Geoscience Reference
In-Depth Information
of heights of the column of liquid. This fact opens up the possibility of using the ob-
tained results in studying seaquakes, arising in the case of underwater earthquakes
or other local perturbations of the ocean bottom. The results of the experiment are
relevant to shallow areas of the ocean or to its upper layer. The mechanisms of tur-
bulence generation in the ocean column in the case of underwater earthquakes are,
most probably, of another nature.
The vertical exchange intensity in a liquid column in the case of a section of
the bottom undergoing oscillations was estimated by the transformation of verti-
cal temperature profiles. Processing of the temperature profiles was performed in
accordance with the formula
⎛
⎞
z
=0
z
1
∂
∂
T
∂
d
z
+
K
0
∂
T
∂
⎝
⎠
K
(
z
)=
(7.21)
T
t
z
0
∂
z
The quantity
K
0
was chosen to be the molecular coefficient of temperature con-
ductivity of water, equal to 0.0014 cm
2
s
−
1
.
In Fig. 7.18 the examples are presented of successively measured temperature
profiles and of the respectively calculated profiles of the vertical turbulent exchange
coefficient. The two presented cases correspond to weak (close to molecular) and
intense turbulent exchange at bottom oscillation frequencies of 3.4 and 39.5 Hz,
respectively.
For a quantitative analysis it is necessary to have a scalar quantitative character-
istic, reflecting the vertical exchange intensities. Significant (more than an order of
magnitude) variations of the quantity
K
(
z
) over the ocean depth make simple av-
eraging of this coefficient over the depth unacceptable. It has been noted that most
profiles of the turbulent exchange coefficient expressed in semilogarithmic coordi-
nates (
z
,
ln
K
) are described not badly by a linear dependence. In this connection,
their exponential approximation was constructed in the form
K
(
z
)=
C
0
exp
{
α
z
}
(7.22)
The coefficients of approximation (7.22) were determined by the method of least
squares for a group of profiles obtained during a single experiment for fixed fre-
quencies and amplitudes of bottom oscillations. Then, the constructed regression
dependence was applied for calculating the turbulent exchange coefficient close to
the water surface (at point
z
= 7 cm). The error in the estimate of
K
(7) was deter-
mined in the standard way.
Figure 7.19 presents, in a double logarithmic scale, values of the turbulent ex-
change coefficient
K
(7) versus the acceleration amplitude of bottom oscillations,
corresponding to different oscillation frequencies and amplitudes. The
K
(7) values
are normalized to the molecular coefficient of temperature conductivity in water,
K
0
, and the acceleration amplitude is normalized to the free-fall acceleration. From
the figure it is seen that right up to acceleration amplitudes of about 0
.
2 g (i.e. before
the rise moment of structures), independently of the piston's oscillation amplitude,
