This TRR 181 seminar will be held by Nobuhiro Suzuki (Université de Bretagne Occidentale) on
Two-way coupling between a deep-water wave and a roll circulation
at Universität Hamburg on June 21th at 10 am, Bundesstr. 53, Room 22/23 (ground floor).
The interaction between surface gravity waves and roll circulations accompanied by along-roll jets (e.g., Langmuir circulation or submesoscale frontal circulation) affects the upper-ocean biochemical and physical processes. To improve the previous theoretical limitations with regard to the incompressibility, shear, and vertical velocities of roll circulations, a theory is developed for the two-way interaction between a deep-water wave and a roll circulation nearly parallel to the wavenumber. The theory uses a surface-following coordinate system to unequivocally define the oscillatory and non-oscillatory motions even at the heights above the wave trough and derives the higher-order wave solutions resulting from the interaction between the current and the leading-order wave without assuming irrotationality of the higher-order waves. The result shows a clear effect of the roll circulation on the tendencies of the wave amplitude and the wave action density. Using the wave solutions obtained, the equations of motion to be used by wave-averaged, nonhydrostatic, circulation models are derived. These equations are similar to a conventional set of wave-averaged equations commonly known as the Craik-Leibovich equations but critically different in two aspects concerning the incompressibility of the wave-averaged flow and a wave-refraction effect. It is also shown that a crucial force acting on the wave-averaged flow results from the interaction between the leading-order wave and some of the current-influenced, higher-order waves. This research sheds light on the energy transfer between waves and currents and is a step towards investigating more complete energy transfer involved in the wind-wave-current coupled system.