Thermally Driven Angular Momentum Transport in Hot Jupiters

We study the angular momentum transport inside hot Jupiters under the influence of gravitational and thermal forcing. Due to the strong stellar irradiation, a radiative region develops on top of the convective region. Internal gravity waves are launched at the radiative–convective boundaries (RCBs). The thermal response is dynamical and plays an important role in the angular momentum transport. By separating the gravitational and thermal forcing terms, we identify the thermal effects of increasing the angular momentum transport. For the low-frequency (in the corotating frame with planets) prograde (retrograde) tidal frequency, the angular momentum flux is positive (negative). The tidal interactions tend to drive the planet to the synchronous state. We find that the angular momentum transport associated with the internal gravity wave is very sensitive to relative position between the RCB and the penetration depth of the thermal forcing. If the RCB is in the vicinity of the thermal forcing penetration depth, even with small amplitude thermal forcing, the thermally driven angular momentum flux could be much larger than the flux induced by gravitational forcing. The thermally enhanced torque could drive the planet to the synchronous state in as short as a few 104 yr.