Effect of surface boundary conditions on heat transport and geostrophic balance in simulations of baroclinic waves in confined domains

In the atmosphere, baroclinic eddies are the major agents of poleward heat transport. Climate variations can impact the meridional and vertical temperature gradient and thus the baroclinic eddy heat transfer. Here, we numerically investigate the impact of a changing upper boundary condition on baroclinic instability in an analog of the planetary circulation. The setup considers the differentially heated rotating annulus experiment with either a rigid upper lid in thermal insulation or a free surface with the option of a surface heat transfer. In contrast to earlier studies, we focus on effects on the radial heat transport and the static stability of the flow, i.e., some of the most relevant issues of the planetary circulation. We find that the largest differences arise from comparing the rigid lid simulations with a free surface without heating or cooling. Additional surface heating and cooling have a minor effect on the flow. Beyond implications for geophysical fluids, the simulations help better understand earlier experiments with an upper lid and more recent experiments with a free upper surface.