The impact of topography and rotation in shaping the basin-scale circulation in Lough Corrib, Ireland, under homogenous conditions

Abstract

Abstract: The impact of the Earth's rotation on circulation patterns in homogenous basins has been well studied using numerical models. This contribution addresses the need for supporting observational studies. Bottom mounted acoustic doppler current (ADCP) velocity profiles are analysed alongside drifter tracks and numerical solutions in order to demonstrate how rotation modifies circulation patterns and horizontal velocity profiles in Lough Corrib, Ireland. The wind driven circulation in Lough Corrib forms a system of topographic gyres, shaped by the complex bathymetry of the basin. Surface and benthic frictional boundary layers are demonstrated to be closely described by classical Ekman theory, despite the system being constrained by shallow water depths (mean depth = 8.4m) and small horizontal dimensions (∼10km). Observed velocity profiles can be derived theoretically by summing the two driving forces of the flow (the barotropic pressure gradient force and the surface wind stress force) and their opposing forces (internal friction and Coriolis acceleration). Rotation introduces a significant cross-wind component to the flow, which is thus described as being quasi-geostrophic. The barotropic pressure gradient force is empirically quantified as a function of wind stress by relating surface set-up to the surface water shear velocity. The vertical eddy viscosity profile, derived from ADCP data, increases approximately linearly with increasing depth and is largest at the upper interface of the benthic boundary layer.