Convection Near the Temperature-Induced Density Maximum in Water

Session: 47. - Physical Processes in Lakes

Marek Stastna, University of Waterloo, [email protected]

Abstract

It is well known that the density of freshwater achieves a maximum near four degrees Celcius. In the springtime, many natural freshwater bodies are strongly influenced by the non-monotonicity of the density-temperature curve, including the well known thermal bar phenomenon. This study presents direct numerical simulations of the onset, evolution, and decay of convective motions induced by radiatively heating a fluid that is initially at a temperature below that of the density maximum. It is demonstrated that early time dynamics take the form of a low Atwood number Rayleigh-Taylor type instability.  Motions take the form of plumes, however due to the extremely small density differences the instability induced horizontal currents are substantial, leading to prominent banding in the distribution of kinetic energy.  We compare the manner in which convection develops in deep and shallow water, maintaining the same grid pacing in the numerical simulation.  We find that for deep water the bands in the kinetic energy field penetrate far deeper into the fluid than the total depth of the shallow case.  This implies that horizontal motions in winter time lakes can be induced by radiatively forced convection.

1. Keyword
hydrodynamics

2. Keyword
mathematical models

3. Keyword
ice

4. Additional Keyword
stratified flow