Field Line Resonances in Jupiter's Magnetosphere

• Published in: Geophysical research letters Vol. 47; no. 18
• Main Authors: Lysak, R. L., Song, Y.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28-09-2020
• Subjects: Alfven waves; Auroral emissions; Auroral oval; Auroras; Computer simulation; Connecting; Extremely low frequencies; field line resonances; Harmonics; Jupiter; Jupiter probes; Jupiter satellites; Magnetic field; Magnetic fields; magnetic modeling; Magnetism; Magnetohydrodynamics; Mathematical models; Musical instruments; Numerical models; Orbital resonances (celestial mechanics); Oscillations; Planetary magnetic fields; Planetary magnetospheres; quasi‐periodic oscillations; Strings; Wave propagation
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2020GL089473

The arrival of the Juno satellite at Jupiter has led to an increased interest in the dynamics of the Jovian magnetosphere. Jupiter's auroral emissions often exhibit quasiperiodic oscillations with periods of tens of minutes. Magnetic observations indicate that ultralow‐frequency (ULF) waves with similar periods are often seen in data from Galileo and other satellites traversing the Jovian magnetosphere. Such waves can be associated with field line resonances, which are standing shear Alfvén waves on the field lines. Using model magnetic fields and plasma distributions, the frequencies of field line resonances and their harmonics on field lines connecting to the main auroral oval have been determined. Time domain simulations of Alfvén wave propagation have illustrated the evolution of such resonances. These studies indicate that harmonics of the field line resonances are common in the 10–40 min band.
Plain Language Summary
The magnetic field lines of planets like Earth and Jupiter can act like the strings of a musical instrument and can support waves at specific frequencies in the same way that a guitar or violin string has a particular frequency. The rapid rotation of Jupiter causes its field line to be stretched out, and Jupiter's moon Io produces a dense cloud of ionized gas (plasma) that populates these stretched field lines. By making a numerical model of Jupiter's magnetic field and plasma, we have calculated the frequencies of these field lines, which have much lower frequencies than a musical instrument so that the periods are tens of minutes. This period corresponds to oscillations in the visible aurora (northern and southern lights) at Jupiter.
Key Points
Alfvén wavefield line resonances are described in a model of Jupiter's magnetosphere based on empirical distributions of the magnetic field and plasma density
These resonances occur with periods of 10–40 min
These waves are consistent with measurements of magnetic fluctuations in Jupiter's magnetosphere, as well as with oscillations in auroral luminosity