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Staples FA, Kellerman A, Murphy KR, Rae IJ, Sandhu JK, Forsyth C. Resolving Magnetopause Shadowing Using Multimission Measurements of Phase Space Density. JOURNAL OF GEOPHYSICAL RESEARCH. SPACE PHYSICS 2022; 127:e2021JA029298. [PMID: 35864842 PMCID: PMC9286781 DOI: 10.1029/2021ja029298] [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: 03/01/2021] [Revised: 12/21/2021] [Accepted: 01/10/2022] [Indexed: 06/15/2023]
Abstract
Loss mechanisms act independently or in unison to drive rapid loss of electrons in the radiation belts. Electrons may be lost by precipitation into the Earth's atmosphere, or through the magnetopause into interplanetary space-a process known as magnetopause shadowing. While magnetopause shadowing is known to produce dropouts in electron flux, it is unclear if shadowing continues to remove particles in tandem with electron acceleration processes, limiting the overall flux increase. We investigated the contribution of shadowing to overall radiation belt fluxes throughout a geomagnetic storm starting on the 7 September 2017. We use new, multimission phase space density calculations to decipher electron dynamics during each storm phase and identify features of magnetopause shadowing during both the net-loss and the net-acceleration storm phases on sub-hour time scales. We also highlight two distinct types of shadowing; "direct," where electrons are lost as their orbit intersects the magnetopause, and "indirect," where electrons are lost through ULF wave driven radial transport toward the magnetopause boundary.
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Affiliation(s)
- F. A. Staples
- Mullard Space Science LaboratoryUniversity College LondonLondonUK
| | - A. Kellerman
- Department of Earth, Planetary, and Space SciencesUniversity of CaliforniaLos AngelesCAUSA
| | | | - I. J. Rae
- Northumbria UniversityNewcastle upon TyneUK
| | | | - C. Forsyth
- Mullard Space Science LaboratoryUniversity College LondonLondonUK
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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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Strong whistler mode waves observed in the vicinity of Jupiter's moons. Nat Commun 2018; 9:3131. [PMID: 30087326 PMCID: PMC6081473 DOI: 10.1038/s41467-018-05431-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2017] [Accepted: 06/28/2018] [Indexed: 11/09/2022] Open
Abstract
Understanding of wave environments is critical for the understanding of how particles are accelerated and lost in space. This study shows that in the vicinity of Europa and Ganymede, that respectively have induced and internal magnetic fields, chorus wave power is significantly increased. The observed enhancements are persistent and exceed median values of wave activity by up to 6 orders of magnitude for Ganymede. Produced waves may have a pronounced effect on the acceleration and loss of particles in the Jovian magnetosphere and other astrophysical objects. The generated waves are capable of significantly modifying the energetic particle environment, accelerating particles to very high energies, or producing depletions in phase space density. Observations of Jupiter’s magnetosphere provide a unique opportunity to observe how objects with an internal magnetic field can interact with particles trapped in magnetic fields of larger scale objects. Observations of Jupiter’s magnetosphere provide opportunities to understand how magnetic fields interact with particles. Here, the authors report that the chorus wave power is increased in the vicinity of Europa and Ganymede. The generated waves are able to accelerate particles to very high energy.
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Cao X, Shprits YY, Ni B, Zhelavskaya IS. Scattering of Ultra-relativistic Electrons in the Van Allen Radiation Belts Accounting for Hot Plasma Effects. Sci Rep 2017; 7:17719. [PMID: 29255219 PMCID: PMC5735156 DOI: 10.1038/s41598-017-17739-7] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2017] [Accepted: 11/29/2017] [Indexed: 11/09/2022] Open
Abstract
Electron flux in the Earth's outer radiation belt is highly variable due to a delicate balance between competing acceleration and loss processes. It has been long recognized that Electromagnetic Ion Cyclotron (EMIC) waves may play a crucial role in the loss of radiation belt electrons. Previous theoretical studies proposed that EMIC waves may account for the loss of the relativistic electron population. However, recent observations showed that while EMIC waves are responsible for the significant loss of ultra-relativistic electrons, the relativistic electron population is almost unaffected. In this study, we provide a theoretical explanation for this discrepancy between previous theoretical studies and recent observations. We demonstrate that EMIC waves mainly contribute to the loss of ultra-relativistic electrons. This study significantly improves the current understanding of the electron dynamics in the Earth's radiation belt and also can help us understand the radiation environments of the exoplanets and outer planets.
