Geoscience Reference
In-Depth Information
The temperatures are taken in Kelvin-degrees in the calculations. These expressions
look somewhat complicated but the resulting climatological values are rather smooth, with
seasonal variation coming from the solar radiation and the latent heat
fl
flux (Table 4.1 ). In
45 W m 2
15 W m 2
C 1 , while in the summer they are
winter k 0 -
and k 1
°
100 W m 2 and k 1
25 W m 2
C 1 .
k 0
°
4.2
Ice Growth and Melting
4.2.1 Thermodynamic Principles
Whether the surface is snow, ice or liquid water makes a major difference to the albedo,
and in the latent heat transfer sublimation (snow or ice) needs more energy than evapo-
ration (water). Otherwise the same parameters can be used. But in the cold season, the
thicker the ice the closer the surface temperature becomes to air temperature that reduces
turbulent heat transfer.
When an ice cover forms and grows, the stratigraphy may contain three different types
of layers: congelation ice, frazil ice, and superimposed ice (Fig. 4.4 ). On top of the ice
sheet, there is often a snow layer. Each layer grows by its own speci
c mechanism, and
the latent heat released needs to be conducted to the atmosphere, since the water body is
warmer than the ice. The latent heat of freezing is large (333.5 kJ kg 1 ), and therefore ice
growth is slow process (order of 1
flux of 35 W m 2 is released
when ice grows by 1 cm in 24 h. Ice sheet is primarily described by its thickness, which is
de
3 cm day 1 ). The heat
fl
-
ned as the distance between the upper and lower boundaries.
In the melting period, ice sheet is nearly isothermal. There is not much conduction of
heat, and melting takes place at the top and bottom boundaries and by solar radiation also
in the interior. Heat corresponding to the latent heat of freezing must be provided to melt
the ice. Different layers melt by the same mechanisms but there are quantitative differ-
ences depending on the albedo and light attenuation coef
cient. Therefore ice growth is
first treated separately of different ice types, and thereafter melting is discussed together
for all ice types.
Fig. 4.4 A schematic picture
of a vertical cross-section of a
lake ice sheet
 
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