Energetic electron precipitation from the inner zone

Abel, Bob; Thorne, R. M.; Vampola, A. L.

doi:10.1029/97gl02055

Cited by 12 publications

(7 citation statements)

References 20 publications

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“…Hess [] summarized the limited existing inner zone pre‐Starfish event results as showing that the “…spectrum is flat for 100 < Ee < 400 keV” and “… not certain whether there are any electrons present of E > 800 keV.” More recently, Abel et al . [, ] presented spectra of equatorially mirroring electrons for a few L values based on the CRRES Magnetic Electron Spectrometer A [ Vampola et al ., ] data. These showed relatively soft spectra for energies >500 keV and are discussed more below.…”

Section: Introductionmentioning

confidence: 99%

Van Allen Probes show that the inner radiation zone contains no MeV electrons: ECT/MagEIS data

Fennell¹,

Claudepierre²,

Blake³

et al. 2015

Geophysical Research Letters

119

132

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We present Van Allen Probe observations of electrons in the inner radiation zone. The measurements were made by the Energetic Particle, Composition, and Thermal Plasma/Magnetic Electron Ion Spectrometer (MagEIS) sensors that were designed to measure electrons with the ability to remove unwanted signals from penetrating protons, providing clean measurements. No electrons >900 keV were observed with equatorial fluxes above background (i.e., >0.1 el/(cm 2 s sr keV)) in the inner zone. The observed fluxes are compared to the AE9 model and CRRES observations. Electron fluxes <200 keV exceeded the AE9 model 50% fluxes and were lower than the higher-energy model fluxes. Phase space density radial profiles for 1.3 ≤ L* < 2.5 had mostly positive gradients except near L*~2.1, where the profiles for μ = 20-30 MeV/G were flat or slightly peaked. The major result is that MagEIS data do not show the presence of significant fluxes of MeV electrons in the inner zone while current radiation belt models and previous publications do.

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Section: Introductionmentioning

confidence: 99%

Van Allen Probes show that the inner radiation zone contains no MeV electrons: ECT/MagEIS data

Fennell¹,

Claudepierre²,

Blake³

et al. 2015

Geophysical Research Letters

119

132

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“…[2] The coupling between the magnetosphere and the ionosphere through precipitating particles from radiation belts and the central plasma sheet that strongly controls ionization and conductance in the ionosphere has been known for some time, although it is one of the most difficult couplings to understand [e.g., Paulikas, 1975;Buonsanto, 1999;Ma et al, 2008;Kelley, 2009]. The energy deposition of precipitating particles of various energies mainly through the ionization of atmospheric atoms occurs at different altitudes, particularly within the D, E, and F regions of the ionosphere and extends from high to midlatitudes and over the South-Atlantic Anomaly (SAA) at low latitudes [e.g., Voss and Smith, 1980;Vampola and Gorney, 1983;Rees et al, 1988;Abel et al, 1997]. An impact of precipitating particles in the lower ionosphere (the D and E layers) and the upper atmosphere in terms of enhanced ionization and other related aeronomical effects has been investigated in a large number of studies [e.g., Buonsanto, 1999, and references therein;Nishino et al, 2002;Peter et al, 2006;Clilverd et al, 2008Clilverd et al, , 2010Turunen et al, 2009;Lam et al, 2010;Dmitriev et al, 2011], while evidence for ionospheric signatures in the topside ionosphere (F region) in the midlatitudes and over the SAA at low latitudes have also been reported [e.g., Foster et al, 1994Foster et al, , 1998Abdu et al, 2005;Kunitsyn et al, 2008aKunitsyn et al, , 2008bDmitriev and Yeh, 2008;Pedatella et al, 2009;Ngwira et al, 2012].…”

