Quantification of energy cascade of internal gravity waves with varying spectral slopes

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Vertical density differences in the ocean support 'internal' waves (waves in the ocean's interior) that have different periods. The energy of these internal waves often trickles down to smaller waves that eventually dissipate, a process known as the energy cascade. The cascade process can lead to mixing, and determines the heat and salt balances and general circulation of the ocean. This project will investigate this energy cascade through theory, modeling, and data analysis. The existing theory of the energy cascade, based on the turbulence produced by internal waves, will be improved in this study (with existing controversies resolved) and extended to more realistic situations. Subsequent validation of the improved theory will be done with high-resolution regional model simulations. The project will also apply this improved theory to a global model simulation and establish a geographic map of dissipation . Broader impacts include enhancements to global climate models and regional models. The theoretical improvement will inform a range of physical applications and mathematical studies of internal wave turbulence. Annual presentations are planned for the turbulence community. The work supports an early career PI, a postdoc, and teaching and public outreach through the Coastal Ocean Environment Summer School in Ghana and public lectures on the history of fluid mechanics through programs at the UM Museum of Natural History.The proposed project will establish a comprehensive understanding of the downscale energy cascade of IGW spectra with variable spectral slopes, from both theoretical and computational considerations. Research tasks include: 1) Development of theoretical formulations of energy cascade for spectra with varying slopes in the wave turbulence theory framework, which will be guided and confirmed by simulations of the kinetic equation. 2) Further improvement of the regional MITgcm simulation of 24-32 degrees N, 193-199 degrees E to better match the spectra from McLane profiler measurements (through adjustment of model resolution and K-profile parameterization), computation of the modeled energy cascade with comparison to theoretical results obtained from task 1. 3) Application of the traditional/new finescale parameterization to a global MITgcm model to establish a geographic map of turbulent dissipation rate, and comparison of the results to those from microstructure measurements. The new finescale parameterization formulation from spectra that more closely match spectra from measurements, together with improved regional models through tuning of K-profile parameterization, will lead to fundamentally improved diapycnal mixing parameterizations in ocean models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.