Postdoctoral Fellowship: OCE-PRF: A Parameterization of Tidal and Equatorial Internal Wave Turbulence

Underwater mixing plays a critical role in regulating Earth’s climate by distributing heat, nutrients, and dissolved gases throughout the ocean. This mixing is largely driven by the breaking of internal waves, which are generated by wind and tides. However, many ocean models cannot resolve the wave breaking that drives mixing and must instead rely on simplified representations called parameterizations. One such model is the Generalized Finescale Parameterization (GFP), which infers mixing rates from measurements of the internal wave field. While effective, and an improvement on past parameterizations, the current GFP has two major limitations: it neglects energy sources beyond wind forcing and omits the equatorial ocean, where wave dynamics differ substantially. This project aims to improve the GFP by incorporating additional energy sources, such as tidal flows, and by incorporating unique wave dynamics at equatorial latitudes. These enhancements will provide a more complete understanding of the drivers of ocean mixing, reduce key uncertainties in climate models, and offer new insight into the energetic pathways that lead to mixing. The project also supports education and training through undergraduate mentorship and participation in an international oceanographic summer school.

To construct an improved parameterization, the project will analyze historical mooring and Argo float datasets to identify a minimal set of spectral parameters that capture spatiotemporal scales of non-inertial energy input. These datasets will also produce regional maps of spectral variability, with a focus on identifying biases at equatorial latitudes. The revised framework will help clarify which types of wave interactions drive mixing, an active area of debate, and how these interactions are connected to the observed wave spectrum. Once developed, the improved GFP will be applied to a real-world test case that integrates both limitations simultaneously: the Tropical Instability Wave (TIW) system of the equatorial Pacific. TIWs, a key component of the El Niño–Southern Oscillation (ENSO), are hypothesized to generate internal lee waves that may trigger a cascade toward mixing. Mooring data from the upcoming MOTIVE (Mixing belOw Tropical Instability waVEs) observations will provide mixing measurements that will be compared against GFP predictions. This will validate the improved GFP and offer new insight into connections between surface phenomena like ENSO and interior mixing. By incorporating the full suite of relevant dynamics into a refined framework, this research will yield more accurate estimates of mixing and improve the fidelity of climate simulations, informing future adaptation strategies.

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.

Award Number: 2513614
Principal Investigator: Zachary Taebel
Funds Obligated: $303,179
State: CA