Thermodynamics of a dry atmosphere at different surface exchange rates and rotation speeds

We study the combined effect of the rotation speed Ω and of the surface ex- change rate - quantified by a surface turbulent relaxation timescale τ - on the dissipative properties of an Earth-like dry atmosphere. The rotation speed Ω is varied between one tenth and eight times that of the Earth Ω ≈ 7.29 x 10-5 rad-1 and τ from 45 minutes to 500 days. We study the circulation regimes induce by such parametric variations through two key dimensionless parame- ters, the thermal Rossby number Ro and the frictional dimensionless number Ff. An extensive analysis is performed by using nonequilibrium thermo- dynamics diagnostic tools such as material entropy production, efficiency, meridional heat transport and kinetic energy dissipation. The thermal dis- sipation associated with the sensible heat flux is found to depend mainly on the surface properties and to be almost independent from the rotation rate whereas the dissipation of kinetic energy depends in a non trivial way on both. Slowly rotating, axisymmetric circulations (Ro > 1) have the highest mechanical dissipation when the surface drag is strong (Ff ≈ 10-3) but the highest efficiency for Ff ≈ 10. For 0.01 < Ro < 1 the peak is reached for Ff ≈ 103 (τ ∼ 3 d), corresponding to the maximum activity of the baroclinic eddies, the maximum meridional heat transport and the highest efficiency. At high rotation rates (Ro < 10-2) there is a dramatic drop in the intensity of the atmospheric energy cycle and in the meridional heat transport as the at- mosphere tends towards the radiative-convective equilibrium profile. When τ is interpreted as an internal parameter, our results also confirm the vagueness of the Maximum Entropy Production Principle, since its applicability seems to be dependent on both the dissipative functions and the dynamical regime. This study suggests the effectiveness of using fundamental nonequilibrium thermodynamics to investigate the properties of planetary atmospheres.