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| Titel |
Effect of surface albedo, water vapour, and atmospheric aerosols on the cloud-free shortwave radiative budget in the Arctic |
| VerfasserIn |
C. Di Biagio, A. G. di Sarra, P. Eriksen, S. E. Ascanius, G. Muscari, B. Holben |
| 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 |
250058704
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| Zusammenfassung |
| The Arctic region plays a central role in the global climate system. As a consequence of
climate changes and global warming in the Arctic we expect a decrease in the surface albedo,
caused by the reduction in both the area covered by snow/ice and the thickness of the
ice-pack, as well as an increase in atmospheric water vapour and atmospheric aerosols, due to
an increase of both the long-range transport and the local production. The surface energy
balance sensitivity to variations in surface albedo (A), water vapour (wv), and aerosol
occurrence is one of the main key factors to evaluate when assessing how the Arctic will
respond to future climate changes.
The main objective of this study is to derive the individual contributions of wv, A, and
atmospheric aerosols in affecting the cloud-free shortwave irradiance (SW) at the surface.
Four years of data of SW, aerosol optical properties, and column wv measured at Thule Air
Base, TAB, (76.5Ë N, 68.8Ë W, Greenland), and co-located satellite observations of A are
used in this study. The measurements are combined with radiative transfer model calculations
in order to reproduce the observed shortwave surface fluxes and to separate the radiative
effect of each parameter.
In the daylight period of the year (March to October at Thule), water vapour varies
between 0.1 and 1.6 cm, with maxima in summer. The surface albedo ranges between 0.66
and 0.05; the melting season occurs typically between mid-May and mid-June. The aerosol
optical depth at 500 nm (Ï) is generally lower than 0.2 and shows an evident seasonal cycle
with larger values in spring, during the haze season, and lower values in summer and early
autumn.
The results of our study indicate that the shortwave radiation at the surface is mainly
affected by water vapour absorption, which produces a reduction of SW as low as -100
Wm-2. The seasonal change of A produces an increase of SW by up to +25 Wm-2. The
annual mean radiative effect is estimated to be –(21-22) Wm-2 for wv, and +(2-3) Wm-2 for
A.
Atmospheric aerosols produce a reduction of SW as low as -32 Wm-2. The instantaneous
aerosol radiative forcing (RFÏ) reaches values of -28 Wm-2 and shows a strong dependency
on surface albedo. The derived radiative forcing efficiency (FEÏ) for solar zenith angles
between 55Ë and 70Ë is estimated to be (-120.6±4.3) Wm-2for 0.1 |
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