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| Titel |
Evaluation of North Eurasian snow-off dates in the ECHAM5.4 atmospheric general circulation model |
| VerfasserIn |
P. Räisänen, A. Luomaranta, H. Järvinen, M. Takala, K. Jylhä, O. N. Bulygina, K. Luojus, A. Riihelä, A. Laaksonen, J. Koskinen, J. Pulliainen |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 7, no. 6 ; Nr. 7, no. 6 (2014-12-18), S.3037-3057 |
| Datensatznummer |
250115799
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| Publikation (Nr.) |
 copernicus.org/gmd-7-3037-2014.pdf |
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| Zusammenfassung |
The timing of springtime end of snowmelt (snow-off date) in
northern Eurasia in version 5.4 of the ECHAM5 atmospheric general circulation
model (GCM) is
evaluated through comparison with a snow-off date data set based on
space-borne microwave radiometer measurements and with Russian snow
course data. ECHAM5 reproduces well the observed gross geographical
pattern of snow-off dates, with earliest snow-off (in March) in the
Baltic region and latest snow-off (in June) in the Taymyr Peninsula
and in northeastern parts of the Russian Far East. The primary
biases are (1) a delayed snow-off in southeastern Siberia
(associated with too low springtime temperature and too high surface
albedo, in part due to insufficient shielding by canopy); and (2) an
early bias in the western and northern parts of northern
Eurasia. Several sensitivity experiments were conducted, where
biases in simulated atmospheric circulation were corrected through
nudging and/or the treatment of surface albedo was modified. While
this alleviated some of the model biases in snow-off dates, 2 m
temperature and surface albedo, especially the early bias in
snow-off in the western parts of northern Eurasia proved very
robust and was actually larger in the nudged runs.
A key issue underlying the snow-off biases in ECHAM5 is that snowmelt occurs at too low temperatures. Very likely, this is related to
the treatment of the surface energy budget. On one hand, the surface
temperature Ts is not computed separately for the
snow-covered and snow-free parts of the grid cells, which prevents
Ts from rising above 0 °C before all snow
has vanished. Consequently, too much of the surface net radiation is
consumed in melting snow and too little in heating the air. On the
other hand, ECHAM5 does not include a canopy layer. Thus, while the
albedo reduction due to canopy is accounted for, the shielding of
snow on ground by the overlying canopy is not considered, which
leaves too much solar radiation available for melting snow. |
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