Internal gravity waves in a dipolar wind: a wave–vortex interaction experiment in a stratified fluid

Abstract

An experimental study on the interaction of the internal wave field generated by oscillating cylinders in a stratified fluid with a pancake dipole is presented. The experiments are carried out in a salt-stratified water tank with constant Brunt-Väisälä frequency (N). Experimental observations of the deformation of the wave beams owing to the interaction with the dipole are presented. When the wave and the dipole propagate horizontally in opposite directions (counterpropagating case), the phase line of the gravity wave beam steepens towards the vertical as it enters the dipolar field and it may even reach a turning point where the wave is reflected. When the dipole and the wave propagate in the same direction (copropagating case), the wave beam is bent towards the horizontal and may be absorbed by the dipole. These observations are in good agreement with a two-dimensional ray-theoretic model, even if the flow is fully three-dimensional and, the vertical shear induced by the dipole being too strong, the hypothesis of slow variation assumed in the WKB approximation is not verified. When the waves encounter a critical layer, we show by rigorous measurement that momentum is transferred to the dipole. New three-dimensional effects of the dipolar velocity field on the propagating internal waves are also discussed. In particular, focusing and refraction of a wave beam occurring because of the horizontal structure of the background dipolar flow allow us to explain some of the observed features that cannot be accounted for through the two-dimensional ray theory.

Characteristics of Submeso Winds in the Stable Boundary Layer

“…More definite conclusions must await more dense networks. Measurements of vertical structure would be required to examine the interaction between gravity waves and two-dimensional vorticies, as observed in laboratory flows (Godoy-Diana et al 2006).…”

“…Based on numerical studies, laboratory experiments and theoretical considerations, the submeso modes in stratified flow are viewed as a combination of gravity waves and horizontal modes, sometimes referred to as pancake vortices (see, for example, Riley and Lelong 2000;Waite and Bartello 2004;Meunier et al 2005, and references therein). Interaction between the gravity waves and two-dimensional modes are explored by Godoy-Diana et al (2006), and interaction between turbulence, submeso motions and drainage flows was demonstrated by Monti et al (2002). Horizontal modes have been difficult to identify from atmospheric data, perhaps due to inadequacy of the datasets.…”

Investigation of High-Frequency Internal Wave Interactions with an Enveloped Inertia Wave

“…Several various mechanisms may lead to internal waves shifting or refracting to higher frequency and steepening, eventually leading to wave breaking. These include high-frequency wave-wave interactions [24,25], high-lowfrequency wave interactions [26][27][28][29][30][31], wave-vortex interactions [32], self-acceleration [33,34], and wave steepening due to propagation through a shear [35][36][37].…”

Vortex Rossby waves in mesoscale dipoles

“…To mention just a few, some have addressed the dipole formation [ van Heijst and Flór , 1989; Mied et al , 1991; Spall and Robinson , 1990; Kloosterziel and van Heijst , 1991; Spall , 1995; Orlandi and Carnevale , 1999; Sansón et al , 2001; Feng et al , 2007], the dipole structure [ Norbury , 1973; Fedorov and Ginsburg , 1986; Couder and Basdevant , 1986; Sheres and Kenyon , 1989; Simpson and Lynn , 1990; Carton , 2001], and dipole dynamics [ Pierrehumbert , 1980; Rasmussen et al , 1996; Eames and Flór , 1998; Kizner et al , 2003; Pallàs‐Sanz and Viúdez , 2007]. Other investigations have focused on their interaction, namely dipole‐dipole interaction [ McWilliams and Zabusky , 1982; van Heijst and Flór , 1989; Velasco Fuentes and van Heijst , 1995; Dubosq and Viúdez , 2007], dipole‐topography interaction [ Kloosterziel et al , 1993; Carnevale et al , 1997], and dipole‐wave interaction [ Godoy‐Diana et al , 2006].…”