Different tidal torques on a planet with a dense atmosphere and consequences to the spin dynamics

Planets with a dense atmosphere present not only traditional gravitational and thermal tides, but also combined effects resulting from these two: gravitational torque upon pressure bulge, pressure torque upon tidal bulge, and pressure torque upon pressure bulge. Here we give a complete description of these effects and evaluate their relative contributions to the secular evolution of the planet's spin. In particular, we discuss the importance of determining the exact transfer mechanism of angular momentum from the atmosphere to the surface. It is shown that alternative atmospheric tides may play an important role if this transfer rate is not very effective, although this does not seem to be the present case on Earth or Venus.