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Flushing the Lake Littoral Region: The Interaction of Differential Cooling and Mild Winds
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  • Cintia Luz Ramón Casañas,
  • Hugo N. Ulloa,
  • Tomy Doda,
  • Damien Bouffard
Cintia Luz Ramón Casañas
Water Research Institute and Department of Civil Engineering, University of Granada, Spain

Corresponding Author:[email protected]

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Hugo N. Ulloa
Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, USA
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Tomy Doda
Department of Surface Waters – Research and Management
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Damien Bouffard
Department of Surface Waters – Research and Management
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The interaction of a uniform cooling rate at the lake surface with sloping bathymetry efficiently drives cross-shore water exchanges between the shallow littoral and deep interior regions. The faster cooling rate of the shallows results in the formation of density-driven currents, known as thermal siphons, that flow downslope until they intrude horizontally at the base of the surface mixed layer. Existing parameterizations of the resulting buoyancy-driven cross-shore transport assume calm wind conditions which are, however, rarely observed in lakes and thereby strongly restrict their applicability. Here we examine how moderate winds (≲ 5 m s-1) affect this convective cross-shore transport. We derive simple analytical solutions that we further test against realistic three-dimensional numerical hydrodynamic simulations of an enclosed stratified basin subject to uniform and steady surface cooling rate and cross-shore winds. We show cross-shore winds modify the convective circulation, stopping or even reversing it in the upwind littoral region and enhancing the cross-shore exchange in the downwind region. The magnitude of the simulated offshore unit-width discharges in the upwind and downwind littoral regions was satisfactorily predicted by the analytical parameterization. Our scaling expands the previous formulation to a regime where both wind and buoyancy forces drive cross-shore discharges of similar magnitude. This range is defined by the non-dimensional Monin-Obukhov length scale, χMO: 0.1 ≲ χMO ≲0.5. The information needed to evaluate the scaling formula can be readily obtained from a traditional set of in-situ observations.