Correlated Effects of Energetic Electrons at the 6.6 <i>R<sub>e</sub></i> Equator and the Auroral Zone During Magnetospheric Substorms

Parks, G. K.; Arnoldy, R. L.; Lezniak, T. W.; Winckler, J. R.

doi:10.1002/rds196837715

Cited by 39 publications

(13 citation statements)

References 10 publications

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“…Note that the second injection pulse was also closely accompanied by a large increase in the NAR riometer intensity. Hence the ground-based riometer trace mirrors almost precisely the shape of the equatorial flux profile measured for electrons on the conjugate field line [see Parks et al, 1968;Rosen and Winckler, 1970].…”

Section: Moderate Precipitation Eventsmentioning

confidence: 76%

Near‐equatorial, high‐resolution measurements of electron precipitation at L ≃6.6

Baker¹,

Stauning²,

Hones³

et al. 1981

J. Geophys. Res.

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Previous studies of precipitating electrons at low altitudes in the auroral zone have shown that such precipitation is impulsive and highly fluctuating (time scales of seconds). It is also generally supposed that energetic electron precipitation results from wave‐particle scattering that occurs primarily near the outer zone (L=5‐8) equatorial plane. In contrast to prior low‐altitude measurements, however, nearly all previously reported measurements made in the near‐equatorial regions have been quite slow, with loss cone sampling times of minutes. This paper presents correlated measurements of Technical University of Denmark auroral zone riometer data (20‐s sampling times) and Los Alamos Scientific Laboratory high‐resolution (8‐ms sampling, 10‐s rotation) >30‐keV electron measurements made at geostationary orbit during the course of magnetospheric substorms. Prior to substorm expansion onset, substantial evidence is found to support the concept of a substorm growth phase. Following the expansion phase onset and the concomitant injection of newly energized electrons into the outer magnetosphere, it is possible to examine equatorial electron fluxes in the loss cone for cases of weak pitch angle diffusion as well as for cases of strong pitch angle diffusion. During strong diffusion events, it is found that precipitating electron fluxes are highly fluctuating and impulsive at the minimum loss cone sampling time of 10 s. For such event periods the pitch angle distribution outside the loss cone is nearly flat (isotropic flux), the absolute electron intensity (>30 keV) is near ‘saturation’ (j ∼5 × 10 7 cm −2 s −1 sr −1), and the 20‐MHz conjugate riometer intensity is very high (5–15 dB). These results demonstrate that equatorial wave‐particle interactions do not build up steadily and gradually but rather that they develop in an impulsive or sporadic way. Thus these observations are quite consistent with low‐altitude results and probably relate equatorial phenomena to such ionspheric phenomena as pulsating aurora and fluctuating auroral zone bremsstrahlung X rays.

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Section: Moderate Precipitation Eventsmentioning

confidence: 76%

Near‐equatorial, high‐resolution measurements of electron precipitation at L ≃6.6

Baker¹,

Stauning²,

Hones³

et al. 1981

J. Geophys. Res.

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“…Studies conducted have shown a broad correlation between geosynchronous electron flux intensity and CNA during substorms (e.g. Parks et al, 1968;Arnoldy and Chan, 1969;Rosen and Winckler, 1970). Baker et al (1981) present a number of events where riometers record CNA rises at the time of geosynchronous flux intensity increases at conjugate LANL satellites during the near midnight and morning sectors, again during substorms.…”

Section: Precipitation Following the Substorm Activitymentioning

confidence: 99%

The driving mechanisms of particle precipitation during the moderate geomagnetic storm of 7 January 2005

