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Woodfield EE, Glauert SA, Menietti JD, Horne RB, Kavanagh AJ, Shprits YY. Acceleration of Electrons by Whistler-Mode Hiss Waves at Saturn. GEOPHYSICAL RESEARCH LETTERS 2022; 49:e2021GL096213. [PMID: 35864852 PMCID: PMC9286411 DOI: 10.1029/2021gl096213] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/21/2021] [Revised: 12/01/2021] [Accepted: 12/27/2021] [Indexed: 06/15/2023]
Abstract
Plasmaspheric hiss waves at the Earth are well known for causing losses of electrons from the radiation belts through wave particle interactions. At Saturn, however, we show that the different plasma density environment leads to acceleration of the electrons rather than loss. The ratio of plasma frequency to electron gyrofrequency frequently falls below one creating conditions for hiss to accelerate electrons. The location of hiss at high latitudes (>25°) coincides very well with this region of very low density. The interaction between electrons and hiss only occurs at these higher latitudes, therefore the acceleration is limited to mid to low pitch angles leading to butterfly pitch angle distributions. The hiss is typically an order of magnitude stronger than chorus at Saturn and the resulting acceleration is rapid, approaching steady state in one day at 0.4 MeV at L = 7 and the effect is stronger with increasing L-shell.
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Woodfield EE, Horne RB, Glauert SA, Menietti JD, Shprits YY, Kurth WS. Formation of electron radiation belts at Saturn by Z-mode wave acceleration. Nat Commun 2018; 9:5062. [PMID: 30498204 PMCID: PMC6265320 DOI: 10.1038/s41467-018-07549-4] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2017] [Accepted: 11/07/2018] [Indexed: 11/16/2022] Open
Abstract
At Saturn electrons are trapped in the planet's magnetic field and accelerated to relativistic energies to form the radiation belts, but how this dramatic increase in electron energy occurs is still unknown. Until now the mechanism of radial diffusion has been assumed but we show here that in-situ acceleration through wave particle interactions, which initial studies dismissed as ineffectual at Saturn, is in fact a vital part of the energetic particle dynamics there. We present evidence from numerical simulations based on Cassini spacecraft data that a particular plasma wave, known as Z-mode, accelerates electrons to MeV energies inside 4 RS (1 RS = 60,330 km) through a Doppler shifted cyclotron resonant interaction. Our results show that the Z-mode waves observed are not oblique as previously assumed and are much better accelerators than O-mode waves, resulting in an electron energy spectrum that closely approaches observed values without any transport effects included.
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Affiliation(s)
- E E Woodfield
- British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK.
| | - R B Horne
- British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK
| | - S A Glauert
- British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK
| | - J D Menietti
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA, 52242, USA
| | - Y Y Shprits
- Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Potsdam, 14473, Germany
- Institute for Physics and Astronomy, Universität Potsdam, 14469, Potsdam, Germany
- Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA, 90095, USA
| | - W S Kurth
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA, 52242, USA
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Kollmann P, Roussos E, Paranicas C, Woodfield EE, Mauk BH, Clark G, Smith DC, Vandegriff J. Electron Acceleration to MeV Energies at Jupiter and Saturn. JOURNAL OF GEOPHYSICAL RESEARCH. SPACE PHYSICS 2018; 123:9110-9129. [PMID: 30775196 PMCID: PMC6360449 DOI: 10.1029/2018ja025665] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/09/2018] [Revised: 08/16/2018] [Accepted: 09/24/2018] [Indexed: 06/09/2023]
Abstract
The radiation belts and magnetospheres of Jupiter and Saturn show significant intensities of relativistic electrons with energies up to tens of megaelectronvolts (MeV). To date, the question on how the electrons reach such high energies is not fully answered. This is largely due to the lack of high-quality electron spectra in the MeV energy range that models could be fit to. We reprocess data throughout the Galileo orbiter mission in order to derive Jupiter's electron spectra up to tens of MeV. In the case of Saturn, the spectra from the Cassini orbiter are readily available and we provide a systematic analysis aiming to study their acceleration mechanisms. Our analysis focuses on the magnetospheres of these planets, at distances of L > 20 and L > 4 for Jupiter and Saturn, respectively, where electron intensities are not yet at radiation belt levels. We find no support that MeV electrons are dominantly accelerated by wave-particle interactions in the magnetospheres of both planets at these distances. Instead, electron acceleration is consistent with adiabatic transport. While this is a common assumption, confirmation of this fact is important since many studies on sources, losses, and transport of energetic particles rely on it. Adiabatic heating can be driven through various radial transport mechanisms, for example, injections driven by the interchange instability or radial diffusion. We cannot distinguish these processes at Saturn with our technique. For Jupiter, we suggest that the dominating acceleration process is radial diffusion because injections are never observed at MeV energies.
