Geoscience Reference
In-Depth Information
of the present study the upper limit of
β
0
values was chosen from the condition
s
−
2
. As it will be shown below, this approximately corresponds to
1-10% of the energy of a strong earthquake, if it is uniformly distributed over the
water column over the pleistoseismic zone. The maximum scale of turbulent mo-
tion,
L
, having a natural upper limit equal to the depth
H
, did not exceed 100 m in
calculations. The choice of lower limits for the values of parameters
= 1m
2
β
0
τ
·
β
0
and
L
was
based on the absence of noticeable variations in the initial temperature profile for
times up to 1,000 s.
The main purpose of investigating the system (7.1)-(7.7) consists in determining
the values of parameters
, for which noticeable transformation of the ini-
tial temperature profile occurs. Such a transformation is conveniently traced either
by variation in the surface temperature,
β
0
,
L
and
τ
δ
T
s
, or by variation in the centre-of-mass
position of the water column,
δ
z
.
δ
T
s
=
T
(0
,
t
)
−
T
(0
,
0)
,
δ
z
=(
z
(
t
)
−
z
(0))
,
where
⎛
⎞
−
1
H
H
⎝
⎠
z
(
t
)=
z
ρ
(
z
,
t
) d
z
ρ
(
z
,
t
) d
z
.
0
0
Variation of the centre-of-mass position is a more universal characteristic, since
it permits to trace changes in the density (temperature) profile in such cases, when
these changes do not influence the surface. Moreover, knowledge of the quantity
z
makes it possible to calculate the potential energy of local stratification disruption
(per unit area).
δ
P
=
ρ
0
H
g
δ
z
.
(7.8)
Local disruption of the vertical density distribution should, clearly, become
the source of internal waves, the energy the upper limit of which can be estimated
applying formula (7.8). Probably, the registration of internal waves of precisely such
nature was described in [Filonov (1997)].
Figure 7.5 presents an example of the evolution of temperature and turbulence
energy profiles. Profile
b
(
z
,
0) coincides with axis 0
z
and is not indicated in the
figure. With time, the temperature profile smooths out, and the surface tempera-
ture gradually decreases. The turbulence energy profile exhibits a local minimum in
the region of the thermocline, the existence of which is related to enhanced energy
losses, spent on work against buoyancy forces. As the temperature profile smooths
out, the minimum on profile
b
(
z
) becomes less pronounced.
Figure 7.5 illustrates only one of the two main scenarios for development of
the process in the system investigated. Thus, the first scenario (high-power source
of turbulence) is characterized by a decrease in the maximum temperature gradient
and by significant variations in the surface temperature. In the case of a source of
relatively low power (Fig. 7.6) the maximum temperature gradient monotonously
increases with time, while the surface temperature does not change.
