CASPO Seminar: Drew Lucas (SIO and MAE), "The phenomenology of internal gravity wave evolution in the internal surf zone"

05/09/2018 - 3:30pm


Internal waves play a first-order role in the energetics, property exchange, and biogeochemistry of the ocean. This is particularly true of our local coastal waters, where internal waves drive much of the sub-seasonal and shorter time-scale mixing and thus power local ecosystems. In this talk, I will present first-of-their-kind observations of the internal wave field offshore of SIO, collected with a fiber optic distributed temperature sensing system and wave-powered profiling vehicles. The measurements allow a coherent view of the cascade of variability from the relatively large scale internal tide to the shoaling and dissipation of individual internal solitary- like waves over the mid and inner-shelf. I’ll discuss the role La Jolla Canyon plays in the breakdown of the internal tide to both turbulence and higher frequency internal waves. I’ll also show that the modulation of the inner shelf wave-guide by the internal tide influences the evolution of trains of shoaling nonlinear solitary-like waves. Specifically, pycnocline-sharpening strain due to the internal tide causes 1) the solitary wave polarity transition zone to shrink to a horizontal scale similar to that of the impinging waves, and 2) the impinging waves to have amplitudes exceeding the extended-KdV limiting value. When these conditions are met, the shoaling waves are destroyed through the generation of a back-radiating dispersive wave tail, and not simply mixing in the wave core or convective breaking. The observation of this offshore propagating unsteady wave-tail is unique, and implies that, for many stratifications and continental shelf slopes, similar processes may control the transfer of energy from the internal wave field to mixing. 

For more information on this event, contact: 
Theresa Morrison
Event Calendar: 
Nierenberg Hall 101