Boundary flow on a lake slope during Ekman layer arrest

Abstract

The disruption of an arrested bottom Ekman layer on a lake boundary slope is initiated when buoyancy enters the balance between the Coriolis force and the pressure gradient. This process is shown to behave in a lake in a qualitatively similar manner to the ocean. A greater bottom slope and stronger stratification are found to dramatically shorten the shutdown timescale of the Ekman flux compared to typical values on the continental shelf and slope. Convergence of the flow at the density front, where the thermocline intersects the bottom, leads to a detrainment of bottom boundary layer water into the interior of the lake and thus facilitates the transport of mass and heat independent of turbulence generation in the boundary layer by internal wave interactions. Internal waves complicate the flow structure. The boundary water detrainment and gravitational instability due to Ekman layer dynamics and the critical reflection and vertical overturns associated with the internal waves combine in effective boundary mixing. Copyright 2006 by the American Geophysical Union.