Development of overturning circulation in sloping waterbodies due to surface cooling
Metadatos
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Cambridge University Press
Materia
Convection in cavities Buoyancy-driven instability Topographic effects
Fecha
2021-11-10Referencia bibliográfica
Ulloa, H... [et al.] (2022). Development of overturning circulation in sloping waterbodies due to surface cooling. Journal of Fluid Mechanics, 930, A18. doi:[10.1017/jfm.2021.883]
Patrocinador
Swiss National Science Foundation (SNSF) European Commission 175919; Physics of Aquatic Systems Laboratory (APHYS), EPFLResumen
Cooling 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–Bénard 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.