2007/05/31 by A. J. Steffl, P. A. Delamere, F. Bagenal
Physics and Astronomy · #Astro and Planetary Science #Astronomy #Astrophysics #Azimuth #Geometry #Ionosphere and magnetosphere dynamics #Jupiter (rocket family) #Latitude #Longitude #Physics #Plasma #Solar and Space Plasma Dynamics #Torus #Variation (astronomy) #astro-ph
paper · pdf · doi:10.1016/j.icarus.2007.09.019
published as Icarus 194:153-165,2008 · Revised 24 August 2007 Accepted by Icarus, 50 pages, 2 Tables, 8 figures
arxiv created 2007/09/19 · openalex publication_date 2007/10/29 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
In this fourth paper in a series, we present a model of the remarkable temporal and azimuthal variability of the Io plasma torus observed during the Cassini encounter with Jupiter. Over a period of three months, the Cassini Ultraviolet Imaging Spectrograph (UVIS) observed a dramatic variation in the average torus composition. Superimposed on this long-term variation, is a 10.07-hour periodicity caused by an azimuthal variation in plasma composition subcorotating relative to System III longitude. Quite surprisingly, the amplitude of the azimuthal variation appears to be modulated at the beat frequency between the System III period and the observed 10.07-hour period. Previously, we have successfully modeled the months-long compositional change by supposing a factor of three increase in the amount of material supplied to Io's extended neutral clouds. Here, we extend our torus chemistry model to include an azimuthal dimension. We postulate the existence of two azimuthal variations in the number of super-thermal electrons in the torus: a primary variation that subcorotates with a period of 10.07 hours and a secondary variation that remains fixed in System III longitude. Using these two hot electron variations, our model can reproduce the observed temporal and azimuthal variations observed by Cassini UVIS.