Does Jupiter’s magnetosphere ring like a bell? Investigating the system response to externally driven ultra-low-frequency waves

Abstract:

The key importance of waves in the magnetosphere at Jupiter has received renewed appreciation in the wake of findings from the ongoing Juno mission. Ultra-low-frequency waves in particular may play a large role in magnetospheric dynamics on a global scale, providing energy and momentum channels and modulating myriad processes (e.g. auroral pulsations). Recent findings have shown that a large population of these waves permeates the magnetosphere, but the mechanisms that generate system-scale perturbations are still a matter of speculation.

We present a study utilizing a rare opportunity to use multi-point measurements of a Jovian-type magnetosphere. During December 2000 – January 2001 Cassini flew by the noon-dusk boundary of the magnetosphere, skimming the magnetosheath and sporadically encountering the magnetopause. During the same interval, Galileo was in-situ within the magnetosphere proper, outbound through the dusk sector.

We used magnetometer data from both spacecraft to analyse the penetration of ultra-low-frequency (system-scale wavelength) wave sources into the magnetosphere from the system boundary. Using spectral analysis techniques, we inspected the geometry of significant wave sources to distinguish between freely propagating waves in the magnetosheath and surface waves on the magnetopause.

We compared the spectral properties of waves inside and outside the system boundary, to determine possible induced resonances of the magnetic field by broadband sources. By inspecting the correlation of large-scale waves between the two datasets, we attempted to constrain the driving and response delay-time of the system, and to what extent the system responds coherently to such external influence.