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| Titel |
Modelling the direct effect of aerosols in the solar near-infrared on a planetary scale |
| VerfasserIn |
N. Hatzianastassiou, C. Matsoukas, A. Fotiadi, P. W. Jr. Stackhouse, P. Koepke, K. G. Pavlakis, I. Vardavas |
| 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 ; 7, no. 12 ; Nr. 7, no. 12 (2007-06-25), S.3211-3229 |
| Datensatznummer |
250005089
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| Publikation (Nr.) |
 copernicus.org/acp-7-3211-2007.pdf |
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| Zusammenfassung |
| We used a spectral radiative transfer model to compute the direct radiative
effect (DRE) of natural plus anthropogenic aerosols in the solar
near-infrared (IR), between 0.85–10 μm, namely, their effect on the
outgoing near-IR radiation at the top of atmosphere (TOA, ΔFTOA),
on the atmospheric absorption of near-IR radiation (ΔFatmab)
and on the surface downward and absorbed near-IR radiation
(ΔFsurf, and ΔFsurfnet, respectively). The
computations were performed on a global scale (over land and ocean) under
all-sky conditions, using detailed spectral aerosol optical properties taken
from the Global Aerosol Data Set (GADS) supplemented by realistic data for
the rest of surface and atmospheric parameters. The computed aerosol DRE,
averaged over the 12-year period 1984–1995 for January and July, shows that
on a global mean basis aerosols produce a planetary cooling by increasing
the scattered near-IR radiation back to space by 0.48 W m−2, they warm
the atmosphere by 0.37 W m−2 and cool the surface by decreasing
the downward and absorbed near-IR radiation at surface by 1.03 and 0.85 W m−2,
respectively. The magnitude of the near-IR aerosol DRE is smaller
than that of the combined ultraviolet (UV) and visible DRE, but it is still
energetically important, since it contributes to the total shortwave (SW)
DRE by 22–31%. The aerosol-produced near-IR surface cooling combined with
the atmospheric warming, may affect the thermal dynamics of the
Earth-atmosphere system, by increasing the atmospheric stability, decreasing
thus cloud formation, and precipitation, especially over desertification
threatened regions such as the Mediterranean basin. This, together with the
fact that the sign of near-IR aerosol DRE is sometimes opposite to that of
UV-visible DRE, demonstrates the importance of performing detailed spectral
computations to provide estimates of the climatic role of aerosols for the
Earth-atmosphere system. This was demonstrated by sensitivity tests
revealing very large differences (up to 300%) between aerosol DREs
computed using detailed spectral and spectrally-averaged aerosol optical
properties. Our model results indicate thus that the aerosol direct
radiative effect on the near-IR radiation is very sensitive to the treatment
of the spectral dependence of aerosol optical properties and solar
radiation. |
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