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| Titel |
Cloud-resolving modelling of aerosol indirect effects in idealised radiative-convective equilibrium with interactive and fixed sea surface temperature |
| VerfasserIn |
M. F. Khairoutdinov, C.-E. Yang |
| 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 ; 13, no. 8 ; Nr. 13, no. 8 (2013-04-18), S.4133-4144 |
| Datensatznummer |
250018598
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| Publikation (Nr.) |
 copernicus.org/acp-13-4133-2013.pdf |
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| Zusammenfassung |
| The study attempts to evaluate the aerosol indirect effects over tropical
oceans in regions of deep convection applying a three-dimensional
cloud-resolving model run over a doubly-periodic domain. The Tropics are
modelled using a radiative-convective equilibrium idealisation when the
radiation, turbulence, cloud microphysics and surface fluxes are explicitly
represented while the effects of large-scale circulation are ignored. The
aerosol effects are modelled by varying the number concentration of cloud
condensation nuclei (CCN) at 1% supersaturation, which serves as a proxy
for the aerosol amount in the environment, over a wide range, from pristine
maritime (50 cm−3) to polluted (1000 cm−3) conditions. No direct
effects of aerosol on radiation are included. Two sets of simulations have
been run: fixed (non-interactive) sea surface temperature (SST) and
interactive SST as predicted by a simple slab-ocean model responding to the
surface radiative fluxes and surface enthalpy flux. Both sets of experiments
agree on the tendency of increased aerosol concentrations to make the
shortwave cloud forcing more negative and reduce the longwave cloud forcing
in response to increasing CCN concentration. These, in turn, tend to cool
the SST in interactive-SST case. It is interesting that the absolute change of the
SST and most other bulk quantities depends only on relative change of CCN
concentration; that is, same SST change can be the result of doubling CCN
concentration regardless of clean or polluted conditions. It is found that
the 10-fold increase of CCN concentration can cool the SST by as much as
1.5 K. This is quite comparable to 2.1–2.3 K SST warming obtained in a
simulation for clean maritime conditions, but doubled CO2
concentration. Assuming the aerosol concentration has increased from
preindustrial time by 30%, the radiative forcing due to indirect aerosol
effects is estimated to be −0.3 W m−2. It is found that the indirect
aerosol effect is dominated by the first (Twomey) effect. Qualitative
differences between the interactive and fixed SST cases have been found in
sensitivity of the hydrological cycle to the increase in CCN concentration;
namely, the precipitation rate shows some tendency to increase in fixed SST
case, but robust tendency to decrease in interactive SST case. |
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