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| Titel |
Influence of observed diurnal cycles of aerosol optical depth on aerosol direct radiative effect |
| VerfasserIn |
A. Arola, T. F. Eck, J. Huttunen, K. E. J. Lehtinen, A. V. Lindfors, G. Myhre, A. Smirnov, S. N. Tripathi, H. Yu |
| 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. 15 ; Nr. 13, no. 15 (2013-08-15), S.7895-7901 |
| Datensatznummer |
250085630
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| Publikation (Nr.) |
 copernicus.org/acp-13-7895-2013.pdf |
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| Zusammenfassung |
| The diurnal variability of aerosol optical depth (AOD) can be significant,
depending on location and dominant aerosol type. However, these diurnal
cycles have rarely been taken into account in measurement-based estimates of
aerosol direct radiative forcing (ADRF) or aerosol direct radiative effect
(ADRE). The objective of our study was to estimate the influence of diurnal
aerosol variability at the top of the atmosphere ADRE estimates. By including all the possible AERONET sites, we wanted to assess the influence on global
ADRE estimates. While focusing also in more detail on some selected sites
of strongest impact, our goal was to also see the possible impact
regionally.
We calculated ADRE with different assumptions about the daily AOD
variability: taking the observed daily AOD cycle into account and assuming
diurnally constant AOD. Moreover, we estimated the corresponding differences
in ADREs, if the single AOD value for the daily mean was taken from the the
Moderate Resolution Imaging Spectroradiometer (MODIS) Terra or Aqua overpass
times, instead of accounting for the true observed daily variability. The
mean impact of diurnal AOD variability on 24 h ADRE estimates, averaged over
all AERONET sites, was rather small and it was relatively small even for the
cases when AOD was chosen to correspond to the Terra or Aqua overpass time.
This was true on average over all AERONET sites, while clearly there can be
much stronger impact in individual sites. Examples of some selected sites
demonstrated that the strongest observed AOD variability (the strongest
morning afternoon contrast) does not typically result in a significant impact
on 24 h ADRE. In those cases, the morning and afternoon AOD patterns are
opposite and thus the impact on 24 h ADRE, when integrated over all solar
zenith angles, is reduced. The most significant effect on daily ADRE was
induced by AOD cycles with either maximum or minimum AOD close to local noon.
In these cases, the impact on 24 h ADRE was typically around
0.1–0.2 W m−2 (both positive and negative) in absolute values,
5–10% in relative ones. |
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