Evolution of electron pitch angle distributions across Saturn's middle magnetospheric region from MIMI/LEMMS

G. Clark, C. Paranicas, D. Santos-Costa, S. Livi, N. Krupp, D. G. Mitchell, E. Roussos, W. L. Tseng

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

We provide a global view of ∼20 to 800 keV electron pitch angle distributions (PADs) close to Saturn's current sheet using observations from the Cassini MIMI/LEMMS instrument. Previous work indicated that the nature of pitch angle distributions in Saturn's inner to middle magnetosphere changes near the radial distance of 10RS. This work confirms the existence of a PAD transition region. Here we go further and develop a new technique to statistically quantify the spatial profile of butterfly PADs as well as present new spatial trends on the isotropic PAD. Additionally, we perform a case study analysis and show the PADs exhibit strong energy dependent features throughout this transition region. We also present a diffusion theory model based on adiabatic transport, Coulomb interactions with Saturn's neutral gas torus, and an energy dependent radial diffusion coefficient. A data-model comparison reveals that adiabatic transport is the dominant transport mechanism between ∼8 to 12RS, however interactions with Saturn's neutral gas torus become dominant inside ∼7RS and govern the flux level of ∼20 to 800 keV electrons. We have also found that field-aligned fluxes were not well reproduced by our modeling approach. We suggest that wave-particle interactions and/or a polar source of the energetic particles needs further investigation.

Original languageEnglish
Pages (from-to)18-28
Number of pages11
JournalPlanetary and Space Science
Volume104
Issue numberPA
DOIs
Publication statusPublished - 2014 Dec 1

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Keywords

  • Electron pitch angle distributions
  • Electron transport and loss mechanisms
  • Saturn Cassini
  • Transition region

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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