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Comparative radiation belt studies by Juno and Cassini

Comparative radiation belt studies by Juno and Cassini. E. Roussos 1 , R. Thorne 2. 1: Max Planck Institute for Solar System Research, Göttingen, Germany 2: Department of Atmospheric and Oceanic Sciences, UCLA, Los Angeles, USA. Introduction. Saturn. Jupiter. L<7-10 e - : few tens of MeV

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Comparative radiation belt studies by Juno and Cassini

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  1. Comparative radiation belt studies by Juno and Cassini E. Roussos1, R. Thorne2 1: Max Planck Institute for Solar System Research, Göttingen, Germany 2: Department of Atmospheric and Oceanic Sciences, UCLA, Los Angeles, USA

  2. Introduction Saturn Jupiter L<7-10 e-: few tens of MeV ions: hundreds of MeV <107 cm-2s-1 (e- > 1MeV) H+, He++, W+, Fen+ etc. Main rings, Moons, Enceladus torus, diffuse rings, wave-particle scattering Cassini (including ENA imaging), Voyager, Pioneer, aurora imaging L<15-20 e-: up to 50-100 MeV ions: ~GeV ~108 cm-2s-1 (e- > 1MeV) H+, He++, O?+, S?+etc. Moons, Io/Europa torus, diffuse rings, wave-particle scattering Galileo, Ulysses (high. latitude), Pioneer, Voyager, Synchrotron & aurora emissions (Quasi)-dipolar region: Energies/Fluxes: Ion Composition: Loss regions: Major Datasets:

  3. Cassini radiation belt crossings Current coverage Roussos et al. (2014) Proximal/F-ring orbits

  4. Juno Radiation Belt crossings Bagenal et al. (2014)

  5. Types of measurements In situ • CAPS/JADE (Cold plasma/energetic particles) • MIMI/JEDI (Energetic particles) • RPWS/Waves (Radio & Plasma waves) • MAG/MAG (Magnetic field) Remote • UVIS/UVS/Hubble,Hisaki (UV aurora) • MIMI-INCA (Energetic neutral atoms) • RPWS/Waves (Radio/Plasma waves) • MWR/LOFAR (Synchrotron emission)

  6. Inner radiation belts (1) Flux mapping • Saturn: • Limited coverage inside L=2.8 & high latitudes • Limited pitch angle coverage Roussos et al. (2014) • Jupiter: • Limited high latitude coverage • Limited local time coverage • Contaminated/saturated measurements • Access mostly through synchrotron maps Bagenal et al. (2014)

  7. Inner radiation belts (2) Flux mapping results • Transport coefficients: • DLL ~ L3 (Jupiter – e.g. Tsuchiya et al., 2011) (thermospheric winds) • DLL ~ Ln, n>6 (Saturn) (magnetic/electric fluctuations) • Plasma/energetic particle convection • Noon/midnight electric field (Sat.) (Andriopoulou et al. 2012) • Dawn-dusk electric field (Jup.) (Barbosa & Kivelson, 1983) • Properties? (intensity, radial profile) Roussos et al. (2007) Wilson et al. (2012)

  8. Inner radiation belts (3) Flux mapping results • CRAND process • Observed at Saturn (Kollmann et al. 2013) • Ambiguous at Jupiter (Fisher et al. 1996) • Source of CRAND? • Rings or atmosphere at Saturn? • Only atmosphere at Jupiter • Are hydrogenous atmospheres effective for CRAND? • Other local sources • Electron CRAND • Energy diffusion (lightning generated whistlers) • Efficiency of multiple charge exchange Kotova et al. (this MOP) Krimigis et al. (2005)

  9. Inner radiation belts (5) Long/short term variations • Monitoring when in SW (remote observations) • Impact on middle magnetosphere (MIMI/INCA) • Impact on inner belts (LOFAR, Juno/MWR) • Response to UV input • Transients/ other periodicities or time scales • In-situ monitoring • Short period orbits, sufficient for SW time scales Roussos et al. (2014) Tsuchiya et al. (2011)

  10. Inner radiation belts (6) Transient phenomena • Transient radiation belts • Linked with CMEs at Saturn (protons) (McDonald et al. 1980; Roussos et al. 2008) • Unclear picture for electrons (Jupiter and Saturn) (Russell et al. 2001) • Combination of in-situ & remote observations will be helpful • Time scales of transient belt evolution: days to months Garrett et al. (2012) Kimura et al. (2015)

  11. Seed population (middle/outer magnetosphere) Energetic particle injections • Injections/Flux tube interchange (remote observations) • Frequency of occurrence • Spatial organization • Radial velocities • Impact on inner belts (LOFAR, Juno/MWR) • Injections/Flux tube interchange (in-situ) (e.g.Mauk et al. 1999) • Pitch angle distributions • Radial velocities • ENA imaging Dumont et al. (2014); Radioti et al. (2012)

  12. Seed population (middle/outer magnetosphere) Wave particle energization • Electrons and whistler mode chorus waves • Important for initial acceleration of seed electron population • Significant for Jupiter, role unclear for Saturn • Latitudinal distribution of chorus waves is a determining factor • Plasma frequency from electron density model is important) • Association to injections (Bolton et al. 1997) Shprits et al. (2012)

  13. Seed population (middle/outer magnetosphere) Quasi-periodic electron bursts • Impulsive electron/ion acceleration source • Electrons/ions up to few MeV • Possibly originating at high latitudes, links to aurora (Badman et al. 2012; Mitchell et al. 2015) • PAD easier to obtain with Juno • Possibly mapping to closed field lines (Roussos et al. 2015) • Signature in several instruments (Mitchell et al. 2009; McDowall et al. 1993) Palmaerts et al. (this MOP); Simpson et al. (1992)

  14. Summary • Juno/Cassini observations excellent opportunity for radiation belt studies • Combination of remote/in-situ measurements unique • Measurements by Cassini/Juno complementary – many common elements in the two systems • Earth-based observations (e.g. LOFAR) will also be important • Radiation belts are not closed systems – studying also the seed population region is essential

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