P. Bouruetaubertot et al., STRATIFIED TURBULENCE PRODUCED BY INTERNAL WAVE BREAKING - 2-DIMENSIONAL NUMERICAL EXPERIMENTS, Dynamics of atmospheres and oceans, 23(1-4), 1996, pp. 357-369
In an earlier study (Bouruet-Aubertot et al., J. Fluid Mech., 285: 265
-301, 1995) the evolution of a large-scale, high-frequency, standing i
nternal gravity wave was investigated by means of two-dimensional nume
rical computations. It was shown that breaking eventually occurs, what
ever the wave amplitude. The instability mechanisms leading to breakin
g were analysed in detail. In the present paper, we study the strongly
nonlinear regime resulting from wave breaking. Buoyancy and velocity
variance spectra display a wavenumber range scaling as 0.2N(2)k(y)(-3)
and 0.1N(2)k(y)(-3), respectively (N being the Brunt-Vaisala frequenc
y and ky the vertical wavenumber). The buoyancy variance spectrum has
the same power law and level as in a laboratory experiment performed o
n the same subject by Benielli and Sommeria (Dyn. Atmos. Oceans, 23: 3
35-343, 1996), and is very close to fine-scale oceanic temperature spe
ctra, The buoyancy flux spectrum appears to be counter-gradient at sma
ll scales, confirming results from previously published numerical simu
lations. We propose a physical interpretation for this small-scale beh
aviour. Finally, the spectrum of the buoyancy flux is compared with th
e kinetic energy and buoyancy variance spectra, to quantify its role i
n energy transfers. This point is essential for deciding between the t
heories proposed to explain the k(-3) spectral range, which is also ob
served in the stratosphere.