Internal Tide Studies at the Hawaiian Ridge

University Of Hawaii, Honolulu

Investigators

Abstract

0425347 Intellectual merit: The pathways of energy transfer from the basin-scale surface tidal motions to the smallest turbulent mixing scales are not understood well. An important intermediate step is the scattering of the surface tide into internal tides at mid-ocean topography, such as seamounts, submerged ridges, and islands, which is a sink for barotropic tidal energy. Models show internal tides emanating from these generation regions with both beam structure, where energy density is localized along internal tidal characteristics, and low-mode structure. The high-mode components of the internal tide are believed to dissipate near the generation site and may be important for local mixing, while the low-mode internal tides propagate away from their source regions with decay scales on the order of 1000 km in observations and models. Our ability to predict this process depends on well-conceived models that are validated against field observations. The largest and most comprehensive tidal conversion study has been the Hawaii Ocean Mixing Experiment (HOME), focusing on tidal scattering at the ridge, seamount, and island topography making up the Hawaiian Ridge. The modeling component of this study has proven to be highly successful. The model simulations of internal tide generation and radiation compares favorably to observed currents, displacements, energy densities, energy fluxes, and dissipation. The continuation of the HOME tidal modeling effort is based on the Princeton Ocean Model. The goals of this project are to 1) finalize the tidal energy budget for the entire ridge, 2) examine non-hydrostatic features observed over the ridge crest, 3) assess the model turbulent closure scheme versus direct microstructure and finestructure measurements, 4) determine the amount of deep mixing occurring along the ridge flanks associated with internal tide beams, and 5) assess the sensitivity of the internal tide to changes in the background stratification and circulation. HOME provides an ideal test site to expand our understanding of the tidal scattering process, to assess current modeling approaches, and to develop new tools based on the field results. Broader impacts: Ultimately this activity can lead to improved parameterizations of tidal dissipation and mixing to be used in larger scale circulation and climate models, as well as in regional models for seamount and ridge environments. An undergraduate and two graduate student will participate in this project, with the goal of achieving a senior thesis and PhD dissertations. The project will be highlighted during the annual public open house at the University of Hawaii, an outreach activity sponsored by the School of Ocean Earth Science and Technology. The Bishop Museum in Honolulu, Hawaii will be contacted to discuss a possible display based on the results of this study.