Are energetic electrons in the solar wind the source of the outer radiation belt?

Li, Xinlin; Baker, D. N.; Temerin, M.; Larson, D. E.; Lin, R. P.; Reeves, G. D.; Looper, M. D.; Kanekal, S.; Mewaldt, R. A.

doi:10.1029/97gl00543

Cited by 111 publications

(86 citation statements)

References 10 publications

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“…It is well known that the enhancements of energetic electrons in the outer radiation belt are correlated with solar wind speed (see, e.g. Paulikas andBlake, 1979 andLi et al, 1997). The similar relation found between electron fluxes in the HLPS and solar wind speed suggests that these electrons are related to the energetic electrons in the outer radiation belt.…”

Section: Discussionsupporting

confidence: 57%

Energetic particle fluxes in the exterior cusp and the high-latitude dayside magnetosphere: statistical results from the Cluster/RAPID instrument

Asikainen

Мурсула

2005

Ann. Geophys.

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Abstract. In this paper we study the fluxes of energetic protons (30-4000 keV) and electrons (20-400 keV) in the exterior cusp and in the adjacent high-latitude dayside plasma sheet (HLPS) with the Cluster/RAPID instrument. Using two sample orbits we demonstrate that the Cluster observations at high latitudes can be dramatically different because the satellite orbit traverses different plasma regions for different external conditions. We make a statistical study of energetic particles in the exterior cusp and HLPS by analysing all outbound Cluster dayside passes in February and March, 2002 and 2003. The average particle fluxes in HLPS are roughly three (protons) or ten (electrons) times larger than in the exterior cusp. This is also true on those Cluster orbits where both regions are visited within a short time interval. Moreover, the total electron fluxes, as well as proton fluxes above some 100 keV, in these two regions correlate with each other. This is true even for fluxes in every energy channel when considered separately. The spectral indices of electron and proton fluxes are the same in the two regions. We also examine the possible dependence of particle fluxes at different energies on the external (solar wind and IMF) and internal (geomagnetic) conditions. The energetic proton fluxes (but not electron fluxes) in the cusp behave differently at low and high energies. At low energies (<70 keV), the fluxes increase strongly with the magnitude of IMF B y . Instead, at higher energies the proton fluxes in the cusp depend on substorm/geomagnetic activity. In HLPS proton fluxes, irrespective of energy, depend strongly on the K p and AE indices. The electron fluxes in HLPS depend both on the K p index and the solar wind speed. In the cusp the electron fluxes mainly depend on the solar wind speed, and are higher for northward than southward IMF. These results give strong evidence in favour of the idea that the high-latitude dayside plasma sheet is the main source of energetic particles in the exterior cusp. Energetic particles can reach HLPS from the near-Earth tail. The closed field lines of HLPS actCorrespondence to: T. Asikainen (timo.asikainen@oulu.fi) as storage for these particles. Direct diffusion (for electrons and high-energy protons) and magnetic reconnection in the high-latitude magnetopause near HLPS (for low energy protons) control the number of particles released into the exterior cusp. Note that this explanation, in contrast to other suggested theories, works both for the energetic protons and electrons in the exterior cusp.

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Section: Discussionsupporting

confidence: 57%

Energetic particle fluxes in the exterior cusp and the high-latitude dayside magnetosphere: statistical results from the Cluster/RAPID instrument

Asikainen

Мурсула

2005

Ann. Geophys.

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“…The satellite crosses the outer radiation belt at relatively high magnetic latitude, near the loss cone. Therefore, mostly energetic electrons of large equatorial pitch angle were observed (Li et al, 1997). The data collected have been averaged and sorted by L shell.…”

