Mapping Non-Local Turbulent Breakdown of Oceanic Lee Waves Offshore Costa Rica Through Seismic Oceanography

Abstract

Data analysis techniques in Seismic Oceanography are rapidly becoming more complex. Beyond first-order observation of oceanic structures it is possible to extract quantifiable information about internal wave energies and turbulent dissipation rates. We use two co-located seismic surveys taken one day apart to estimate turbulent diffusivities of lee wave breakdown with emphasis on the mid-water turbulence generated. Through a horizontal wavenumber spectral analysis of our seismic images we estimate turbulent dissipation rates throughout the cross-section. By integrating horizontal seismic slope spectra in the wavenumber domain over the turbulent subrange we obtain relative turbulent energies across the survey. To resolve absolute turbulent diffusivities we scale the relative measures to known absolute energies from tracked seismic reflectors (isopycnals). The analysis section spans 22km laterally and full ocean depth with a resolution on turbulent diffusivity of 10m vertically by 400m laterally. We focus on the region of elevated turbulent diffusivity caused by the breakdown of the lee wave above its generating site. We find the turbulent diffusivities related to the lee wave breakdown to be about 5 times greater than surrounding waters and 15 times greater than average open ocean diffusivities. We also see increased turbulent diffusivity around the rough bathymetry.