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Affiliation(s)
- Xing Cao
- Department of Space Physics, School of Electronic Information, Wuhan University, Wuhan, China.
- Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Potsdam, Germany.
| | - Yuri Y Shprits
- Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Potsdam, Germany
- Institute of Physics and Astronomy, University of Potsdam, Potsdam, Germany
- Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California, USA
| | - Binbin Ni
- Department of Space Physics, School of Electronic Information, Wuhan University, Wuhan, China.
| | - Irina S Zhelavskaya
- Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Potsdam, Germany
- Institute of Physics and Astronomy, University of Potsdam, Potsdam, Germany
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Wave-induced loss of ultra-relativistic electrons in the Van Allen radiation belts. Nat Commun 2016; 7:12883. [PMID: 27678050 PMCID: PMC5052794 DOI: 10.1038/ncomms12883] [Citation(s) in RCA: 103] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2016] [Accepted: 08/10/2016] [Indexed: 11/08/2022] Open
Abstract
The dipole configuration of the Earth's magnetic field allows for the trapping of highly energetic particles, which form the radiation belts. Although significant advances have been made in understanding the acceleration mechanisms in the radiation belts, the loss processes remain poorly understood. Unique observations on 17 January 2013 provide detailed information throughout the belts on the energy spectrum and pitch angle (angle between the velocity of a particle and the magnetic field) distribution of electrons up to ultra-relativistic energies. Here we show that although relativistic electrons are enhanced, ultra-relativistic electrons become depleted and distributions of particles show very clear telltale signatures of electromagnetic ion cyclotron wave-induced loss. Comparisons between observations and modelling of the evolution of the electron flux and pitch angle show that electromagnetic ion cyclotron waves provide the dominant loss mechanism at ultra-relativistic energies and produce a profound dropout of the ultra-relativistic radiation belt fluxes.
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Hartley DP, Chen Y, Kletzing CA, Denton MH, Kurth WS. Applying the cold plasma dispersion relation to whistler mode chorus waves: EMFISIS wave measurements from the Van Allen Probes. JOURNAL OF GEOPHYSICAL RESEARCH. SPACE PHYSICS 2015; 120:1144-1152. [PMID: 26167444 PMCID: PMC4497456 DOI: 10.1002/2014ja020808] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2014] [Accepted: 01/20/2015] [Indexed: 05/17/2023]
Abstract
Most theoretical wave models require the power in the wave magnetic field in order to determine the effect of chorus waves on radiation belt electrons. However, researchers typically use the cold plasma dispersion relation to approximate the magnetic wave power when only electric field data are available. In this study, the validity of using the cold plasma dispersion relation in this context is tested using Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) observations of both the electric and magnetic spectral intensities in the chorus wave band (0.1-0.9 fce). Results from this study indicate that the calculated wave intensity is least accurate during periods of enhanced wave activity. For observed wave intensities >10-3 nT2, using the cold plasma dispersion relation results in an underestimate of the wave intensity by a factor of 2 or greater 56% of the time over the full chorus wave band, 60% of the time for lower band chorus, and 59% of the time for upper band chorus. Hence, during active periods, empirical chorus wave models that are reliant on the cold plasma dispersion relation will underestimate chorus wave intensities to a significant degree, thus causing questionable calculation of wave-particle resonance effects on MeV electrons.
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Affiliation(s)
- D P Hartley
- Physics Department, Lancaster UniversityLancaster, UK
| | - Y Chen
- Los Alamos National LaboratoryLos Alamos, New Mexico, USA
| | - C A Kletzing
- Department of Physics and Astronomy, University of IowaIowa City, Iowa, USA
| | - M H Denton
- Space Science InstituteBoulder, Colorado, USA
| | - W S Kurth
- Department of Physics and Astronomy, University of IowaIowa City, Iowa, USA
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Tu W, Elkington SR, Li X, Liu W, Bonnell J. Quantifying radial diffusion coefficients of radiation belt electrons based on global MHD simulation and spacecraft measurements. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2012ja017901] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Schiller Q, Li X, Koller J, Godinez H, Turner DL. A parametric study of the source rate for outer radiation belt electrons using a Kalman filter. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2012ja017779] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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