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Affiliation(s)
- P. Kollmann
- The Johns Hopkins University, Applied Physics LaboratoryLaurelMDUSA
| | - E. Roussos
- Max Planck Institute for Solar System ResearchGóttingenGermany
| | - C. Paranicas
- The Johns Hopkins University, Applied Physics LaboratoryLaurelMDUSA
| | | | - B. H. Mauk
- The Johns Hopkins University, Applied Physics LaboratoryLaurelMDUSA
| | - G. Clark
- The Johns Hopkins University, Applied Physics LaboratoryLaurelMDUSA
| | - D. C. Smith
- The Johns Hopkins University, Applied Physics LaboratoryLaurelMDUSA
| | - J. Vandegriff
- The Johns Hopkins University, Applied Physics LaboratoryLaurelMDUSA
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Thomsen MF, Roussos E, Andriopoulou M, Kollmann P, Arridge CS, Paranicas CP, Gurnett DA, Powell RL, Tokar RL, Young DT. Saturn's inner magnetospheric convection pattern: Further evidence. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2011ja017482] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Schippers P, André N, Gurnett DA, Lewis GR, Persoon AM, Coates AJ. Identification of electron field-aligned current systems in Saturn's magnetosphere. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2011ja017352] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Kollmann P, Roussos E, Paranicas C, Krupp N, Jackman CM, Kirsch E, Glassmeier KH. Energetic particle phase space densities at Saturn: Cassini observations and interpretations. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2010ja016221] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- P. Kollmann
- Max Planck Institute for Solar System Research; Katlenburg-Lindau Germany
- Institut für Geophysik und Extraterrestrische Physik; Technische Universität Braunschweig; Braunschweig Germany
| | - E. Roussos
- Max Planck Institute for Solar System Research; Katlenburg-Lindau Germany
| | - C. Paranicas
- Johns Hopkins University Applied Physics Laboratory; Laurel Maryland USA
| | - N. Krupp
- Max Planck Institute for Solar System Research; Katlenburg-Lindau Germany
| | - C. M. Jackman
- Department of Physics and Astronomy; University College London; London UK
| | - E. Kirsch
- Max Planck Institute for Solar System Research; Katlenburg-Lindau Germany
| | - K.-H. Glassmeier
- Max Planck Institute for Solar System Research; Katlenburg-Lindau Germany
- Institut für Geophysik und Extraterrestrische Physik; Technische Universität Braunschweig; Braunschweig Germany
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Paranicas C, Mitchell DG, Krimigis SM, Carbary JF, Brandt PC, Turner FS, Roussos E, Krupp N, Kivelson MG, Khurana KK, Cooper JF, Armstrong TP, Burton M. Asymmetries in Saturn's radiation belts. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2009ja014971] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- C. Paranicas
- Johns Hopkins University Applied Physics Laboratory; Laurel Maryland USA
| | - D. G. Mitchell
- Johns Hopkins University Applied Physics Laboratory; Laurel Maryland USA
| | - S. M. Krimigis
- Johns Hopkins University Applied Physics Laboratory; Laurel Maryland USA
| | - J. F. Carbary
- Johns Hopkins University Applied Physics Laboratory; Laurel Maryland USA
| | - P. C. Brandt
- Johns Hopkins University Applied Physics Laboratory; Laurel Maryland USA
| | - F. S. Turner
- Johns Hopkins University Applied Physics Laboratory; Laurel Maryland USA
| | - E. Roussos
- Max-Planck-Institut für Sonnensystemforschung; Katlenburg-Lindau Germany
| | - N. Krupp
- Max-Planck-Institut für Sonnensystemforschung; Katlenburg-Lindau Germany
