Location
MC 5501
Speaker
Prof. Pete Diamessis, Cornell University
Title
Formation and evolution of turbulence in convectively unstable internal solitary waves of depression shoaling over gentle slopes
Abstract
The shoaling of high-amplitude Internal Solitary Waves (ISWs) of depression over gentle slopes is examined through large-scale parallel turbulence-resolving high-accuracy/resolution simulations. A select, near-isobath-normal, bathymetric transect of the gentle continental slope from the South China Sea, a global hotbed of high-amplitude ISWs, is employed together with stratification and current profiles obtained by in-situ measurements. Three simulations of separate ISWs with initial deep-water amplitudes in the range [136m, 150m] leverage a novel wave-tracking capability for a propagation distance of 80km and accurately reproduce key features of in-situ-observed phenomena with significantly higher spatiotemporal resolution. The interplay between convective and shear instability and the associated turbulence formation and evolution are further studied, as a function of deep-water ISW amplitude, in-part revealing processes previously not observed in the field. Across all three waves, the convective instability develops in a similar fashion: heavier water entrained from the wave rear plunges into its interior, giving rise to transient, yet distinct, subsurface vortical structures which transition to turbulence. Ultimately, a distinct frontal feature is established which horizontally advances through the wave interior and mixes it down to the pycnocline base. Although the waveform remains distinctly symmetric, Kelvin-Helmholtz billows emerge near the well-mixed ISW trough, disturb the wave’s trailing edge and give rise to an active wake. The wake's perturbation kinetic energy can become a sizable fraction of the kinetic energy of the deep-water ISW, suggesting the wake is a primary mechanism of water column mixing.The concluding segment of the talk will revolve around a discussion of the sensitivity of these simulations to choice of computational domain width, as increased by a factor of 4x and 16x with respect to the baseline set-up. Emphasis will be placed on the novel large lateral actively overturning events which emerge and can more effectively mix the ISW base while interacting nonlinearly to produce very-large-scale ejection events out of the ISW rear.
This event is part of the NSERC CREATE-funded Quantitative Climate Science program. More information about this initiative can be found at https://qcs-create2024.github.io/