Communication Dans Un Congrès Année : 1998

The structure of internal wave beams

Résumé

Linear monochromatic internal gravity waves in uniformly stratified fluids propagate away from their source along beams inclined at a given angle to the vertical. The inclination $\theta_0$ of the beams is fixed by the ratio of the frequency of oscillation $\omega_0$ to the buoyancy frequency $N$, as $\theta_0 = \arccos(\omega_0/N)$. The resulting wave field has the shape of a St~Andrew's cross in two dimensions, and of a double cone in three dimensions. We apply Green's function methods and asymptotic expansions to the determination of its structure. Waves are described by the generalization of an integral originally derived by Lighthill. Three mechanisms compete to set the structure of the wave field: interference between the waves radiated from the various points of the source; combination of transient waves, generated by the impulsive start of the motion, and steady waves, generated by the subsequent monochromatic forcing; viscous momentum transfer. Depending on the dominant mechanism, the width of the wave beam is either constant, or increases linearly with the distance from the source, or increases as its one-third power, respectively, while the velocity profile takes on a specific shape. Distinct domains of time and space are associated with each mechanism. Their definition, and the transition between them, are all considered.

Résumé-DD98.pdf (66.87 Ko) Télécharger le fichier
Origine Fichiers produits par l'(les) auteur(s)
Licence

Dates et versions

hal-01944459 , version 1 (12-12-2018)

Identifiants

  • HAL Id : hal-01944459 , version 1

Citer

Bruno Voisin. The structure of internal wave beams. International Seminar "Day on Diffraction 98", Jun 1998, St. Petersburg, Russia. ⟨hal-01944459⟩
28 Consultations
92 Téléchargements

Partager

  • More