Error analysis for numerical estimates of space plasma parameters

Wilson, R.

doi:10.1002/2014ea000090

Cited by 9 publications

(7 citation statements)

References 24 publications

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“…We apply the code MPFIT (Levenberg‐Marquardt technique) to apply a nonlinear least squares minimization to find the best fit of the model to an observed spectrum. We then compute the curvature matrix at the best fit to find the associated uncertainties in the fit parameters [ Wilson , ].…”

Section: Methodsmentioning

confidence: 99%

Io plasma torus ion composition: Voyager, Galileo, and Cassini

2017

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The Io torus produces ultraviolet emissions diagnostic of plasma conditions. We revisit data sets obtained by the Voyager 1, Galileo, and Cassini missions at Jupiter. With the latest version (8.0) of the CHIANTI atomic database we analyze UV spectra to determine ion composition. We compare ion composition obtained from observations from these three missions with a theoretical model of the physical chemistry of the torus by Delamere et al. (2005). We find ion abundances from the Voyager data similar to the Cassini epoch, consistent with the dissociation and ionization of SO2, but with a slightly higher average ionization state for sulfur, consistent with the higher electron temperature measured by Voyager. This reanalysis of the Voyager data produces a much lower oxygen:sulfur ratio than earlier analysis by Shemansky (1988), which was also reported by Bagenal (1994). We derive fractional ion compositions in the center of the torus to be S+/Ne ~ 5%, S++/Ne ~ 20%, S+++/Ne ~ 5%, O+/Ne ~ 20%, O++/Ne ~ 3%, and Σ(On+)/Σ(Sn+) ~ 0.8, leaving about 10–15% of the charge as protons. The radial profile of ion composition indicates a slightly higher average ionization state, a modest loss of sulfur relative to oxygen, and Σ(On+)/Σ(Sn+) ~ 1.2 at about 8 RJ, beyond which the composition is basically frozen in. The Galileo observations of UV emissions from the torus suggest that the composition in June 1996 may have comprised a lower abundance of oxygen than usual, consistent with observations made at the same time by the EUVE satellite.

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Section: Methodsmentioning

confidence: 99%

Io plasma torus ion composition: Voyager, Galileo, and Cassini

2017

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“…Filtering on the uncertainties [Wilson, 2015] are far more useful as bad fits can have unphysically tiny (<0.1%) or ridiculously large (100s%) values.…”

Section: Forward Model Fittingmentioning

confidence: 99%

Survey of thermal plasma ions in Saturn's magnetosphere utilizing a forward model

2017

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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 RS (1 RS = 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 ≈22RS are stable year by year, but variable at distances larger than 23 RS 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 ≈15RS; 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 RS.

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“…Uncertainties in the determination of the fitted parameters are found by taking the square root of the diagonals of the covariance matrix for the reduced chi‐square fit, where the covariance matrix is the inverse of the curvature matrix [ Wilson , ]. The supporting information describes the method in full detail including prepruning the data to be fitted, limits and constraints used to aid a faster and more physical fit, and postpruning of the fitted data.…”

Section: Analysis Techniquesmentioning

confidence: 99%

Survey of Galileo plasma observations in Jupiter's plasma sheet

et al. 2016

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The plasma science (PLS) instrument on the Galileo spacecraft (orbiting Jupiter from December 1995 to September 2003) measured properties of the ions that were trapped in the magnetic field. The PLS data provide a survey of the plasma properties between ~5 and 30 Jupiter radii (RJ) in the equatorial region. We present plasma properties derived via two analysis methods: numerical moments and forward modeling. We find that the density decreases with radial distance by nearly 5 orders of magnitude from ~2 to 3000 cm−3 at 6 RJ to ~0.05 cm−3 at 30 RJ. The density profile did not show major changes from orbit to orbit, suggesting that the plasma production and transport remained constant within about a factor of 2. The radial profile of ion temperature increased with distance which implied that contrary to the concept of adiabatic cooling on expansion, the plasma heats up as it expands out from Io's orbit (where Ti ~ 60–80 eV) at ~6 RJ to a few keV at 30 RJ. There does not seem to be a long‐term, systematic variation in ion temperature with either local time or longitude. This latter finding differs from earlier analysis of Galileo PLS data from a selection of orbits. Further examination of all data from all Galileo orbits suggests that System III variations are transitory on timescales of weeks, consistent with the modeling of Cassini Ultraviolet Imaging Spectrograph observations. The plasma flow is dominated by azimuthal flow that is between 80% and 100% of corotation out to 25 RJ.

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Error analysis for numerical estimates of space plasma parameters

Cited by 9 publications

References 24 publications

Io plasma torus ion composition: Voyager, Galileo, and Cassini

Io plasma torus ion composition: Voyager, Galileo, and Cassini

Survey of thermal plasma ions in Saturn's magnetosphere utilizing a forward model

Survey of Galileo plasma observations in Jupiter's plasma sheet

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