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| Titel |
Solar irradiance at the earth's surface: long-term behavior observed at the South Pole |
| VerfasserIn |
J. E. Frederick, A. L. Hodge |
| 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 ; 11, no. 3 ; Nr. 11, no. 3 (2011-02-11), S.1177-1189 |
| Datensatznummer |
250009300
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| Publikation (Nr.) |
 copernicus.org/acp-11-1177-2011.pdf |
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| Zusammenfassung |
| This research examines a 17-year database of UV-A (320–400 nm) and visible
(400–600 nm) solar irradiance obtained by a scanning spectroradiometer
located at the South Pole. The goal is to define the variability in solar
irradiance reaching the polar surface, with emphasis on the influence of
cloudiness and on identifying systematic trends and possible links to the
solar cycle. To eliminate changes associated with the varying solar
elevation, the analysis focuses on data averaged over 30–35 day periods
centered on each year's austral summer solstice. The long-term average
effect of South Polar clouds is a small attenuation, with the mean measured
irradiances being about 5–6% less than the clear-sky values, although at
any specific time clouds may reduce or enhance the signal that reaches the
sensor. The instantaneous fractional attenuation or enhancement is
wavelength dependent, where the percent deviation from the clear-sky
irradiance at 400–600 nm is typically 2.5 times that at 320–340 nm. When
averaged over the period near each year's summer solstice, significant
correlations appear between irradiances at all wavelengths and the solar
cycle as measured by the 10.7 cm solar radio flux. An approximate 1.8 ± 1.0%
decrease in ground-level irradiance occurs from solar maximum to
solar minimum for the wavelength band 320–400 nm. The corresponding decrease
for 400–600 nm is 2.4 ± 1.9%. The best-estimate declines appear too
large to originate in the sun. If the correlations have a geophysical
origin, they suggest a small variation in atmospheric attenuation with the
solar cycle over the period of observation, with the greatest attenuation
occurring at solar minimum. |
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