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| Titel |
The hemispheric distribution of reflected shortwave radiation in observations and aquaplanet climates |
| VerfasserIn |
A. Voigt, B. Stevens, J. Bader, T. Mauritsen |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250066331
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| Zusammenfassung |
| We present results from an investigation of the hemispheric distribution of reflected
shortwave radiation in observations and in climate model simulations of aquaplanets.
For the present-day Earth, the concentration of land masses and aerosols in the Northern
hemisphere suggests that the Northern hemisphere should reflect more shortwave radiation
than the Southern hemisphere. However, as we show, data from the CERES mission
continues to suggest that the clouds compensate for differences in reflected clear-sky
radiation, so that the difference in the total reflected shortwave radiation, at 0.1 Wm-2, is
indistinguishable from zero. We then devise a variety of methods to estimate the degrees of
freedom in the reflected shortwave radiation. Based on this, we demonstrate that the
hemispheric symmetry in reflected shortwave radiation is likely the consequence of
dynamical processes.
We further perform aquaplanet simulations using ECHAM6 with a perturbed ocean
albedo to study how aquaplanet climates respond to surface albedo perturbations. To focus on
the role of clouds, sea-ice formation is inhibited and ocean heat transport is fixed in the
simulations. The ocean albedo perturbations are asymmetric with respect to the equator such
that their global-mean radiative forcing is zero. The hemisphere with decreased ocean
albedo warms while the hemisphere with increased ocean albedo cools. This leads to
cross-equatorial energy transport from the decreased ocean albedo hemisphere into the
increased ocean albedo hemisphere, which is associated with a shift of the intertropical
convergence zone and deep convective clouds into the darker hemisphere. These tropical
cloud changes work against the imposed ocean albedo perturbation and are an important
mechanism that may contribute to the observed symmetry in hemispheric albedo. |
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