Mesoscale Ocean Eddy-Wind Interaction

Wilder, Thomas (2022) Mesoscale Ocean Eddy-Wind Interaction. Doctoral thesis, University of East Anglia.

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A surface wind stress that includes the ocean surface current (known as relative wind stress) can result in a damping of eddy energy. A weakened eddy field has significant implications for the regional and global ocean circulation. Eddy energy budget-based parameterisations currently employ an arbitrary dissipation rate, leaving some uncertainty in future climate projections. Furthermore, the role of relative wind stress on eddy dynamics is not yet fully understood.

Using shallow water theory and analytical equations, a method is developed to predict the decay of barotropic and baroclinic eddy energy due to relative wind stress. The prediction is then compared against high-resolution numerical simulations. Predicting barotropic eddy energy works well when the Rossby number is less than 0.1. Predicting baroclinic eddy energy compares well with its respective numerical simulation, although performs poorly when the numerical eddy destabilises. Eddy energy dissipation rates are then inferred via the analytical framework.

The response of an anticyclonic baroclinic eddy to relative wind stress is subsequently examined in a dedicated case study. The damping of mean kinetic energy by relative wind stress is counteracted by an additional conversion of mean potential to mean kinetic energy via linear Ekman pumping. A scaling argument between additional conversion and damping confirms these results. Linear Ekman pumping also transfers horizontal density gradients into vertical, modifying surface potential vorticity gradients. As a result, the eddy destabilises and generates instabilities earlier.
Sensitivity experiments reveal that a cyclonic eddy responds similarly to the anticyclonic case, though an earlier destabilisation takes place. An anticyclonic eddy with a more stable stratification exhibits reduced additional conversion of mean potential to mean kinetic energy due to relative wind stress.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: James Tweddle
Date Deposited: 27 Jun 2023 12:52
Last Modified: 27 Jun 2023 12:52

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