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Reeves GD, Friedel RHW, Larsen BA, Skoug RM, Funsten HO, Claudepierre SG, Fennell JF, Turner DL, Denton MH, Spence HE, Blake JB, Baker DN. Energy-dependent dynamics of keV to MeV electrons in the inner zone, outer zone, and slot regions. J Geophys Res Space Phys 2016; 121:397-412. [PMID: 27818855 PMCID: PMC5070526 DOI: 10.1002/2015ja021569] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2015] [Revised: 12/18/2015] [Accepted: 12/22/2015] [Indexed: 06/01/2023]
Abstract
We present observations of the radiation belts from the Helium Oxygen Proton Electron and Magnetic Electron Ion Spectrometer particle detectors on the Van Allen Probes satellites that illustrate the energy dependence and L shell dependence of radiation belt enhancements and decays. We survey events in 2013 and analyze an event on 1 March in more detail. The observations show the following: (a) at all L shells, lower energy electrons are enhanced more often than higher energies; (b) events that fill the slot region are more common at lower energies; (c) enhancements of electrons in the inner zone are more common at lower energies; and (d) even when events do not fully fill the slot region, enhancements at lower energies tend to extend to lower L shells than higher energies. During enhancement events the outer zone extends to lower L shells at lower energies while being confined to higher L shells at higher energies. The inner zone shows the opposite with an outer boundary at higher L shells for lower energies. Both boundaries are nearly straight in log(energy) versus L shell space. At energies below a few 100 keV, radiation belt electron penetration through the slot region into the inner zone is commonplace, but the number and frequency of "slot filling" events decreases with increasing energy. The inner zone is enhanced only at energies that penetrate through the slot. Energy- and L shell-dependent losses (that are consistent with whistler hiss interactions) return the belts to more quiescent conditions.
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Affiliation(s)
- Geoffrey D Reeves
- Space Science and Applications Group Los Alamos National Laboratory Los Alamos New Mexico USA; The New Mexico Consortium Los Alamos New Mexico USA
| | - Reiner H W Friedel
- Space Science and Applications Group Los Alamos National Laboratory Los Alamos New Mexico USA; The New Mexico Consortium Los Alamos New Mexico USA
| | - Brian A Larsen
- Space Science and Applications Group Los Alamos National Laboratory Los Alamos New Mexico USA; The New Mexico Consortium Los Alamos New Mexico USA
| | - Ruth M Skoug
- Space Science and Applications Group Los Alamos National Laboratory Los Alamos New Mexico USA
| | - Herbert O Funsten
- Space Science and Applications Group Los Alamos National Laboratory Los Alamos New Mexico USA
| | | | | | - Drew L Turner
- The Aerospace Corporation Los Angeles California USA
| | | | - Harlan E Spence
- Institute for the Study of Earth, Oceans, and Space and Department of Physics University of New Hampshire Durham New Hampshire USA
| | | | - Daniel N Baker
- Laboratory for Atmospheric and Space Physics University of Colorado Boulder Boulder Colorado USA
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Reeves GD, Spence HE, Henderson MG, Morley SK, Friedel RHW, Funsten HO, Baker DN, Kanekal SG, Blake JB, Fennell JF, Claudepierre SG, Thorne RM, Turner DL, Kletzing CA, Kurth WS, Larsen BA, Niehof JT. Electron acceleration in the heart of the Van Allen radiation belts. Science 2013; 341:991-4. [PMID: 23887876 DOI: 10.1126/science.1237743] [Citation(s) in RCA: 403] [Impact Index Per Article: 36.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The Van Allen radiation belts contain ultrarelativistic electrons trapped in Earth's magnetic field. Since their discovery in 1958, a fundamental unanswered question has been how electrons can be accelerated to such high energies. Two classes of processes have been proposed: transport and acceleration of electrons from a source population located outside the radiation belts (radial acceleration) or acceleration of lower-energy electrons to relativistic energies in situ in the heart of the radiation belts (local acceleration). We report measurements from NASA's Van Allen Radiation Belt Storm Probes that clearly distinguish between the two types of acceleration. The observed radial profiles of phase space density are characteristic of local acceleration in the heart of the radiation belts and are inconsistent with a predominantly radial acceleration process.
