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| Titel |
Calibration of a surface mass balance model for global-scale applications |
| VerfasserIn |
R. H. Giesen, J. Oerlemans  |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1994-0416
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| Digitales Dokument |
URL |
| Erschienen |
In: The Cryosphere ; 6, no. 6 ; Nr. 6, no. 6 (2012-12-07), S.1463-1481 |
| Datensatznummer |
250003878
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| Publikation (Nr.) |
 copernicus.org/tc-6-1463-2012.pdf |
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| Zusammenfassung |
| Global applications of surface mass balance models have large uncertainties,
as a result of poor climate input data and limited availability of mass
balance measurements. This study addresses several possible consequences of
these limitations for the modelled mass balance. This is done by applying a
simple surface mass balance model that only requires air temperature and
precipitation as input data, to glaciers in different regions. In contrast to
other models used in global applications, this model separately calculates
the contributions of net solar radiation and the temperature-dependent fluxes
to the energy balance. We derive a relation for these temperature-dependent
fluxes using automatic weather station (AWS) measurements from glaciers in
different climates. With local, hourly input data, the model is well able to
simulate the observed seasonal variations in the surface energy and mass
balance at the AWS sites. Replacing the hourly local data by monthly gridded
climate data removes summer snowfall and winter melt events and, hence,
influences the modelled mass balance most on locations with a small seasonal
temperature cycle. Modelled winter mass balance profiles are fitted to
observations on 82 glaciers in different regions to determine representative
values for the multiplication factor and vertical gradient of precipitation.
For 75 of the 82 glaciers, the precipitation provided by the climate dataset
has to be multiplied with a factor above unity; the median factor is 2.5. The
vertical precipitation gradient ranges from negative to positive values, with
more positive values for maritime glaciers and a median value of
1.5 mm a−1 m−1. With calibrated precipitation, the modelled
annual mass balance gradient closely resembles the observations on the 82
glaciers, the absolute values are matched by adjusting either the incoming
solar radiation, the temperature-dependent flux or the air temperature. The
mass balance sensitivity to changes in temperature is particularly sensitive
to the chosen calibration method. We additionally calculate the mass balance
sensitivity to changes in incoming solar radiation, revealing that widely
observed variations in irradiance can affect the mass balance by a magnitude
comparable to a 1 °C change in temperature or a 10% change in
precipitation. |
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