Three-dimensional gravity flows in an idealized stratified ice-covered lake

The combined effect of gravity and viscosity forces produces a flow along any inclined solid lateral wall in a density-stratified fluid. The flow becomes an important driver of circulation in ice-covered lakes isolated from wind forcing. We present numerical results from the Regional Ocean Modeling System (ROMS) investigating three-dimensional buoyancy-driven circulation in an ice-covered lake of simplified symmetric shape. The numerical results revealed vertical current velocities of 10^-6 m s^-1 and horizontal current velocities of 10^-3 m s^-1. The model simulated an upward current along sloping boundaries, with downwelling return flow throughout the bulk of the lake's water column. For the typical internal Rossby radius of 14 km, basin-scale circulation in a lake with a horizontal dimension of 45 km turns to a counterclockwise gyre in the lake half depth. We investigated the dependence of the boundary flow and the residual lake-wide circulation on the lake size, bottom slope inclination, and earth rotation. The obtained magnitudes of the boundary flow were compared against known simplified analytical solutions. The outcomes demonstrated that the ROMS model, on the basis of the Boussinesq hydrostatic equation, is able to simulate weakly energetic flows governed by viscous forces and rotation in enclosed thermally stratified ice-covered domains. The results contribute to a better understanding of the processes driving the under-ice freshwater circulation with wider applications, including dynamics of buoyancy-driven flows affected by nonlinear effects, such as freshwater density anomaly.