vertical turbulent plumes at the stratification consisting of a linearly stratified layer
over a homogeneous layer. Ezhova et al. [24] performed a numerical experiment
with a turbulent jet at the stratification with a pycnocline of a finite thickness. Two
different pycnocline thicknesses have been considered, one is a narrow pycnocline
as compared to the plume diameter in the pycnocline and another one is a wider
pycnocline equal to the plume diameter. The frequencies of jet oscillations in
different pycnoclines were remarkably similar, while the IW frequencies depended
on the ambient stratification. However, peaks in the spectra of IW coincided with
the spectra of plume oscillations (when the peaks in the spectra of jet oscillations
were lower than the maximum buoyancy frequency). Another numerical investigation by Ezhova et al. (submitted) considers buoyant plumes in a stratified fluid
with the complex stratification: weakly linear with a pycnocline of a finite width,
modeling subglacial discharge in the Greenland fjords. Plume oscillations at
complicated stratifications result in noisier spectra. The peaks can be still detected
when the stratification resembles two layers separated by a pycnocline, while the
measurements at stratifications more similar to that reported by Ansong and
Sutherland (1990) show correspondence with their results.
Structure and Energetics of Internal Waves
The structure of internal waves generated by the vertical turbulent plumes in a
two-layer stratification with a pycnocline of finite thickness were investigated in
detail by Bondur et al. [11, 12]. The work describes the results of laboratory scale
modeling of submerged wastewater outfalls in the LTST (see Fig. 7) and the corresponding theoretical analysis. Experimental measurements were performed using
an antenna of thermistors located at a significant distance from the collector model
in the thermocline (approximately a dozen of plume diameters measured at the
inflow of the plume to the pycnocline) (Fig. 10).
The antenna was located vertically in the thermocline, thus measuring temperature at several fixed points in the vertical direction (see the description of the
experiment in section “Introduction”). The isotherms corresponding to different
fixed temperatures were retrieved from the collected data and the spectra of isotherm displacements from the equilibrium depth were assumed as the spectra of IW.
As mentioned in in section, “Genaration of Internal Waves by Turbulent Buoyant
Plumes” all spectra, regardless the outflow velocity, have a pronounced peak close
to 0.6–0.7 N_max, where N_max is the maximal buoyancy frequency (Figs. 11).
The vertical buoyant plume penetrates through the pycnocline, then bounces
back and propagates horizontally as a gravity current at the level of the neutral
buoyancy. The velocity of the gravity current in the thermocline was measured in
the above mentioned experiments by a three-component Doppler velocity profiler.
These measurements allowed us to develop a theoretical model of internal waves
based on the mean temperature profile with the account for the horizontal flow in
the thermocline. The velocities of these horizontal flows are comparable with the
76
V. G. Bondur et al.
over a homogeneous layer. Ezhova et al. [24] performed a numerical experiment
with a turbulent jet at the stratification with a pycnocline of a finite thickness. Two
different pycnocline thicknesses have been considered, one is a narrow pycnocline
as compared to the plume diameter in the pycnocline and another one is a wider
pycnocline equal to the plume diameter. The frequencies of jet oscillations in
different pycnoclines were remarkably similar, while the IW frequencies depended
on the ambient stratification. However, peaks in the spectra of IW coincided with
the spectra of plume oscillations (when the peaks in the spectra of jet oscillations
were lower than the maximum buoyancy frequency). Another numerical investigation by Ezhova et al. (submitted) considers buoyant plumes in a stratified fluid
with the complex stratification: weakly linear with a pycnocline of a finite width,
modeling subglacial discharge in the Greenland fjords. Plume oscillations at
complicated stratifications result in noisier spectra. The peaks can be still detected
when the stratification resembles two layers separated by a pycnocline, while the
measurements at stratifications more similar to that reported by Ansong and
Sutherland (1990) show correspondence with their results.
Structure and Energetics of Internal Waves
The structure of internal waves generated by the vertical turbulent plumes in a
two-layer stratification with a pycnocline of finite thickness were investigated in
detail by Bondur et al. [11, 12]. The work describes the results of laboratory scale
modeling of submerged wastewater outfalls in the LTST (see Fig. 7) and the corresponding theoretical analysis. Experimental measurements were performed using
an antenna of thermistors located at a significant distance from the collector model
in the thermocline (approximately a dozen of plume diameters measured at the
inflow of the plume to the pycnocline) (Fig. 10).
The antenna was located vertically in the thermocline, thus measuring temperature at several fixed points in the vertical direction (see the description of the
experiment in section “Introduction”). The isotherms corresponding to different
fixed temperatures were retrieved from the collected data and the spectra of isotherm displacements from the equilibrium depth were assumed as the spectra of IW.
As mentioned in in section, “Genaration of Internal Waves by Turbulent Buoyant
Plumes” all spectra, regardless the outflow velocity, have a pronounced peak close
to 0.6–0.7 N_max, where N_max is the maximal buoyancy frequency (Figs. 11).
The vertical buoyant plume penetrates through the pycnocline, then bounces
back and propagates horizontally as a gravity current at the level of the neutral
buoyancy. The velocity of the gravity current in the thermocline was measured in
the above mentioned experiments by a three-component Doppler velocity profiler.
These measurements allowed us to develop a theoretical model of internal waves
based on the mean temperature profile with the account for the horizontal flow in
the thermocline. The velocities of these horizontal flows are comparable with the
76
V. G. Bondur et al.