Discovery of Alfvén Waves Planetward of Saturn's Rings. Issue 2 (10th February 2021)

• Record Type: Journal Article
• Authors: Southwood, D. J.; Cao, H.; Shebanits, O.; Elsden, T.; Hunt, G. J.; Dougherty, M. K.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 2(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-02-10
• Subjects: Alfven waves -- D‐ring -- Saturn magnetosphere; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2020JA028473
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Between April and September 2017 in the final stages of the Cassini Saturn Orbiter mission the spacecraft executed 22 orbits passing planetward of the innermost ring, the D‐ring. During all periapsis passes oscillations were detected in the azimuthal magnetic field components on typical time scales of a few minutes. We argue that these time‐varying magnetic signals detected on the spacecraft are also primarily time‐varying in the plasma frame. Furthermore, we show that nearly all signals exhibit a spatial feature, namely a magnetic node near the effective field line equator. We propose that the oscillations are associated with Alfvén waves excited in local field line resonances, most likely driven from global sources. Plain Language Summary: At the end of the Cassini Saturn Orbiter space mission, the spacecraft made multiple passes on the magnetic shells that pass planetward of the rings of Saturn. On each pass, Cassini recorded oscillations in the magnetic field, Alfvén waves. However, the waves appear to be likely to be driven at the natural frequencies of the whole magnetosphere. It is as if sound from a massive wind instrument is playing a celestial violin, namely the magnetic field lines in the small cavity below the rings. Key Points: Magnetic oscillations detected near periapsis on the 22 Cassini proximal orbits are shown to be standing Alfvén waves The 3–5 nT amplitude waves, polarized in the azimuthal direction, occur on magnetic shells planetward of the Saturn D‐ring The signals are local field line resonances probably driven by coupling to global magnetospheric eigenmodes