Effect of the shear flow in the generation and self-organization of internal gravity wave structures in the dissipative ionosphere

2012 ◽  
Vol 38 (12) ◽  
pp. 972-990 ◽  
Author(s):  
G. D. Aburjania ◽  
G. Zimbardo ◽  
O. A. Kharshiladze
Keyword(s):  
Shear Flow ◽  
Gravity Wave ◽  
Internal Gravity Wave ◽  
Self Organization

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.

Vorticity dynamics in a breaking internal gravity wave. Part 1. Initial instability evolution

1998 ◽  
Vol 367 ◽  
pp. 27-46 ◽  
Author(s):  
ØYVIND ANDREASSEN ◽  
PER ØYVIND HVIDSTEN ◽  
DAVID C. FRITTS ◽  
STEVE ARENDT
Keyword(s):  
Shear Flow ◽  
Gravity Wave ◽  
Three Dimensional ◽  
Internal Gravity Wave ◽  
Companion Paper ◽  
Vortex Sheets ◽  
Vortex Loops ◽  
Vorticity Dynamics ◽  
Spanwise Vorticity ◽  
Dimensional Simulation

A three-dimensional simulation of a breaking internal gravity wave in a stratified, compressible, sheared fluid is used to examine the vorticity dynamics accompanying the transition from laminar to turbulent flow. Our results show that baroclinic sources contribute preferentially to eddy vorticity generation during the initial convective instability of the wave field; the resulting counter-rotating vortices are aligned with the external shear flow. These vortices enhance the spanwise vorticity of the shear flow via stretching and distort the spanwise vorticity via advective tilting. The resulting vortex sheets undergo a dynamical (Kelvin–Helmholtz) instability which rolls the vortex sheets into tubes. These vortex tubes link with the original streamwise convective rolls to produce a collection of intertwined vortex loops. A companion paper (Part 2) describes the subsequent interactions among and the perturbations to these vortices that drive the evolution toward turbulence and smaller scales of motion.

Mean flows induced by internal gravity wave packets propagating in a shear flow

1979 ◽  
Vol 292 (1393) ◽  
pp. 391-417 ◽  
Keyword(s):  
Shear Flow ◽  
Gravity Wave ◽  
Internal Gravity Wave ◽  
Basic Flow ◽  
Channel Depth ◽  
Amplitude Wave ◽  
Generalized Lagrangian ◽  
Basic Shear ◽  
Wave Induced ◽  
The Waves

An inviscid, incompressible, stably stratified fluid occupies a horizontal channel, along which an internal gravity wave packet is propagating in the presence of a basic shear flow. By using a generalized Lagrangian mean formulation, the equation for wave action conservation is derived to describe the manner in which the basic flow affects the waves. Equations describing the second-order (in amplitude) wave-induced Lagrangian mean flows are obtained. Two kinds of applications are discussed: (i) steady mean flows, due to waves encountering an inhomogeneity in their environment, such as a varying channel depth; (ii) mean flows induced by modulations in the wave amplitude.

On parametric instabilities of finite-amplitude internal gravity waves

1982 ◽  
Vol 119 ◽  
pp. 367-377 ◽  
Author(s):  
J. Klostermeyer
Keyword(s):  
Gravity Wave ◽  
Internal Gravity Wave ◽  
Maximum Growth ◽  
Numerical Approach ◽  
Internal Gravity Waves ◽  
Resonant Interaction ◽  
Finite Amplitude ◽  
Interaction Diagram ◽  
Parametric Instabilities ◽  
Boussinesq Fluid

The equations describing parametric instabilities of a finite-amplitude internal gravity wave in an inviscid Boussinesq fluid are studied numerically. By improving the numerical approach, discarding the concept of spurious roots and considering the whole range of directions of the Floquet vector, Mied's work is generalized to its full complexity. In the limit of large disturbance wavenumbers, the unstable disturbances propagate in the directions of the two infinite curve segments of the related resonant-interaction diagram. They can therefore be classified into two families which are characterized by special propagation directions. At high wavenumbers the maximum growth rates converge to limits which do not depend on the direction of the Floquet vector. The limits are different for both families; the disturbance waves propagating at the smaller angle to the basic gravity wave grow at the larger rate.

scholarly journals Momentum and Energy Transport by Gravity Waves in Stochastically Driven Stratified Flows. Part I: Radiation of Gravity Waves from a Shear Layer

2007 ◽  
Vol 64 (5) ◽  
pp. 1509-1529 ◽  
Author(s):  
Nikolaos A. Bakas ◽  
Petros J. Ioannou
Keyword(s):  
Shear Flow ◽  
Shear Layer ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Wave Energy ◽  
Energy Transport ◽  
Wave Spectrum ◽  
Internal Gravity Waves ◽  
Wave Interference ◽  
Wide Range

Abstract In this paper, the emission of internal gravity waves from a local westerly shear layer is studied. Thermal and/or vorticity forcing of the shear layer with a wide range of frequencies and scales can lead to strong emission of gravity waves in the region exterior to the shear layer. The shear flow not only passively filters and refracts the emitted wave spectrum, but also actively participates in the gravity wave emission in conjunction with the distributed forcing. This interaction leads to enhanced radiated momentum fluxes but more importantly to enhanced gravity wave energy fluxes. This enhanced emission power can be traced to the nonnormal growth of the perturbations in the shear region, that is, to the transfer of the kinetic energy of the mean shear flow to the emitted gravity waves. The emitted wave energy flux increases with shear and can become as large as 30 times greater than the corresponding flux emitted in the absence of a localized shear region. Waves that have horizontal wavelengths larger than the depth of the shear layer radiate easterly momentum away, whereas the shorter waves are trapped in the shear region and deposit their momentum at their critical levels. The observed spectrum, as well as the physical mechanisms influencing the spectrum such as wave interference and Doppler shifting effects, is discussed. While for large Richardson numbers there is equipartition of momentum among a wide range of frequencies, most of the energy is found to be carried by waves having vertical wavelengths in a narrow band around the value of twice the depth of the region. It is shown that the waves that are emitted from the shear region have vertical wavelengths of the size of the shear region.

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