Superrotation in Planetary Atmospheres

Superrotation occurs when the atmosphere of a planet spins faster than the planet beneath it.  More precisely, it occurs when the angular momentum of a ring of air is greater than the angular momentum of the solid planet at the equator.   In the Solar System, Venus, Titan, Jupiter and Saturn all superrotate, and Earth and Mars do occasionally.  Some exoplanets, in particular tidally-locked ones, are thought to superrotate.  I will discuss the various mechanisms that give rise to superrotation, drawing similarities and differences between slow rotators (like Venus), the fast rotators (like Jupiter) and tidally-locked exoplanets.