The Origins of the Internal Wave Continuum: Wavenumber -frequency spectral diagnostics of forcing and energy transfer from new profiling platforms

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Intellectual Merit: Internal waves propagate long distances to provide energy for mixing in remote locations. Intermittent breaking of internal waves generate a ubiquitous background energy throughout the global oceans. This background energy is believed to sustain the meridional ocean circulation. This global circulation transports warm surface waters from the equator to the poles, in exchange for cold, deep water. This exchange maintains the climate as we know it. A coordinated examination of approximately 20 recent moored profiler (MP) and moored acoustic Doppler current profiler (ADCP) deployments in a variety of forcing environments will evaluate the parameter dependencies of the wavenumber?frequency spectra of velocity, shear, and strain and the relationships between these internal wave spectra and mixing, as diagnosed from density overturns. In particular, the observed co-variability among the broadband continuum, the near-inertial peak, internal tidal peaks, and mixing/dissipation levels will be quantified to look for spring?neap modulation of the continuum level or near-inertial peak, an elevated continuum level during times of increased wind forcing, and variation in the performance of shear- and strain-based mixing parameterizations under different spectral shapes (beyond the typically-used metric of shear?strain ratio). While an initial description of each of the MP and ADCP records has been made and salient features in both frequency and wavenumber spectra described, a valuable opportunity exists for gaining additional insight by considering this complete collection of exciting new datasets in a single study.Broader Impacts: This research project will have important implications for the development of model parameterizations, such as being pursued by the Climate Process Team (CPT) on Internal Waves and Mixing. By clarifying the impact of different types of narrowband internal waves on the continuum spectral level and mixing rates, the investigators hope to narrow the field of viable processes that need to be considered, facilitating the development of effective mixing schemes for non-wave-resolving numerical models. In addition, part of the motivation for a detailed examination of the wavenumber?frequency spectrum using highly-resolved measurements in depth and time is to aid the interpretation of coarser datasets, such as those using half-inertial pairs or a burst-sampling mode. Such measurements, with profiling floats, ship-lowered instrumentation, and moorings, have the greatest potential to provide economical global coverage of internal wave and mixing information. This project will form the basis for Brian Chinn's graduate Ph.D. dissertation, contributing to the training of a talented new member of the ocean science workforce. Both principal investigators are active in graduate student advising through their affiliation with the University of Washington's School of Oceanography. Educational outreach will be conducted through a cooperative effort between the University of Washington and the Seattle Aquarium, which hosts regular community science events (COSEE-CL), with an emphasis on bringing basic information on internal waves and the importance of ocean mixing to a public forum.