Masoud Jalali

On the Accuracy of Overturn-Based Estimates of Turbulent Dissipation at Rough Topography

AbstractEvidence in support of overturn-based methods, often used to infer turbulent dissipation rate from density profiles, is typically from regions with weaker turbulence than that at rough-topography hotspots. The present work uses direct numerical simulations (DNS) of an idealized problem of sloping topography as well as high-resolution large-eddy simulation (LES) of turbulent flow at more realistic topography in order to investigate the accuracy of overturn-based methods in sites with internal wave breaking. Two methods are assessed: Thorpe sorting, where the overturn length LT is based on local distortion of measured density from the background, and inversion sorting, where the inversion length scale LI measures the statically unstable local region. The overturn boundaries are different between the two methods. Thorpe sorting leads to an order of magnitude overestimate of the turbulent dissipation in the DNS during large convective overturn events when inversion sorting is more accurate. The LES of...

Large Eddy Simulation of Flow and Turbulence at the Steep Topography of Luzon Strait

Steep generation sites for topographic internal gravity waves can also be sites of turbulence. The present work uses turbulence-resolving Large Eddy Simulation (LES) for tidal flow over multiscale, steep bathymetry patterned after a portion of the west ridge of Luzon Strait at 20.6∘ N. Oceanic values of the slope criticality, Froude number, excursion number, and aspect ratio are matched. The amplitude and phasing of velocity, overturns, and dissipation are similar to observations made at a deep mooring. However a tidal phase is noted in which there is a discrepancy that could arise from the resonant interaction with waves generated at the east ridge that is not included in the model. Turbulent dissipation originates from several mechanisms including breaking lee waves during flow reversal, downslope jets, critical-slope boundary layer, high-mode internal wave beams, off-slope lee wave breaking and wave breaking in a valley between subridges. The model baroclinic energy budget is closed with negligible residual and the local turbulence loss of 23.5% is large.