Local turbulence and baroclinic energy balance in a Luzon Strait model

Masoud Jalali1, Sutanu Sarkar1 and Vamsi K Chalamalla2, (1)University of California San Diego, La Jolla, CA, United States, (2)University of California at San Diego, Aerospace and Mechanical Engineering, San Diego, CA
Abstract:
Generation sites for topographic internal gravity waves can also be sites of intense turbulence. The present work uses high resolution 3D LES to simulate flow over a model with topography patterned after a cross-section of Luzon Strait at latitude of $20.6^{\circ}$, double-ridge generation site which was the subject of the recent IWISE experiment. The west ridge has been modeled in isolation, and at 1:100 length scale using environmental parameters that match important nondimensional numbers such as the slope criticality, Froude number, and Excursion number. Comparison with observations at measurement station N2 shows generally good agreement with the amplitude and phasing of velocity, overturns and turbulent dissipation except for the lack of resonance with the east ridge at a specific tidal phase. Bc-Bt energy conversion equation terms are calculated and the budget is closed. The results emphasize the importance of turbulent processes with the local energy loss, $q \simeq 35\%$.
Several turbulent mechanisms are found to be responsible for turbulence including breaking lee waves during flow reversal and downslope jets that have been observed (Alford et al. (2011), Alford et al. (2015)) as well as critical slope boundary layer, internal wave beams, off-slope lee wave breaking and valley flows. Wave breaking and turbulence at these sub-ridges are governed by an inner Excursion number ($Ex_{in}$) and exhibit similarity with the regimes identified by DNS of Jalali et al. (2014).
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