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| Titel |
Clouds and the atmospheric circulation response to warming |
| VerfasserIn |
Paulo Ceppi, Dennis Hartmann |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250127763
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| Publikation (Nr.) |
 EGU/EGU2016-7671.pdf |
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| Zusammenfassung |
| We study the effect of clouds on the atmospheric circulation response to CO2 quadrupling in
an aquaplanet model with a slab-ocean lower boundary. The cloud effect is isolated by
locking the clouds to either the control or 4xCO2 state in the shortwave (SW) or longwave
(LW) radiation schemes. In our model, cloud-radiative changes explain more than half of the
total poleward expansion of the Hadley cells, midlatitude jets, and storm tracks under CO2
quadrupling, even though they cause only one-fourth of the total global-mean surface
warming. The effect of clouds on circulation results mainly from the SW cloud-radiative
changes, which strongly enhance the Equator-to-pole temperature gradient at all levels in the
troposphere, favoring stronger and poleward-shifted midlatitude eddies. By contrast,
quadrupling CO2 while holding the clouds fixed causes strong polar amplification and
weakened midlatitude baroclinicity at lower levels, yielding only a small poleward expansion
of the circulation. Our results show that (a) the atmospheric circulation responds
sensitively to cloud-driven changes in meridional and vertical temperature distribution,
and (b) the spatial structure of cloud feedbacks likely plays a dominant role in the
circulation response to greenhouse gas forcing. While the magnitude and spatial structure
of the cloud feedback are expected to be highly model-dependent, an analysis of
4xCO2 simulations of CMIP5 models shows that the SW cloud feedback likely
forces a poleward expansion of the tropospheric circulation in most climate models. |
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