Simulations of buoyant flows driven by variations in solar radiation beneath ice cover

Spatial variations in ice and snow characteristics imply that radiative forcing in late winter lakes is spatially heterogeneous. We present idealized, three-dimensional simulations of buoyancy-driven flows, driven in this setting with heterogeneous solar radiation intensity, comparing rectilinear and radial cases. In both cases, radiative forcing in fresh water at temperatures below 4 degrees C initiates an unstable stratification near the surface, leading to Rayleigh-Taylor instabilities. The variations in radiative forcing intensity generates gravity current-like flow along the surface. The resulting flow interacts with developing three-dimensional Rayleigh-Taylor instabilities. We provide an in-depth analysis of the development and death of the gravity current-like flow in the two cases mentioned. We find that while the interaction of this current with radiatively driven convection does create instabilities along the leading edge and slow its propagation, it is mixing with the convective and warm return flow that leads to the cessation of propagation and eventual death of the current. Differences in geometry affect the depth of the shear layer between the current and return flow, determining the timing of when propagation ends.