Thermobaric effect on slantwise convection in cold seawater

A theoretical investigation shows that the pressure dependence of the thermal expansion coefficient (the thermobaric effect) acts to destabilize stratified geostrophic flows when both temperature and salinity contribute positively to the vertical stability. For vertical stability where the salinity contributes negatively, the thermobaric effect may act to stabilize the flow. The considered disturbances are small-amplitude two-dimensional rolls with axes aligned along the basic geostrophic current, and the growth mechanism is symmetric baroclinic instability. The boundaries of the marginally stable convection cells are essentially parallel to the slanting isopycnals of the basic state; therefore, the term slantwise convection is used to describe this phenomenon. Furthermore, the thermobaric effect induces a shift of the centres of the convection cells towards the lower part of the fluid layer, as previously demonstrated for buoyancy-driven convection. The width of the marginally stable cells is small and determined by turbulent diffusion processes in the fluid.