Saturn’s Weather-Driven Aurorae Modulate Oscillations in the Magnetic Field and Radio Emissions

Chowdhury, M.N. and Stallard, T.S. and Baines, K. H. and Provan, G. and Melin, Henrik and Hunt, G. J. and Moore, Luke and O'Donoghue, James and Thomas, Emma M. and Wang, Ruoyan and Miller, Steve and Badman, Sarah (2022) Saturn’s Weather-Driven Aurorae Modulate Oscillations in the Magnetic Field and Radio Emissions. Geophysical Research Letters, 49 (3): e2021GL096. ISSN 0094-8276

Text (M_N_Chowdhury_et_al_2021)
M_N_Chowdhury_et_al_2021.pdf - Accepted Version
Available under License Creative Commons Attribution.
Download (438kB)

Abstract

The Cassini spacecraft revealed that Saturn's magnetic field displayed oscillations at a period originally thought to match the planetary rotation rate but later found not to. One of many proposed theories predicts that a polar twin-cell neutral weather system drives this variation, producing observable differences in flows within Saturn's ionosphere. Here, using spectral observations of auroral urn:x-wiley:00948276:media:grl63524:grl63524-math-0001 emission lines taken by the Keck Observatory's Near Infrared Echelle Spectrograph (Keck-NIRSPEC) in 2017, we derive ion line-of-sight velocity maps after grouping spectra into rotational quadrants matching phases of the planetary magnetic field. We measure 0.5 km s−1 wind systems in the ionosphere consistent with predicted neutral twin-vortex flow patterns. These findings demonstrate that neutral winds in Saturn's polar regions cause the rotational period, as determined via the magnetic field, to exhibit differences and time variabilities relative to the planet's true period of rotation in a process never before seen within planetary atmospheres.