Thermodynamics of Seasonal Lake Ice - Freezing of Lakes and the Evolution of their Ice Cover - page 135

Fig. 4.15 A two-phase model
outcome. The lines show
evolution of ice porosity in the
ice cover, peaking at 10 - 15 cm
depth

Porosity (%)

0 10 20 30 40 50

5

10

15

20

25

30

q I ¼ @
@ z

j @ T

@ z Q s

ð 4 : 66d Þ

The boundary conditions are similar to those in the classical models and positive
boundary heating decreases the thickness of ice. Absorption of sunlight decreases with
depth but surface heat balance tends to be negative due to terrestrial radiation losses and
sublimation. As a result, the porosity will have a maximum beneath the surface, typically
at 10 20 cm depth (Fig. 4.15 ).

In the two-phase model slush layers are well reproduced and the physical represen-
tation of melting ice is realistic. Also a mechanical model can be added to examine the
breakage of ice, which is a critically important factor to the character of lake ice seasons.
Mechanical problems have not been much discussed in the lake ice seasonal models,
although mechanical events are thickness and ice quality dependent and therefore sensi-
tive to climate variations. If the modelled ice structure evaluation is correct, better esti-
mates for ice loads and bearing capacity are obtained, ice breakup comes correctly, and
realistic locations of biological habitats are seen in the ice sheet.

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