Section: Introductionmentioning

confidence: 99%

TEC evidence for near‐equatorial energy deposition by 30 keV electrons in the topside ionosphere

et al. 2013

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[1] Observations of energetic electrons (10 -300 keV) by NOAA/POES and DMSP satellites at heights <1000 km during the period from 1999 to 2010 allowed finding abnormal intense fluxes of~10 6 -10 7 cm À2 s À1 sr À1 for quasi-trapped electrons appearing within the forbidden zone of low latitudes over the African, Indo-China, and Pacific regions. Extreme fluxes appeared often in the early morning and persisted for several hours during the maximum and recovery phase of geomagnetic storms. We analyzed nine storm time events when extreme electron fluxes first appeared in the Eastern Hemisphere, then drifted further eastward toward the South-Atlantic Anomaly. Using the electron spectra, we estimated the possible ionization effect produced by quasi-trapped electrons in the topside ionosphere. The estimated ionization was found to be large enough to satisfy observed storm time increases in the ionospheric total electron content (TEC) determined for the same spatial and temporal ranges from global ionospheric maps. Additionally, extreme fluxes of quasi-trapped electrons were accompanied by the significant elevation of the low-latitude F-layer obtained from COSMIC/FORMOSAT-3 radio occultation measurements. We suggest that the storm time ExB drift of energetic electrons from the inner radiation belt is an important driver of positive ionospheric storms within low-latitude and equatorial regions.

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“…The very low likelihood of events potentially leading to direct injection or radial diffusion of relativistic electrons into the inner belt supports the conjecture of Kim and Shprits [2012] that any negative gradient in the phase space density of ≈ 0.5-1 MeV electrons toward higher L in the region L ∼ 1.5-2 [e.g., see Abel et al, 1997;Kim and Shprits, 2012;Fennell et al, 2015] would result either from very rare intrusions followed by very long periods (∼ year) dominated by losses to the atmosphere stronger at higher L in this region or from a local acceleration of lower energy (∼ 100 keV) electrons via resonant scattering by lightning-generated and VLF waves peaking near L = 1.5 − 1.7. However, energy diffusion by whistler-mode waves would require years to produce such a flux maximum .…”

Section: Discussionmentioning

confidence: 52%

Approximate analytical formulation of radial diffusion and whistler‐induced losses from a preexisting flux peak in the plasmasphere

2015

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Modeling the spatiotemporal evolution of relativistic electron fluxes trapped in the Earth's radiation belts in the presence of radial diffusion coupled with wave‐induced losses should address one important question: how deep can relativistic electrons penetrate into the inner magnetosphere? However, a full modeling requires extensive numerical simulations solving the comprehensive quasi‐linear equations describing pitch angle and radial diffusion of the electron distribution, making it rather difficult to perform parametric studies of the flux behavior. Here we consider the particular situation where a localized flux peak (or storage ring) has been produced at low L < 4 during a period of strong disturbances, through a combination of chorus‐induced energy diffusion (or direct injection) at low L together with enhanced wave‐induced losses and outward radial transport at higher L. Assuming that radial diffusion can be further described as the spatial broadening within the plasmasphere of this preexisting flux peak, simple approximate analytical solutions for the distribution of trapped relativistic electrons are derived. Such a simplified formalism provides a convenient means for easily determining whether radial diffusion actually prevails over atmospheric losses at any particular time for given electron energy E and location L. It is further used to infer favorable conditions for relativistic electron access to the inner belt, providing an explanation for the relative scarcity of such a feat under most circumstances. Comparisons with electron flux measurements on board the Van Allen Probes show a reasonable agreement between a few weeks and 4 months after the formation of a flux peak.

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Energetic electron precipitation from the inner zone

Cited by 12 publications

References 20 publications

Van Allen Probes show that the inner radiation zone contains no MeV electrons: ECT/MagEIS data

Van Allen Probes show that the inner radiation zone contains no MeV electrons: ECT/MagEIS data

TEC evidence for near‐equatorial energy deposition by 30 keV electrons in the topside ionosphere

Approximate analytical formulation of radial diffusion and whistler‐induced losses from a preexisting flux peak in the plasmasphere

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