Ulloa, Hugo N.Ramon, Cintia L.Doda, TomyWuest, AlfredBouffard, Damien2021-12-042021-12-042021-12-042021-11-1010.1017/jfm.2021.883https://infoscience.epfl.ch/handle/20.500.14299/183616WOS:000721330000001Cooling the surface of freshwater bodies, whose temperatures are above the temperature of maximum density, can generate differential cooling between shallow and deep regions. When surface cooling occurs over a long enough period, the thermally induced cross-shore pressure gradient may drive an overturning circulation, a phenomenon called 'thermal siphon'. However, the conditions under which this process begins are not yet fully characterised. Here, we examine the development of thermal siphons driven by a uniform loss of heat at the air-water interface in sloping, stratified basins. For a two-dimensional framework, we derive theoretical time and velocity scales associated with the transition from Rayleigh-Benard type convection to a horizontal overturning circulation across the shallower sloping basin. This transition is characterised by a three-way horizontal momentum balance, in which the cross-shore pressure gradient balances the inertial terms before reaching a quasi-steady regime. We performed numerical and field experiments to test and show the robustness of the analytical scaling, describe the convective regimes and quantify the cross-shore transport induced by thermal siphons. Our results are relevant for understanding the nearshore fluid dynamics induced by nighttime or seasonal surface cooling in lakes and reservoirs.MechanicsPhysics, Fluids & PlasmasPhysicsconvection in cavitiesbuoyancy-driven instabilitytopographic effectsunsteady natural-convectiontemporal variabilityexchange flowswatershoreshallowlakestransportmethanesidearmtext::journal::journal article::research article