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Two-dimensional Ekman-Inertial Instability

Submesoscale ocean flows are energetically relevant because they could provide a path for dissipation from large to small scales. In addition, they induce large vertical velocities that enhance the transport of mass, heat, gases, and nutrients. Dynamically speaking, submesoscale flows are especially prone to undergo instabilities. In particular, Ekman-Inertial Instability (EII) has recently been theoretically predicted to develop in submesoscale flows forced by a sudden change in surface wind stress. EII is characterised by non-normal growth rates and its time evolution initially follows that of the atmospheric conditions that trigger it. Consequently, EII may grow at a much faster rate than other common interior submesoscale instabilities.

In this talk, I will present a comparison between the development of Inertial Instability and EII in a 2D submesoscale current, focusing on the vertical motions induced in each case. The results show that EII develops much faster and induces a vertical flow much stronger than the one induced by Inertial Instability. Moreover, Inertial Instability and EII both grow fast enough to emit internal waves. However, their very different growth rates result in very different frequency spectra for the internal wave field. I will present two attempts to separate the internal wave field from the mean flow: an Eulerian and a Lagrangian approach. The performance, as well as the advantages and disadvantages of each method will be discussed.

Host: Ramina Alwarda
Event series  Brewer-Wilson Seminar Series