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| Titel |
Sensitivity of aerosol optical thickness and aerosol direct radiative effect to relative humidity |
| VerfasserIn |
H. Bian, M. Chin, J. M. Rodriguez, H. Yu, J. E. Penner, S. Strahan |
| 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 ; 9, no. 7 ; Nr. 9, no. 7 (2009-04-02), S.2375-2386 |
| Datensatznummer |
250007156
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| Publikation (Nr.) |
 copernicus.org/acp-9-2375-2009.pdf |
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| Zusammenfassung |
| We present a sensitivity study of the effects of spatial and temporal
resolution of atmospheric relative humidity (RH) on calculated aerosol
optical thickness (AOT) and the aerosol direct radiative effects (DRE) in a
global model. We carry out different modeling experiments using the same
aerosol fields simulated in the Global Modeling Initiative (GMI) model at a
resolution of 2° latitude by 2.5° longitude, using time-averaged
fields archived every three hours by the Goddard Earth Observation System
Version 4 (GEOS-4), but we change the horizontal and temporal resolution of
the relative humidity fields. We find that, on a global average, the AOT
calculated using RH at a 1°×1.25° horizontal resolution is 11%
higher than that using RH at a 2°×2.5° resolution, and the
corresponding DRE at the top of the atmosphere is 8–9% and 15% more
negative (i.e., more cooling) for total aerosols and anthropogenic aerosol
alone, respectively, in the finer spatial resolution case. The difference is
largest over surface escarpment regions (e.g. >200% over the Andes
Mountains) where RH varies substantially with surface terrain. The largest
zonal mean AOT difference occurs at 50–60° N (16–21%), where AOT is
also relatively larger. A similar impact is also found when the time
resolution of RH is increased. This increase of AOT and aerosol cooling with
the increase of model resolution is due to the highly non-linear
relationship between RH and the aerosol mass extinction efficiency (MEE) at
high RH (>80%). Our study is a specific example of the uncertainty in
model results highlighted by multi-model comparisons such as AeroCom, and
points out one of the many inter-model differences that can contribute to
the overall spread among models. |
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