs are distinguished by a single PV intrusion maximum over the Pacific Ocean, while split SSWs have PV intrusion maxima over the Pacific and Indian Oceans.
However, the effects of the SSW-related PV intrusions are not confined to the Northern Hemisphere. Our analysis indicates that the impending Northern Hemisphere PV intrusions induce a change to the UTLS tropical and subtropical wind structure that extends deeply into the Southern Hemisphere. The effect of the wind change is manifest as a notable increase in subtropical wave breaking over the Southern Hemisphere Pacific and Indian Ocean basins, which therefore represents a cross-hemispheric remote response to the unfolding SSW. In this work, we explore how the changes in UTLS wind patterns and wave breaking centers of action help modulate tropical and subtropical convection patterns in both ocean basins.