We calculate low-|m| inertial mode oscillations of Jupiter. Inertial modes are rotationally induced oscillations characterized by the fact that the kinetic energy dominates the potential energy of oscillation. Such modes propagate in isentropic regions of rotating bodies. Since Jupiter is believed to be in convective equilibrium and to have a nearly isentropic structure, it is expected to exhibit inertial mode oscillations. Inertial modes have low frequencies, comparable with the rotation frequency, and they usually have large horizontal and toroidal velocity components near the surface. In the present study, we have computed the properties of the inertial mode oscillations by expanding the displacement vectors associated with the oscillation in an infinite series of spherical harmonics. We have truncated the infinite system of coupled ordinary differential equations which results to two terms for most of our calculations, and we assess the accuracy of this approximation by performing a limited set of calculations using a three-term expansion. We have used several models for Jupiter, including one that incorporates the so-called "plasma phase transition" (PPT) as well as one without. The PPT is a first-order phase transition between the metallic and the molecular phases of dense hydrogen. If it actually exists, the PPT will produce a density discontinuity in the hydrogen-rich envelopes of the giant planets. We show that the inertial modes of Jupiter are affected by this density discontinuity. We also find interfacial discontinuity modes, which have large amplitudes just at the density discontinuity associated with the PPT. In addition, we discuss the general properties of inertial modes in giant planets by calculating the inertial modes of a polytropic model with polytropic index n = 1. Our calculations show that the periods of the inertial modes of Jupiter, observed in the corotating frame, range from several hours to about 100 hr, while the periods of the discontinuity modes are several hours.
- Planets and satellites: individual (Jupiter)
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science