Tidal power and banding in Jupiter

Abstract

With the arrival of the Juno spacecraft at Jupiter, assumptions regarding the tidal response of Jupiter's atmosphere need to be carefully reconsidered. This is motivated both by surprising new observations as well as the fact that Juno studies have so far been conducted largely in the absence of a tidal model or assumptions that are consistent with classical tidal theory. Estimation of fully consistent tidal response solutions is somewhat tedious and for many planetary applications simplifying assumptions regarding reduced dynamics or a quasi-static balance are justified. But Jupiter's atmosphere should not be expected to be one of these simple cases because its equatorial rotation speed of ∼12 km/s near the surface exceeds most plausible internal wave speeds (including acoustic) and predicts a dynamic tidal response out of equilibrium. The goal of this study is narrowly focused on the fundamental question—does Jupiter's atmosphere contain resonantly forced tidal states? The tidal response controls the efficiency at which spin/orbit energy is deposited in the interior. The associated power levels can be enhanced by many orders of magnitude in resonantly forced states. Here classical tidal theory and Juno observations are combined and an effort is made to separate robust conclusions from ones that depend sensitively on internal-parameter assumptions. It is shown that one should expect that there are resonantly forced tides in Jupiter, and that these amplified tides may explain the observed net energy emitted from Jupiter, astrometric observations of Io's orbit implicating high tidal dissipation, and the observed banding with a dynamical boundary near ±50 degrees latitude.