et al. 2007

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Abstract. The arrival of an interplanetary coronal mass ejection (ICME) triggered a sudden storm commencement (SSC) at ∼09:22 UT on the 7 January 2005. The ICME followed a quiet period in the solar wind and interplanetary magnetic field (IMF). We present global scale observations of energetic electron precipitation during the moderate geomagnetic storm driven by the ICME. Energetic electron precipitation is inferred from increases in cosmic noise absorption (CNA) recorded by stations in the Global Riometer Array (GLO-RIA). No evidence of CNA was observed during the first four hours of passage of the ICME or following the sudden commencement (SC) of the storm. This is consistent with the findings of Osepian and Kirkwood (2004) that SCs will only trigger precipitation during periods of geomagnetic activity or when the magnetic perturbation in the magnetosphere is substantial. CNA was only observed following enhanced coupling between the IMF and the magnetosphere, resulting from southward oriented IMF. Precipitation was observed due to substorm activity, as a result of the initial injection and particles drifting from the injection region. During the recovery phase of the storm, when substorm activity diminished, precipitation due to density driven increases in the solar wind dynamic pressure (P dyn ) were identified. A number of increases in P dyn were shown to drive sudden impulses (SIs) in the geomagnetic field. While many of these SIs appear coincident with CNA, SIs without CNA were also observed. During this period, the threshold of geomagnetic activity required for SC driven precipitation was exceeded. This implies that solar wind density driven SIs occurring during storm recovery can drive a different response in particle precipitation to typical SCs.

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“…[2] The acceleration of charged particles to suprathermal energies and the resulting flux increases of high-energy particles are a major consequence of space plasma activity and magnetic reconfiguration. Energetic particle events in the Earth's magnetotail (injections) are typically associated with magnetospheric substorms [e.g., Parks et al, 1968;Lezniak et al, 1968;Arnoldy and Chan, 1969;Baker et al, 1978;Belian et al, 1981] or, more generally, dipolarization events [e.g., Nakamura et al, 2002;Runov et al, 2009;Sergeev et al, 2009;Deng et al, 2010], characterized by a rapid change from stretched, tail-like to more dipolar magnetic fields. Dipolarization events may involve a brief earthward moving dipolarization pulse or "dipolarization front" [e.g., Nakamura et al, 2002;Runov et al, 2009;Sergeev et al, 2009] or, typically closer to Earth, an increase of B z toward a more persistent higher level .…”

Section: Introductionmentioning

confidence: 99%

Particle acceleration in dipolarization events

et al. 2013

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[1] Using the electromagnetic fields of a recent MHD simulation of magnetotail reconnection, flow bursts and dipolarization, we investigate the acceleration of test particles (protons and electrons) to suprathermal energies, confirming and extending earlier results on acceleration mechanisms and sources. (Part of the new results have been reviewed recently in Birn et al., Space Science Reviews, 167, doi:10.1007/ s11214-012-9874-4.) The test particle simulations reproduce major features of energetic particle events (injections) associated with substorms or other dipolarization events, particularly a rapid rise of energetic particle fluxes over limited ranges of energy. The major acceleration mechanisms for electrons are betatron acceleration and Fermi acceleration in the collapsing magnetic field. Ions, although non-adiabatic, undergo similar acceleration. Two major entry mechanisms into the acceleration site are identified: cross-tail drift from the inner tail plasma sheet and reconnection entry from field lines extending to the more distant plasma sheet. The former dominates early in an event and at higher energies (hundreds of keV) while the latter constitutes the main source later and at lower energies (tens of keV). Despite the fact that the injection front moves earthward in the tail, the peak of energetic particle fluxes moves to higher latitude when mapped from the near-Earth boundary to Earth in a static magnetic field model.

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Correlated Effects of Energetic Electrons at the 6.6 R_e Equator and the Auroral Zone During Magnetospheric Substorms

Cited by 39 publications

References 10 publications

Near‐equatorial, high‐resolution measurements of electron precipitation at L ≃6.6

Near‐equatorial, high‐resolution measurements of electron precipitation at L ≃6.6

The driving mechanisms of particle precipitation during the moderate geomagnetic storm of 7 January 2005

Particle acceleration in dipolarization events

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Correlated Effects of Energetic Electrons at the 6.6 Re Equator and the Auroral Zone During Magnetospheric Substorms

Cited by 39 publications

References 10 publications

Near‐equatorial, high‐resolution measurements of electron precipitation at L ≃6.6

Near‐equatorial, high‐resolution measurements of electron precipitation at L ≃6.6

The driving mechanisms of particle precipitation during the moderate geomagnetic storm of 7 January 2005

Particle acceleration in dipolarization events

Contact Info

Product

Resources

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Correlated Effects of Energetic Electrons at the 6.6 R_e Equator and the Auroral Zone During Magnetospheric Substorms