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  Energetic Ion Moments and Polytropic Index in Saturn's Magnetosphere using Cassini/MIMI Measurements: A Simple Model Based on κ‐Distribution Functions

Dialynas, K., Roussos, E., Regoli, L., Paranicas, C. P., Krimigis, S. M., Kane, M., et al. (2018). Energetic Ion Moments and Polytropic Index in Saturn's Magnetosphere using Cassini/MIMI Measurements: A Simple Model Based on κ‐Distribution Functions. Journal of Geophysical Research: Space Physics, 123(10), 8066-8086. doi:10.1029/2018JA025820.

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 Creators:
Dialynas, Konstantinos, Author
Roussos, Elias1, Author              
Regoli, Leonardo, Author
Paranicas, Christopher P., Author
Krimigis, Stamatios M., Author
Kane, Mark, Author
Mitchell, Donald G., Author
Hamilton, Douglas C., Author
Krupp, Norbert1, Author              
Carbary, James F., Author
Affiliations:
1Department Planets and Comets, Max Planck Institute for Solar System Research, Max Planck Society, ou_1832288              

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 Abstract: Moments of the charged particle distribution function provide a compact way of studying the transport, acceleration, and interactions of plasma and energetic particles in the magnetosphere. We employ κ‐distributions to describe the energy spectra of H+ and O+, based on >20 keV measurements by the three detectors of Cassini's Magnetospheric Imaging Instrument, covering the time period from DOY 183/2004 to 016/2016, 5 < L < 20. From the analytical spectra we calculate the equatorial distributions of energetic ion moments inside Saturn's magnetosphere and then focus on the distributions of the characteristic energy (Ec=IE/In), temperature, and κ‐index of these ions. A semiempirical model is utilized to simulate the equatorial ion moments in both local time and L‐shell, allowing the derivation of the polytropic index (Γ) for both H+ and O+. Primary results are as follows: (a) The ∼9 < L < 20 region corresponds to a local equatorial acceleration region, where subadiabatic transport of H+ (Γ∼1.25) and quasi‐isothermal behavior of O+ (Γ∼0.95) dominate the ion energetics; (b) energetic ions are heavily depleted in the inner magnetospheric regions, and their behavior appears to be quasi‐isothermal (Γ<1); (c) the (quasi‐) periodic energetic ion injections in the outer parts of Saturn's magnetosphere (especially beyond 17–18 RS) produce durable signatures in the energetic ion moments; (d) the plasma sheet does not seem to have a ground thermodynamic state, but the extended neutral gas distribution at Saturn provides an effective cooling mechanism that does not allow the plasma sheet to behave adiabatically.

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Language(s): eng - English
 Dates: 2019-04-242018
 Publication Status: Published in print
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1029/2018JA025820
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Title: Journal of Geophysical Research: Space Physics
  Other : JGR-A
  Abbreviation : J. Geophys. Res. - A
Source Genre: Journal
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Publ. Info: Washington, D.C. : American Geophysical Union
Pages: - Volume / Issue: 123 (10) Sequence Number: - Start / End Page: 8066 - 8086 Identifier: ISSN: 0148-0227
CoNE: https://pure.mpg.de/cone/journals/resource/991042728714264