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oscillations (Petrov et al. 2007). In Lake Baikal the
fl
flow velocities produced by seiches
2cms 1 with periods of 280 min (Zhdanov et al. 2001).
Ice-covered lakes have normally a stable strati
amount up to 1
-
cation, and therefore they are also able
to give a baroclinic response to external forcing (see Kirillin et al. 2012). By analogy with
the barotropic oscillations, the length scale for the internal seiches is expressed by the
internal Rossby radius
L i ¼ c i f 1
ð
7
:
25
Þ
where c i is the internal wave speed. For an idealized case of a two-layered
fl
fluid with layer
thicknesses h 1 and h 2 and a density difference
ʔρ
between them, the wave speed c i is
given by
s
g D q
q h 1 h 2
c i ¼
ð
7
:
26
Þ
h 1 þ h 2
For the density ratio of 10 2 and h 1 *
0.3 m s 1 . If the
1m,h 1 *
9 m, we have c i *
strati
cation is continuous with a constant density gradient
ʔρ
/
ʗ
across the lake depth,
Eq. ( 7.26 ) turns into
s
g
H
D q
q 0
c i ¼ p NH ¼ p
ð
7
:
27
Þ
frequency. With the density ratio of 10 2 and lake depth of 10 m,
where N is the V
ä
is
ä
l
ä
frequency is 0.099 s 1 and, consequently, ci i *
0.3 m s 1 .
V
ä
is
ä
l
ä
cation in ice-covered freshwater lakes is relatively weak, limited by the
temperature difference Tf. m
Density strati
T f . Therefore c i
c, and the baroclinic Rossby radius of
deformation is Li i *
s
rotation plays an important role in baroclinic motions in even medium-size lakes. In the
majority of ice-covered lakes, baroclinic waves are strongly in
5 km, in weakly strati
ed lakes even less than that. Thus Earth
'
uenced by the Coriolis
acceleration and their dynamics resemble oceanic conditions rather than those in the same
lakes in summer.
A thin (0.1
fl
cantly
warmer than the bulk water body, with high concentration of dissolved matter and high
mixing rates produced by density currents and internal seiches (Malm 1999; Petrov et al.
2007; Kirillin et al. 2012b). This layer has also a high content of nutrients. Shear insta-
bilities, produced by the density currents, and breaking of internal waves at the horizontal
density interfaces are the major sources of mixing.
Periodic variations of the temperature
1.0 m) layer is formed in the very vicinity of the lake bottom, signi
-
field associated with large-scale internal waves
have been registered in ice-covered lakes (Petrov et al. 2006; Kirillin et al. 2009;
Zdorovennova 2009). Affected by the Earth ' s rotation, these oscillations take the form of
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