scholarly journals Flows induced by Coriolis-influenced vertically propagating two-dimensional internal gravity wave packets

2020 ◽  
Vol 5 (6) ◽  
Author(s):  
Bruce R. Sutherland ◽  
Wyatt Reeves ◽  
Ton S. van den Bremer
Keyword(s):  
Gravity Wave ◽  
Wave Packets ◽  
Internal Gravity Wave ◽  
Two Dimensional ◽  
Vertically Propagating

scholarly journals Evolution and Stability of Two-Dimensional Anelastic Internal Gravity Wave Packets

2018 ◽  
Vol 75 (10) ◽  
pp. 3703-3724 ◽  
Author(s):  
Alain D. Gervais ◽  
Gordon E. Swaters ◽  
Ton S. van den Bremer ◽  
Bruce R. Sutherland
Keyword(s):  
Wave Packet ◽  
Gravity Wave ◽  
Linear Theory ◽  
Nonlinear Evolution ◽  
Wave Packets ◽  
Internal Gravity Wave ◽  
Two Dimensional ◽  
Fully Nonlinear ◽  
Weakly Nonlinear ◽  
Nonlinear Simulations

The weakly nonlinear evolution, stability, and overturning of horizontally and vertically localized internal gravity wave packets is examined for a nonrotating, anelastic atmosphere that is stationary in the absence of waves. The weakly nonlinear evolution is examined through the derivation of their wave-induced mean flow, which is used to formulate a nonlinear Schrödinger equation. The induced flow is manifest as a long, hydrostatic, bow wake-like disturbance, whose flow direction transitions from positive on the leading flank of the wave packet to negative on the trailing flank of the wave packet. As such, two-dimensional wave packets are always modulationally unstable. This instability results in enhanced amplitude growth confined to either the leading or trailing flank. Hence, when combined with anelastic growth predicted by linear theory, we anticipate two-dimensional waves will overturn either somewhat below or just above the heights predicted by linear theory. Numerical solutions of the Schrödinger equation are compared with the results of fully nonlinear simulations to establish the validity of the weakly nonlinear theory. Actual wave overturning heights are determined quantitatively from a range of fully nonlinear simulations.

scholarly journals Optimal perturbation growth on a breaking internal gravity wave

2021 ◽  
Vol 925 ◽  
Author(s):  
J.P. Parker ◽  
C.J. Howland ◽  
C.P. Caulfield ◽  
R.R. Kerswell
Keyword(s):  
Shear Flow ◽  
Gravity Wave ◽  
Three Dimensional ◽  
Internal Gravity Wave ◽  
Internal Gravity Waves ◽  
Mixing Efficiency ◽  
Two Dimensional ◽  
Systematic Analysis ◽  
Optimal Perturbation ◽  
Energy Growth

The breaking of internal gravity waves in the abyssal ocean is thought to be responsible for much of the mixing necessary to close oceanic buoyancy budgets. The exact mechanism by which these waves break down into turbulence remains an active area of research and can have significant implications on the mixing efficiency. Recent evidence has suggested that both shear instabilities and convective instabilities play a significant role in the breaking of an internal gravity wave in a high Richardson number mean shear flow. We perform a systematic analysis of the stability of a configuration of an internal gravity wave superimposed on a background shear flow first considered by Howland et al. (J. Fluid Mech., vol. 921, 2021, A24), using direct–adjoint looping to find the perturbation giving maximal energy growth on this evolving flow. We find that three-dimensional, convective mechanisms produce greater energy growth than their two-dimensional counterparts. In particular, we find close agreement with the direct numerical simulations of Howland et al. (J. Fluid Mech., 2021, in press), which demonstrated a clear three-dimensional mechanism causing breakdown to turbulence. The results are shown to hold at realistic Prandtl numbers. At low mean Richardson numbers, two-dimensional, shear-driven mechanisms produce greater energy growth.

Three-dimensional wave instability near a critical level

1994 ◽  
Vol 272 ◽  
pp. 255-284 ◽  
Author(s):  
K. B. Winters ◽  
E. A. D’Asaro
Keyword(s):  
Wave Energy ◽  
Critical Level ◽  
Wave Packets ◽  
Three Dimensional ◽  
Internal Gravity Wave ◽  
Two Dimensional ◽  
Mean Flow ◽  
Wave Instability ◽  
Flow Acceleration ◽  
Dimensional Wave

The behaviour of internal gravity wave packets approaching a critical level is investigated through numerical simulation. Initial-value problems are formulated for both small- and large-amplitude wave packets. Wave propagation and the early stages of interaction with the mean shear are two-dimensional and result in the trapping of wave energy near a critical level. The subsequent dynamics of wave instability, however, are fundamentally different for two- and three-dimensional calculations. Three-dimensionality develops by transverse convective instability of the two-dimensional wave. The initialy two-dimensional flow eventually collapses into quasi-horizontal vortical structures. A detailed energy balance is presented. Of the initial wave energy, roughly one third reflects, one third results in mean flow acceleration and the remainder cascades to small scales where it is dissipated. The detailed budget depends on the wave amplitude, the amount of wave reflection being particularly sensitive.

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