Internal gravity waves

Just as surface waves may be excited by a bobbing object at a free surface, so may vertically-propagating internal gravity waves (IGW) be generated inside a continuously stratified fluid by the simple harmonic motion of a solid body, or, through a change of reference frame, the time periodic (e.g. tidal) sloshing of stratified fluid over fixed topography (e.g. the Mid-Atlantic Ridge). IGW may also be excited by gravity current or intrusion flow, thermal forcing associated with latent heat release within convective atmospheric storms, the impingement of Langmuir cells on the ocean thermocline, etc. They are recognized to play a critical role in the transport of nutrients and momentum in the natural environment and are associated, directly or indirectly, with phenomena as varied as clear air turbulence and the return of cold abyssal water to the ocean surface.

Collaborating with Tom Peacock (MIT), Bruce R. Sutherland (Univ. of Alberta) and others, I have examined wave excitation by solid oscillating bodies such as spheres or two-dimensional ridges. In large part, the research objective is to validate theoretical models by comparison against experimental measurement. In the latter case, IGW are visualized using particle image velocimetry or novel optical techniques such as Synthetic Schlieren, developed by Stuart B. Dalziel (Univ. of Cambridge), Bruce R. Sutherland and co-workers. I have also studied IGW generation from intrusions as a possible additional mechanism for wave generation by energetic tropical storms.

The generation of internal gravity waves from an idealized two-dimensional Gaussian ridge. (a) Experiment (PIV); (b) theory (as determined by modifying the theory of Petrelis et al. J. Phys. Oceanogr. 36, 2006). [Figure adapted from Echeverri et al., J. Fluid Mech., 636, 2009]



Recent (and not-so-recent) publications:
  • Modal decomposition of polychromatic internal wave fields in arbitrary stratifications (Wave Motion 95, with A.K. Kaminski) (link)
  • Low-mode internal tide generation by topography: an experimental and numerical investigation (J. Fluid Mech. 636, with P. Echeverri, T. Peacock and K.B. Winters) (link)
  • Internal wave excitation from a collapsing mixed region (Deep-Sea Res. II 51, with B. R. Sutherland and K. Dohan) (link)
  • Intrusive gravity currents and internal gravity wave generation in stratified fluid (J. Fluid Mech. 514, with B.R. Sutherland) (link)
  • Internal wave excitation by a vertically oscillating sphere (J. Fluid Mech. 494, with B.R. Sutherland and K. Onu) (link)