Physical Oceanography, Vol.
6, March, 2012 (Ukrainian Original No.
6, November–December, 2011)
DISSIPATION OF ENERGY AND VERTICAL EXCHANGE IN STRATIFIED BASINS
CAUSED BY THE SHEAR INSTABILITY IN THE FIELD OF QUASIINERTIAL
A. S. Samodurov
and L. V. Globina
We determine the dependences of the rate of dissipation of turbulent energy and the coefficient of verti-
cal turbulent diffusion caused by the shear instability and breaking in the field of inertial gravity internal
waves in the ocean on the local buoyancy frequency. Within the framework of a unified approach, we
explain the difference between these dependences observed for the areas of the main pycnocline and the
upper stratified layer and mentioned in the literature. The indicated difference is explained by the fact
that, unlike the region of the main pycnocline, the characteristic vertical scale of the instability of waves
in the upper stratified layer depends on stratification. The analysis is performed on the basis of the mo-
del of climatic spectrum of internal waves in the ocean proposed by the authors somewhat earlier.
Keywords: internal waves, dissipation of turbulent energy, turbulent diffusion, stratified layers.
The natural stratified basins suffer the action of numerous physical mechanisms capable of affecting the in-
tensity of vertical fluxes of heat, salt, and other dissolved chemical substances. Among these mechanisms, we
can mention density convection, shear instability of stratified currents, various manifestations of double-
diffusive convection, bottom friction, bottom geothermal fluxes, etc. At the same time in the main column of
the stably stratified ocean far from coasts and sharp frontal zones in the open parts of oceans and seas, the main
role in the support of vertical turbulent diffusion is played, most likely, by internal waves . The processes of
generation and evolution, as well as the linear and nonlinear interactions in the field of internal waves, are re-
sponsible for the formation of shear instability (spontaneous both in space and in time) and for the appearance of
turbulent spots. The total effect of the local manifestations of instability can be described as mixing of the strati-
fied fluid as a result of the dissipation of wave energy and preservation of the vertical exchange.
In view of the outlined mechanism of turbulent diffusion, the stratification observed in the water column of
a natural basin can be split into two types. The first type includes the specific features of stratification in the
main pycnocline, where the Väisälä–Brunt frequency
gradually varies with depth. The second type of stra-
tification is observed in the upper stratified layer and characterized by relatively rapid variations of
as a func-
tion of depth (Fig. 1). The causes of this phenomenon are discussed in what follows in detail. They are con-
nected with the fact that, in the present work, we consider unstable inertial gravity internal waves in the ray ap-
proximation  as the main mechanism of mixing and energy dissipation. As the main tool in our investiga-
tions, we use the spectral approach developed in [3, 4].
Marine Hydrophysical Institute, Ukrainian National Academy of Sciences, Sevastopol, Ukraine.
Corresponding author; e-mail: email@example.com.
Translated from Morskoi Gidrofizicheskii Zhurnal, No.
16–27, November–December, 2011. Original article submitted September
17, 2010; revision submitted November 10, 2010.
0928–5105/12/2106–0383 © 2012 Springer Science+Business Media, Inc. 383