Bathymetric influence on the coastal sea level response to ocean gyres at western boundaries

Abstract

It is our aim with this paper to investigate how the presence of a continental shelf and slope alters the relationship between interior ocean dynamics and western boundary (coastal) sea level. The assumption of a flat-bottomed basinwith vertical sidewall at the coast is shown to hide the role that depth plays in the net force actingon thecoast. A linear β-plane theory is then developed describing the transmission of sea level over variable depth bathymetry as analogous to the steady advection-diffusion of a thermal fluid. The parameter P a =βHL (x) /r, relating the friction parameter r to the bathymetry depth H and width L (x) , is found to determine the contribution of interior sea level to coastal sea level, with small P a giving maximum penetration and large P a maximum insulation. In the smallP a (infinite friction) limit the frictional boundary layer extends far offshore, and coastal sea level tends toward the vertical sidewall solution. Adding simple stratification produces exactly the same result but with reduced effective depth and hence enhanced penetration. Penetration can be further enhanced by permitting weakly nonlinear variations of thermocline depth.Wider and shallower shelves relative to the overall scales are also shown to maximize penetration for realistic values of P a (≤10). The theory implies that resolution of bathymetry and representation of friction can have a large impact on simulated coastal sea level, calling into question the ability of coarse-resolution models to accurately represent processes determining the dynamic coastal sea level.