Interactions Between Internal Tidal Bores and Submesoscale Currents on the Continental Shelf

A realistic simulation of Central California reveals interactions between shoaling internal tidal bores and submesoscale currents on the inner-shelf (approximately 30-60 m depth). These interactions comprise collisions between internal tidal upwelling, & quot;forward & quot; bores (FBs) with submesoscale currents (SMCs) in the form of surface layer density fronts or filaments with downwelling secondary circulation. Along-shore oriented FBs collide with both cross-shore (perpendicular interaction) or along-shore (parallel interaction) oriented SMCs. In perpendicular interaction, FBs colliding into cross-shore oriented SMCs refract around the offshore tip of the downwelling front or filament. SMCs generally survive perpendicular interaction, despite partial disruption of downwelling secondary circulation by FBs. An example of parallel interaction demonstrates regional wind regulating the competition between FBs and SMCs to set cross-shore stratification structure. This example comprises (a) blocking of FB propagation by elevated mixing (strong wind) and dense filament formation on the inner-shelf and (b) the subsequent destruction of the dense filament that is initiated by a decrease in vertical mixing (weakening wind) and completed by renewed FB propagation underneath it. For both perpendicular and parallel interaction, FB propagation is modulated by a varying medium introduced by SMC density and current structure. The computational evidence of these interactions corroborates recent observations of interactions between small-scale, nearshore currents in the real ocean. This study motivates further exploration of interactions between fronts, filaments, internal tidal bores, and vortices in the nearshore.