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Affiliation(s)
- G D Reeves
- Space Science and Applications Group, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
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Baker DN, Kanekal SG, Hoxie VC, Henderson MG, Li X, Spence HE, Elkington SR, Friedel RHW, Goldstein J, Hudson MK, Reeves GD, Thorne RM, Kletzing CA, Claudepierre SG. A long-lived relativistic electron storage ring embedded in Earth's outer Van Allen belt. Science 2013; 340:186-90. [PMID: 23450000 DOI: 10.1126/science.1233518] [Citation(s) in RCA: 189] [Impact Index Per Article: 17.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Since their discovery more than 50 years ago, Earth's Van Allen radiation belts have been considered to consist of two distinct zones of trapped, highly energetic charged particles. The outer zone is composed predominantly of megaelectron volt (MeV) electrons that wax and wane in intensity on time scales ranging from hours to days, depending primarily on external forcing by the solar wind. The spatially separated inner zone is composed of commingled high-energy electrons and very energetic positive ions (mostly protons), the latter being stable in intensity levels over years to decades. In situ energy-specific and temporally resolved spacecraft observations reveal an isolated third ring, or torus, of high-energy (>2 MeV) electrons that formed on 2 September 2012 and persisted largely unchanged in the geocentric radial range of 3.0 to ~3.5 Earth radii for more than 4 weeks before being disrupted (and virtually annihilated) by a powerful interplanetary shock wave passage.
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Affiliation(s)
- D N Baker
- Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA.
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Reeves GD, Morley SK, Friedel RHW, Henderson MG, Cayton TE, Cunningham G, Blake JB, Christensen RA, Thomsen D. On the relationship between relativistic electron flux and solar wind velocity: Paulikas and Blake revisited. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2010ja015735] [Citation(s) in RCA: 125] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Geoffrey D. Reeves
- Space Science and Applications Group; Los Alamos National Laboratory; Los Alamos New Mexico USA
| | - Steven K. Morley
- Space Science and Applications Group; Los Alamos National Laboratory; Los Alamos New Mexico USA
| | - Reiner H. W. Friedel
- Space Science and Applications Group; Los Alamos National Laboratory; Los Alamos New Mexico USA
| | - Michael G. Henderson
- Space Science and Applications Group; Los Alamos National Laboratory; Los Alamos New Mexico USA
| | - Thomas E. Cayton
- Space Science and Applications Group; Los Alamos National Laboratory; Los Alamos New Mexico USA
| | - Gregory Cunningham
- Space Science and Applications Group; Los Alamos National Laboratory; Los Alamos New Mexico USA
| | | | - Rod A. Christensen
- Space Science and Applications Group; Los Alamos National Laboratory; Los Alamos New Mexico USA
| | - Davis Thomsen
- Space Science and Applications Group; Los Alamos National Laboratory; Los Alamos New Mexico USA
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Morley SK, Friedel RHW, Spanswick EL, Reeves GD, Steinberg JT, Koller J, Cayton T, Noveroske E. Dropouts of the outer electron radiation belt in response to solar wind stream interfaces: global positioning system observations. Proc Math Phys Eng Sci 2010. [DOI: 10.1098/rspa.2010.0078] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
We present a statistical study of relativistic electron counts in the electron radiation belt across a range of drift shells (L*>4) combining data from nine combined X-ray dosimeters (CXD) on the global positioning system (GPS) constellation. The response of the electron counts as functions of time, energy and drift shell are examined statistically for 67 solar wind stream interfaces (SIs); two-dimensional superposed epoch analysis is performed with the CXD data. For these epochs we study the radiation belt dropouts and concurrent variations in key geophysical parameters.
At higher L* we observe a tendency for a gradual drop in the electron counts over the day preceding the SI, consistent with outward diffusion and magnetopause shadowing. At all L*, dropouts occur with a median time scale of ≃7 h and median counts fall by 0.4–1.8 orders of magnitude. The central tendencies of radiation belt dropout and recovery depend on both L* and energy. For ≃70 per cent of epochs Sym-H more than −30 nT, yet only three of 67 SIs did not have an associated dropout in the electron data. Statistical maps of electron precipitation suggest that chorus-driven relativistic electron microbursts might be major contributors to radiation belt losses under high-speed stream driving.
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Affiliation(s)
- Steven K. Morley
- Space Science and Applications, Los Alamos National Laboratory, Los Alamos, NM, USA
| | - Reiner H. W. Friedel
- Space Science and Applications, Los Alamos National Laboratory, Los Alamos, NM, USA
| | - Emma L. Spanswick
- Space Science and Applications, Los Alamos National Laboratory, Los Alamos, NM, USA
- Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada
| | - Geoffrey D. Reeves
- Space Science and Applications, Los Alamos National Laboratory, Los Alamos, NM, USA
| | - John T. Steinberg
- Space Science and Applications, Los Alamos National Laboratory, Los Alamos, NM, USA
| | - Josef Koller
- Space Science and Applications, Los Alamos National Laboratory, Los Alamos, NM, USA
| | - Thomas Cayton
- Space Science and Applications, Los Alamos National Laboratory, Los Alamos, NM, USA
| | - Evan Noveroske
- Space Data Systems, Los Alamos National Laboratory, Los Alamos, NM, USA
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