[A-CG47] Dynamics of Oceanic and Atmospheric Waves, Vortices, and Circulations

[ACG47-18] A formation mechanism of westward circumpolar current against westerlies in the strongly nonlinear barotropic reentrant channel

*Takuro Matsuta¹, Atsushi Kubokawa¹, Humio Mitsudera², Tomomichi Ogata³ (1.Faculty of Env.Earth Science, Hokkaido University, 2.Institute of Low Temperature Science Hokkaido University, 3.Japan Agency for Marine-Earth Science and Technology)

Keywords:Barotropic reentrant channel, Nonlinearity, Barotropic instability, Eddy momentum transport

Recent studies have indicated that even in stratified reentrant channel models, barotropic dynamics play a role in the adjustment of form stress. However, research addressing nonlinear barotropic dynamics has primarily focused on cases without external forcing or with very low seafloor topography. The impact of nonlinearities on barotropic dynamics in the presence of wind forcing and sufficiently large seamounts has not been sufficiently explored. In this study, we conduct numerical experiments using a barotropic reentrant channel forced by westerly winds to investigate the relationship between nonlinearity and circumpolar transport. In the weakly nonlinear regime, the circumpolar transport is eastward, with only a slight modification due to inertial effects. In contrast, in the strongly nonlinear regime, the circumpolar transport is westward, opposing the westerlies. We demonstrate that eddy radiation resulting from barotropic instability accelerates the mean flow westward during the initial stage of spin-up, forming a westward circumpolar current. Once the westward circumpolar current is established, it is sustained by the inertial effect of western boundary currents.