Section: Data Sets and Their Analysismentioning

confidence: 99%

Association of radiation belt electron enhancements with earthward penetration of Pc5 ULF waves: a case study of intense 2001 magnetic storms

et al. 2015

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Abstract. Geospace magnetic storms, driven by the solar wind, are associated with increases or decreases in the fluxes of relativistic electrons in the outer radiation belt. We examine the response of relativistic electrons to four intense magnetic storms, during which the minimum of the Dst index ranged from −105 to −387 nT, and compare these with concurrent observations of ultra-low-frequency (ULF) waves from the trans-Scandinavian IMAGE magnetometer network and stations from multiple magnetometer arrays available through the worldwide SuperMAG collaboration. The latitudinal and global distribution of Pc5 wave power is examined to determine how deep into the magnetosphere these waves penetrate. We then investigate the role of Pc5 wave activity deep in the magnetosphere in enhancements of radiation belt electrons population observed in the recovery phase of the magnetic storms. We show that, during magnetic storms characterized by increased post-storm electron fluxes as compared to their pre-storm values, the earthward shift of peak and inner boundary of the outer electron radiation belt follows the Pc5 wave activity, reaching L shells as low as 3-4. In contrast, the one magnetic storm characterized by irreversible loss of electrons was related to limited Pc5 wave activity that was not intensified at low L shells. These observations demonstrate that enhanced Pc5 ULF wave activity penetrating deep into the magnetosphere during the main and recovery phase of magnetic storms can, for the cases examined, distinguish storms that resulted in increases in relativistic electron fluxes in the outer radiation belts from those that did not.

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“…In other active periods the enhanced¯uxes of energetic electrons (0.7±3.0 MeV) at v $ 4±5 probably are not a result of diusion from higher v shells (Selesnick and Blake, 1998), which determines the spatial distribution during quiet periods. Additionally, an analysis of the November 3±4, 1993 high-speed solar wind stream event showed that the phase space density in the solar wind is insucient to explain the increase of relativistic outer radiation belt electrons (Li et al, 1997). Therefore, enhancement in the high energy electron¯uxes at lower L-Shells (Paulikas and Blake, 1979) indicates a possible existence of additional processes which operate at this region where a local heating mechanism may be operative for relativistic electrons.…”

Section: Introductionmentioning

confidence: 99%

Resonant enhancement of relativistic electron fluxes during geomagnetically active periods

1999

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Abstract. The strong increase in the¯ux of relativistic electrons during the recovery phase of magnetic storms and during other active periods is investigated with the help of Hamiltonian formalism and simulations of test electrons which interact with whistler waves. The intensity of the whistler waves is enhanced signi®cantly due to injection of 10±100 keV electrons during the substorm. Electrons which drift in the gradient and curvature of the magnetic ®eld generate the rising tones of VLF whistler chorus. The seed population of relativistic electrons which bounce along the inhomogeneous magnetic ®eld, interacts resonantly with the whistler waves. Whistler wave propagating obliquely to the magnetic ®eld can interact with energetic electrons through Landau, cyclotron, and higher harmonic resonant interactions when the Doppler-shifted wave frequency equals any (positive or negative) integer multiple of the local relativistic gyrofrequency. Because the gyroradius of a relativistic electron may be the order of or greater than the perpendicular wavelength, numerous cyclotron, harmonics can contribute to the resonant interaction which breaks down the adiabatic invariant. A similar process diuses the pitch angle leading to electron precipitation. The irreversible changes in the adiabatic invariant depend on the relative phase between the wave and the electron, and successive resonant interactions result in electrons undergoing a random walk in energy and pitch angle. This resonant process may contribute to the 10±100 fold increase of the relativistic electron¯ux in the outer radiation belt, and constitute an interesting relation between substorm-generated waves and enhancements in¯uxes of relativistic electrons during geomagnetic storms and other active periods.

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Are energetic electrons in the solar wind the source of the outer radiation belt?

Cited by 111 publications

References 10 publications

Energetic particle fluxes in the exterior cusp and the high-latitude dayside magnetosphere: statistical results from the Cluster/RAPID instrument

Energetic particle fluxes in the exterior cusp and the high-latitude dayside magnetosphere: statistical results from the Cluster/RAPID instrument

Association of radiation belt electron enhancements with earthward penetration of Pc5 ULF waves: a case study of intense 2001 magnetic storms

Resonant enhancement of relativistic electron fluxes during geomagnetically active periods

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