Flow asymmetry over varying topography: Implications for large-scale circulation

Ocean flows interacting with topography are critical for shaping large-scale circulation in polar regions such as the Arctic Ocean, where strong topographic steering shapes flow along continental slopes. Flow over sloping topography with corrugations exhibits an asymmetric response to prograde versus retrograde forcing, with stronger and more laminar flows in the prograde case (here, prograde forcing aligns with topographic wave propagation, while retrograde forcing opposes it). Previous studies attribute this asymmetry to increased topographic form stress for retrograde forcing. To further investigate these dynamics, we analyze flow responses to time-variable forcing over corrugated slopes using momentum budgets along depth-following contours. In this framework, the topographic form stress term vanishes, and vorticity fluxes across depth-contours emerge as the dominant mechanism driving asymmetries.

Preliminary results from idealized shallow water simulations reveal distinct nonlinear flow behaviors. For shorter forcing periods, the flow exhibits a cyclonic shift consistent with the "Neptune effect." For longer forcing periods, retrograde flow strength saturates, plateauing even as forcing increases. These findings build on our previous analysis of a realistic Arctic Ocean simulation, which indicated that these nonlinear effects leave an imprint on large-scale circulation. Together, they suggest that mesoscale topography-flow interactions modulate large-scale circulation and contribute to temporal variability in polar oceans under changing forcing conditions.