| | | | | | | | | | - M. Burton
- JPL; California Institute of Technology; Pasadena California USA
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Carbary JF, Mitchell DG, Krupp N, Krimigis SM. L shell distribution of energetic electrons at Saturn. ACTA ACUST UNITED AC 2009. [DOI: 10.1029/2009ja014341] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- J. F. Carbary
- Applied Physics Laboratory; Johns Hopkins University; Laurel Maryland USA
| | - D. G. Mitchell
- Applied Physics Laboratory; Johns Hopkins University; Laurel Maryland USA
| | - N. Krupp
- Max Planck Institute for Solar System Research; Lindau Germany
| | - S. M. Krimigis
- Applied Physics Laboratory; Johns Hopkins University; Laurel Maryland USA
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Dialynas K, Krimigis SM, Mitchell DG, Hamilton DC, Krupp N, Brandt PC. Energetic ion spectral characteristics in the Saturnian magnetosphere using Cassini/MIMI measurements. ACTA ACUST UNITED AC 2009. [DOI: 10.1029/2008ja013761] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- K. Dialynas
- Office for Space Research and Applications; Academy of Athens; Athens Greece
- Department of Astrophysics, Astronomy and Mechanics, Faculty of Physics; National Kapodistrian University of Athens; Athens Greece
| | - S. M. Krimigis
- Office for Space Research and Applications; Academy of Athens; Athens Greece
- Johns Hopkins University Applied Physics Laboratory; Laurel Maryland USA
| | - D. G. Mitchell
- Johns Hopkins University Applied Physics Laboratory; Laurel Maryland USA
| | - D. C. Hamilton
- Department of Physics; University of Maryland; College Park Maryland USA
| | - N. Krupp
- Max-Planck-Institut für Sonnensystemforschung; Katlenburg-Lindau Germany
| | - P. C. Brandt
- Johns Hopkins University Applied Physics Laboratory; Laurel Maryland USA
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Schippers P, Blanc M, André N, Dandouras I, Lewis GR, Gilbert LK, Persoon AM, Krupp N, Gurnett DA, Coates AJ, Krimigis SM, Young DT, Dougherty MK. Multi-instrument analysis of electron populations in Saturn's magnetosphere. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2008ja013098] [Citation(s) in RCA: 297] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- P. Schippers
- Centre d'Etude Spatiale des Rayonnements; CNRS/Université Paul Sabatier; Toulouse France
| | - M. Blanc
- Centre d'Etude Spatiale des Rayonnements; CNRS/Université Paul Sabatier; Toulouse France
| | - N. André
- Research and Scientific Support Department; European Space Agency; Noordwijk Netherlands
| | - I. Dandouras
- Centre d'Etude Spatiale des Rayonnements; CNRS/Université Paul Sabatier; Toulouse France
| | - G. R. Lewis
- Mullard Space Science Laboratory; University College London; Dorking UK
| | - L. K. Gilbert
- Mullard Space Science Laboratory; University College London; Dorking UK
| | - A. M. Persoon
- Department of Physics and Astronomy; University of Iowa; Iowa City Iowa USA
| | - N. Krupp
- Max-Planck-Institut für Sonnensystemforschung; Katlenburg-Lindau Germany
| | - D. A. Gurnett
- Department of Physics and Astronomy; University of Iowa; Iowa City Iowa USA
| | - A. J. Coates
- Mullard Space Science Laboratory; University College London; Dorking UK
| | - S. M. Krimigis
- Johns Hopkins University Applied Physics Laboratory; Laurel Maryland USA
| | - D. T. Young
- Southwest Research Institute; San Antonio Texas USA
| | - M. K. Dougherty
- Department of Space and Atmospheric Physics; Imperial College London; London UK
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