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| Titel |
The equilibrium response to idealized thermal forcings in a comprehensive GCM: implications for recent tropical expansion |
| VerfasserIn |
R. J. Allen, S. C. Sherwood, J. R. Norris, C. S. Zender |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 12, no. 10 ; Nr. 12, no. 10 (2012-05-31), S.4795-4816 |
| Datensatznummer |
250011180
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| Publikation (Nr.) |
 copernicus.org/acp-12-4795-2012.pdf |
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| Zusammenfassung |
| Several recent studies have shown the width of the tropical belt has
increased over the last several decades. The mechanisms driving tropical
expansion are not well known and the recent expansion is underpredicted by
state-of-the art GCMs. We use the CAM3 GCM to investigate how tropical width
responds to idealized atmospheric heat sources, focusing on zonal
displacement of the tropospheric jets. The heat sources include global and
zonally restricted lower-tropospheric warmings and stratospheric coolings,
which coarsely represent possible impacts of ozone or aerosol changes.
Similar to prior studies with simplified GCMs, we find that stratospheric
cooling – particularly at high-latitudes – shifts jets poleward and excites
Northern and Southern Annular Mode (NAM/SAM)-type responses. We also find,
however, that modest heating of the midlatitude boundary layer drives a
similar response; heating at high latitudes provokes a weaker, equatorward
shift and tropical heating produces no shift. Over 70 % of the variance in
annual mean jet displacements across 27 experiments is accounted for by a
newly proposed "Expansion Index", which compares mid-latitude tropospheric
warming to that at other latitudes. We find that previously proposed factors,
including tropopause height and tropospheric stability, do not fully explain
the results. Results suggest recently observed tropical expansion could have
been driven not only by stratospheric cooling, but also by mid-latitude
heating sources due for example to ozone or aerosol changes. |
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