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Survey of thermal plasma ions in Saturn's magnetosphere utilizing a forward model
Author(s) -
Wilson R. J.,
Bagenal F.,
Persoon A. M.
Publication year - 2017
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2017ja024117
Subject(s) - magnetosphere , magnetosphere of saturn , saturn , physics , plasma , magnetopause , ion , plasma sheet , radius , proton , computational physics , atomic physics , geophysics , astrophysics , nuclear physics , planet , quantum mechanics , computer security , computer science
Abstract The Cassini Plasma Spectrometer instrument gathered thermal ion data at Saturn from 2004 to 2012, predominantly observing water group ions and protons. Plasma parameters, with uncertainties, for those two ion species are derived using a forward model of anisotropic convected Maxwellians moving at a shared velocity. The resulting data set is filtered by various selection criteria to produce a survey of plasma parameters derived within 10° of the equator at radial distances of 5.5 to 30 R S (1 R S = Saturn's radius). The previous 2008 work used a simpler method and had just 150 records over 5 orbits; this comprehensive survey has 9736 records over all 9 years. We present the results of this survey and compare them with a previous survey derived from numerical moments, highlighting the differences between the reported densities and temperatures from the two methods. Radial profiles of the plasma parameters in the inner and middle magnetospheres out to ≈22 R S are stable year by year, but variable at distances larger than 23 R S near the magnetopause. New results include proton densities increasing in the near magnetopause region, suggestive of plasma mixing; evidence for the global electric field in Saturn's inner magnetosphere extends out to ≈15 R S ; no evidence for supercorotating plasma nor the middle magnetosphere “plasma cam” feature is present; the thermal plasma β is found to exceed unity at equatorial distances greater than 15 R S .