Mesoscale eddies, internal waves, and solitons in SWOT, global models, and downscaled regional models

Principle Investigator: Brian Arbic (University of Michigan)

Co-Investigator(s): Maarten Buijsman, Eric Chassignet, Dimitris Menemenlis, Jay Shriver, Takaya Uchida, Xiaobiao Xu, Edward Zaron

Collaborator(s): Yadidya Badarvada, Loren Carrere, Marie Isabelle Pujol

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We will use high-resolution global ocean simulations (including simulations run by the US Navy and NASA) and ultra-high resolution regional ocean simulations to address several scientific questions related to the SWOT data. In previous work, we used models to anticipate what SWOT might observe. Now that SWOT data is being collected, we can enable a two-way comparison between models and observations. Models will help interpret the observations and comparisons with observations will help improve the models.

We will focus on three topics:

1. Comparison of high-resolution, two-dimensional SWOT sea surface height (SSH) data and quantities derived from SSH, such as vorticity, with a suite of high-resolution numerical ocean simulations. Comparisons of the vorticity fields in different models and in SWOT, the first altimeter to observe scales on the order of 10 km, will help to determine which, if any, of the models are realistic. Importantly, these comparisons will suggest ways to improve or adjust model representations of small-scale processes that are not resolved in global numerical simulations. We will also study nonlinear kinetic energy fluxes across different length scales, a fundamental depiction of the ocean energy budget.
2. Comparison of solitons (bundles of nonlinear internal waves) in SWOT data with results from regional ocean simulations. The unprecedented two-dimensional, high-resolution SWOT observations will test soliton models as never before. To interpret SWOT observations of solitons, we will use regional models run at the finest possible grid spacings. The models will be able to interpret dynamics that SWOT cannot measure, such as the energetics of solitons, their underwater signature, their high-frequency behavior, etc.
3. Maps of internal tides (the tidal frequency motions occurring along the interfaces between different layers in a stratified fluid) and corrections based upon the US Navy ocean forecast model. Internal tide corrections derived from ocean forecast models such as HYCOM will complement results from empirical models, the latter of which are currently at the forefront of internal tide prediction. The frequent temporal sampling of forecast models permits tidal analysis over shorter durations. The shorter analysis windows fully exploit the ability of forecast models to accurately model oceanic mesoscale eddies, which modulate internal tides on short time scales that empirical models cannot access due to infrequent temporal sampling in altimeter data. Assimilation in ocean forecast models also dramatically improves modeled sub-surface stratification, a key factor in the generation of internal tides in ocean models.

This project aims to maintain a strong US global modeling presence on the SWOT Science Team. We are collecting the main global modelers from the previous US SWOT Science Team competitions under the same umbrella. The proposed work has many benefits for the SWOT mission, NASA science and applications objectives, US Navy operations, and the US oceanographic community.