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| Titel |
Simulation of permafrost and seasonal thaw depth in the JULES land surface scheme |
| VerfasserIn |
R. Dankers, E. J. Burke, J. Price |
| 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 ; 5, no. 3 ; Nr. 5, no. 3 (2011-09-27), S.773-790 |
| Datensatznummer |
250002604
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| Publikation (Nr.) |
 copernicus.org/tc-5-773-2011.pdf |
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| Zusammenfassung |
| Land surface models (LSMs) need to be able to simulate realistically the
dynamics of permafrost and frozen ground. In this paper we evaluate the
performance of the LSM JULES (Joint UK Land Environment Simulator), the
stand-alone version of the land surface scheme used in Hadley Centre climate
models, in simulating the large-scale distribution of surface permafrost. In
particular we look at how well the model is able to simulate the seasonal
thaw depth or active layer thickness (ALT). We performed a number of
experiments driven by observation-based climate datasets. Visually there is
a very good agreement between areas with permafrost in JULES and known
permafrost distribution in the Northern Hemisphere, and the model captures
97% of the area where the spatial coverage of the permafrost is at least
50%. However, the model overestimates the total extent as it also
simulates permafrost where it occurs sporadically or only in isolated
patches. Consistent with this we find a cold bias in the simulated soil
temperatures, especially in winter. However, when compared with observations
on end-of-season thaw depth from around the Arctic, the ALT in JULES is
generally too deep. Additional runs at three sites in Alaska demonstrate how
uncertainties in the precipitation input affect the simulation of soil
temperatures by affecting the thickness of the snowpack and therefore the
thermal insulation in winter. In addition, changes in soil moisture content
influence the thermodynamics of soil layers close to freezing. We also
present results from three experiments in which the standard model setup was
modified to improve physical realism of the simulations in permafrost
regions. Extending the soil column to a depth of 60 m and adjusting the soil
parameters for organic content had relatively little effect on the
simulation of permafrost and ALT. A higher vertical resolution improves the
simulation of ALT, although a considerable bias still remains. Future model
development in JULES should focus on a dynamic coupling of soil organic
carbon content and soil thermal and hydraulic properties, as well as
allowing for sub-grid variability in soil types. |
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