Accessibility navigation


A mechanism for the effect of tropospheric jet structure on the annular mode-like response to stratospheric forcing

Simpson, I. R., Blackburn, M. and Haigh, J. D. (2012) A mechanism for the effect of tropospheric jet structure on the annular mode-like response to stratospheric forcing. Journal of the Atmospheric Sciences, 69 (7). pp. 2152-2170. ISSN 1520-0469

Full text not archived in this repository.

To link to this article DOI: 10.1175/JAS-D-11-0188.1

Abstract/Summary

For many climate forcings the dominant response of the extratropical circulation is a latitudinal shift of the tropospheric mid-latitude jets. The magnitude of this response appears to depend on climatological jet latitude in general circulation models (GCMs): lower latitude jets exhibit a larger shift. The reason for this latitude dependence is investigated for a particular forcing, heating of the equatorial stratosphere, which shifts the jet poleward. Spin-up ensembles with a simplified GCM are used to examine the evolution of the response for five different jet structures. These differ in the latitude of the eddy-driven jet, but have similar sub-tropical zonal winds. It is found that lower latitude jets exhibit a larger response due to stronger tropospheric eddy-mean flow feedbacks. A dominant feedback responsible for enhancing the poleward shift is an enhanced equatorward refraction of the eddies, resulting in an increased momentum flux, poleward of the low latitude critical line. The sensitivity of feedback strength to jet structure is associated with differences in the coherence of this behaviour across the spectrum of eddy phase speeds. In the configurations used, the higher latitude jets have a wider range of critical latitude locations. This reduces the coherence of the momentum flux anomalies associated with different phase speeds, with low phase speeds opposing the effect of high phase speeds. This suggests that, for a given sub-tropical zonal wind strength, the latitude of the eddy driven jet affects the feedback through its influence on the width of the region of westerly winds and the range of critical latitudes on the equatorward flank of the jet.

Item Type:Article
Refereed:Yes
Divisions:Faculty of Science > School of Mathematical and Physical Sciences > Department of Meteorology
Faculty of Science > School of Mathematical and Physical Sciences > NCAS
ID Code:27581
Uncontrolled Keywords: Annular mode, Eddies, Stratophere-troposphere coupling
Publisher:American Meteorological Society

Centaur Editors: Update this record

Page navigation