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Sensitivity of the Stratospheric Circulation to the Latitude of Thermal Surface Forcing**.

Authors :
Winter, Barbara
Bourqui, Michel S.
Source :
Journal of Climate; Oct2011, Vol. 24 Issue 20, p5397-5415, 19p, 1 Chart, 8 Maps
Publication Year :
2011

Abstract

Using the chemistry climate model Intermediate General Circulation Model-Fast Stratospheric Ozone Chemistry (IGCM-FASTOC), the authors analyze the response in the Northern Hemisphere winter stratosphere to idealized thermal forcing imposed at the surface. The forcing is a 2-K temperature anomaly added to the control surface temperature at all grid points within a latitudinal window of 10° or 30°. The bandwise forcing is applied systematically throughout all latitudes of the Northern Hemisphere. Thermal forcing applied anywhere equatorward of 20°N, or continuously from the equator to 30°N, increases planetary-wave generation in the troposphere and enhances the flux of wave activity propagating vertically into the stratosphere. Consequently, a greater flux of wave activity breaks in the polar vortex, increasing the Brewer-Dobson circulation and leading to a warm anomaly in the polar stratosphere. Ozone concentration increases at high latitudes and decreases at low latitudes. Thermal surface forcing imposed between 30° and 60°N has the reverse effect-decreased planetary-wave generation in the lower troposphere and reduced vertically propagating wave flux entering the stratosphere-and leads to a stronger and colder vortex. Thermal forcing applied poleward of 60°N has little effect on the tropospheric mean state but nonetheless decreases the planetary-scale eddy heat flux from the surface to the tropopause, resulting in a sufficient decrease of the vertical flux of wave activity for the vortex to be anomalously strong and cold. When surface forcing is imposed only poleward of 30°N, ozone concentration decreases at high latitudes but is not affected at low latitudes. Combining the forcing in an equatorial and an extratropical band leads to a response similar to that of the equatorial forcing, demonstrating that the subtropical surface temperature changes determine the sign of the surface-driven response in the vortex. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
08948755
Volume :
24
Issue :
20
Database :
Complementary Index
Journal :
Journal of Climate
Publication Type :
Academic Journal
Accession number :
66853460
Full Text :
https://doi.org/10.1175/2011JCLI4006.1