South China Sea Annual Meeting 2023 (SCSAM)

96 / 2023-07-30 10:53:58

The influence of tidal currents on the shoreward transmission of open-ocean signals

Bottom friction; Tidal current; Open-ocean sea level

Our aim in this paper is to investigate how the presence of tidal current alters the relationship between open-ocean dynamics and coastal sea level. Oceanic signal transmission onto and across the continental shelf/slope to the coast is limited to the frictional-decay distance; that is, friction aids signal transmission. Assuming a linearized equation of motion, the tidal effect on the transmission of interior sea level can be described with a function of dimension parameter. The parameter \(R = f{\sqrt{2\mu \over |f\pm\omega|} }\)(i.e., bottom friction coefficient) is found to mainly determine the contribution of open-ocean signals to coastal sea level with \(f\) the Coriolis parameter, \(\omega\) the frequency of the tidal constituent concerned, and \(\mu\) the eddy viscosity. Large (small) \(R\) gives maximum penetration (insulation) of open-ocean sea level. In areas dominated by the M₂ tide, the anticyclonic (cyclonic) tidal currents would enhance (weaken) the penetration and can have a large (small) impact on coastal sea level. Estimating the averaged eddy viscosity from the moored acoustic Doppler current profiler data, the penetration at spring tide is larger than at neap tide.