Physics & Astronomy Colloquium (In-Person): Dr. Jody Klymak, University of Victoria

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Elliott (ELL) 168. “ Parameterizing “anti-friction” driven flow in the Antarctic Circumpolar Current ” The Antarctic Circumpolar Current is one of the strongest ocean currents, and of key importance to understanding and predicting the ocean and its response to climate change. The circulation is a delicate balance of wind forcing, eddies, and drag. Recent work has shown that more drag in the system means the current increases, a counterintuitive phenomenon known as “anti-friction.” The mechanism is that eddies, not friction, set the shear between the surface and deep currents by transferring momentum downward; friction acts on the deep flow and thereby drains energy from the eddies. More friction means weaker eddies, weaker eddies transfer less momentum out of the surface current, and so the surface circulation speeds up. After reviewing this phenomenology, we will discuss our group’s efforts to parameterize this drag that controls the eddies. The dominant source of drag is evanescent internal waves, but highly non-linear internal waves generated by stratified flow over rough topography. Using a simple parameterization of this form drag, we show that smooth seafloor can be made to have similar currents as the rough seafloor in our simulations. Globally this form drag is at least as important, and potentially more important, than other internal-wave drag sinks of eddy energy.