Internal water circulation depends on thermal stratification [13] because an internal interface is required for internal wave motions to occur. Internal waves are the driving force for horizontal and vertical fluxes at basin-scale [6]. It has been shown that most of the momentum (90%) and energy that passes through the epilimnion and excites the thermocline is transferred to basin-scale internal wave motions. The remaining energy (about 10% of the total wind energy) is transformed to small-scale turbulence that induces mixing. The energy is mainly dissipated by bottom shear from seiche currents and periodic breaking of internal waves on the slopping lake bed. A small portion of the energy is dissipated by shear instabilities of internal waves breaking [5].
The main drivers for the internal waves are variations in wind stress, residual circulation induced by bathymetry interaction, changes in density in the water column and the Earth’s rotation [10]. The periods of the internal waves in Lake Ontario range from a few hours to several days. If Earth's rotation is not considered they have a sinusoidal in shape in the direction of propagation and their nodes correspond to lines of zero isotherm surface displacement [7]. Internal progressive waves motions are similar to surface wave motions, but have larger amplitudes and periods and are considered very influential in the transport of heat and other properties through the thermocline [6].
Internal waves dissipate most energy by overturning or shear instability, however, other mechanisms such as viscous attenuation, distortion, wave-wave interaction and interaction with bottom are also important [7].