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| Titel |
Assessment of BSRN radiation records for the computation of monthly means |
| VerfasserIn |
A. Roesch, M. Wild, A. Ohmura, E. G. Dutton, C. N. Long, T. Zhang |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 4, no. 2 ; Nr. 4, no. 2 (2011-02-23), S.339-354 |
| Datensatznummer |
250001678
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| Publikation (Nr.) |
 copernicus.org/amt-4-339-2011.pdf |
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| Zusammenfassung |
The integrity of the Baseline Surface Radiation Network (BSRN)
radiation monthly averages are assessed
by investigating the impact on monthly means due to the frequency of
data gaps caused by missing or discarded high time
resolution data. The monthly statistics, especially means, are considered
to be important and useful values for climate research, model performance
evaluations and for assessing the quality of satellite (time- and space-averaged)
data products.
The study investigates the spread in different algorithms
that have been applied for the computation of monthly means from 1-min values.
The paper reveals that the computation of
monthly means from 1-min observations distinctly depends on the
method utilized to account for the missing data. The intra-method difference generally
increases with an increasing fraction of missing data.
We found that a substantial fraction of the radiation fluxes observed
at BSRN sites is either missing or flagged as questionable.
The percentage of missing data is 4.4%, 13.0%, and 6.5% for global
radiation, direct shortwave radiation, and downwelling longwave radiation, respectively.
Most flagged data in the shortwave are due to nighttime instrumental noise and
can reasonably be set to zero after correcting for thermal offsets in the daytime data.
The study demonstrates that the handling of flagged data clearly impacts
on monthly mean estimates obtained with different methods.
We showed that the spread of monthly shortwave fluxes is generally clearly
higher than for downwelling longwave radiation.
Overall, BSRN observations provide sufficient
accuracy and completeness for reliable estimates of monthly mean values.
However, the value of future data could be further increased by reducing
the frequency of data gaps and the number of outliers.
It is shown that two independent methods for accounting for the diurnal and seasonal variations in the
missing data permit consistent monthly means to within less than 1 W m−2 in most cases.
The authors suggest using a standardized method for the computation
of monthly means which addresses diurnal variations in the missing data in order to avoid a mismatch
of future published monthly mean radiation fluxes from BSRN.
The application of robust statistics would probably lead to less biased results for data records with
frequent gaps and/or flagged data and outliers. The currently applied empirical methods should, therefore,
be completed by the development of robust methods. |
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