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| Titel |
Clear-sky radiation trends derived from ground-based observations of surface solar radiation over Europe |
| VerfasserIn |
Blanka Bartok, Maria Z. Hakuba, Arturo Sanchez-Lorenzo, Martin Wild |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250104696
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| Publikation (Nr.) |
 EGU/EGU2015-4127.pdf |
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| Zusammenfassung |
| Trends in clear-sky radiation reflect the changes in the radiatively active components of the
atmosphere without considering the effect of clouds. In this way analyzing the long term
changes in clear-sky radiation gives a better overview over the changes in aerosol content in
the atmosphere, having significant direct radiative effect on surface solar radiation
but no long term records of direct aerosol measurements exist. In this study, the
linear trends of clear-sky radiation records over Europe are analyzed based on daily
observations from 26 stations for the period of 1964-2013, which have been obtained from
the Word Radiation Data Center (WRDC). The daily data has been checked for
temporal homogeneity by applying the MASH method (Szentimrey, 2003). The
separation of clear-sky situation is elaborated using three approaches. In the first
approach the clear-sky situations are detected based on a clearness index, namely the
ratio of the surface solar radiation to the extraterrestrial solar irradiation. In the
second approach the observed values of surface solar radiation are compared to the
climatology of clear-sky surface solar radiation calculated by the MAGIC radiation code
(Muller et al. 2009). In the third approach clear-sky days are detected based on
synoptic cloudiness observations. Overall, in all approaches the trends of clear-sky
radiation may also depend on the thresholds of clear-sky days. Consequently, in order
to eliminate this methodological error in all cases different thresholds are chosen
and the sensitivity of clear-sky radiation trends with respect to the thresholds is
quantified. In order to verify the reliability of the empirical thresholds, a verification of
clear-sky detection is envisaged through a comparison with the values obtained by a
high time resolution clear-sky detection and interpolation algorithm (Long and
Ackermann, 2000) making use of the high quality data from the Baseline Surface
Radiation Network (BSRN).The trends of clear sky radiation calculated by the
different approaches will be compared to estimate the uncertainties introduced by
the different methods. Furthermore, trends will be calculated for different periods
as well, in order to highlight the changes in aerosol content over the investigated
period.
References
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measurements and calculation of downwelling shortwave cloud effects, J. Geophys. Res.,
105(D12), 15609–15626, doi:10.1029/2000JD900077.
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operational scheme for the satellite based retrieval of solar surface irradiance - a LUT based
eigenvector hybrid approach, Remote Sensing of Environment, 113 (5), 1012–1024,
doi:10.1016/j.rse.2009. 01.012
Szentimrey T. 2003. Multiple analysis of series for homogenization (MASH); Veri?cation
procedure for homogenized time series, In: Fourth seminar for homogenization and quality
control in climatological databases, Budapest, Hungary, WMO-TD No. 1236, WCDMP No.
56:193–201. |
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