Substorm associated magnetotail energetic electrons pitch angle evolutions and flow reversals: Cluster observation

Wu, Puxun; Fritz, T. A.; Larvaud, B.; Lucek, E.

doi:10.1029/2006gl026595

Cited by 43 publications

(77 citation statements)

References 29 publications

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“…It has been shown that adiabatic betatron acceleration and Fermi acceleration are the mechanisms that energize electrons during dipolarization (Li et al, 1998;Ashour-Abdalla et al, 2011;Fu et al, 2011). However, there are some studies showing that adiabatic heating alone cannot account for the observed energy gain during substorm (Wu et al, 2006) might play some roles in electron energization at the fronts (Zhou et al, 2009). Whistler waves observed here might be able to efficiently accelerate electrons.…”

Section: Discussionmentioning

confidence: 73%

Kinetic structure and wave properties associated with sharp dipolarization front observed by Cluster

et al. 2012

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Abstract. Multiple dipolarization fronts (DFs) were observed by Cluster spacecraft in the magnetotail during a substorm. These DFs were kinetic structures, embedded in the bursty plasma flow, and moved earthward (mainly) and dawnward. Intense electric field, parallel and perpendicular currents were detected in the DF layer. These front layers were energy dissipation region (load region) where the energy of electromagnetic fields were transferred to the plasma thermal and kinetic energy. This dissipation was dominated by electrons. There were enhancements of plasma waves around the DF region: wavelet results show that wave activities around the ion cyclotron frequency in the front layer were generated by Alfvén ion cyclotron instability; whistler waves were also detected before, during and after the DFs, which are triggered by electron temperature anisotropy and coincident with enhancement of energetic electron fluxes. The observation of these waves could be important for the understanding of evolution of DF and electron energization during the substorm. We discuss the generation mechanism of the DFs and suggest that these DFs were generated in the process of transient reconnection, and then traveled toward the Earth.

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Section: Discussionmentioning

confidence: 73%

Kinetic structure and wave properties associated with sharp dipolarization front observed by Cluster

et al. 2012

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“…It has been reported by De Michelis et al [1999] that the plasma anisotropy in the near-Earth tail region is more often found during geomagnetic active periods. Other observations and analyses on the plasma anisotropy also suggest that the perpendicular ion anisotropy after dipolarizations in substorms were mainly caused by betatron heating when the magnetic field strength is strongly enhanced [Smets et al, 1999;Wu et al, 2006]. This mechanism is similar to the mechanism that produces anisotropy for energetic ions in the inner magnetosphere where the betatron acceleration plays an important role to increase ion perpendicular temperature [Liu and Rostoker, 1995;Woch et al, 1988].…”

Section: Discussionmentioning

confidence: 73%

“…The dominant Fermi acceleration on electrons was also found in AMPTE Ion Release Module (IRM) observations between 10 and 15 R E in the magnetotail [Sergeev et al, 2001]. Wu et al [2006] used Cluster observations to show the evolution of magnetotail energetic electron pitch angle distributions during substorms. They proposed a model in which Fermi acceleration dominated for electrons that were accelerated from the reconnection region, while betatron acceleration dominated for electrons accelerated from the near-tail region (inside of 10 R E in tail).…”

Section: Spatial Scale Of Mirror Structures and Electron Distributionmentioning

confidence: 99%

“…Thus, these two excursions may be caused by the uncertainty of the difference between two large plasma beta values (b k,e and b ?,e ) and do not suggest firehose instability. The parallel-anisotropic distribution of electrons can be produced by Fermi acceleration when the configuration of magnetic field is significantly changed, especially when the magnetic field lines shorten during dipolarization [Smets et al, 1999;Sergeev et al, 2001;Wu et al, 2006]. Many authors have studied this type of electron parallel anisotropy with plasma measurements from different missions.…”

Section: Spatial Scale Of Mirror Structures and Electron Distributionmentioning

confidence: 99%

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Case studies of mirror-mode structures observed by THEMIS in the near-Earth tail during substorms

et al. 2011

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[1] An examination of the magnetic field and plasma observed by the inner THEMIS-D spacecraft (P3) close to the equatorial plane at ∼11R E at local midnight reveals the occurrence of mirror-mode structures. These structures have the same characteristic waveform seen in other regions. The examination of the mirror-mode instability shows that inside these structures the threshold of mirror instability is marginally reached, while the surrounding plasma is mirror stable. The observed mirror structures occur in the dipolarized magnetic field following a substorm-related dipolarization. It is found that after the dipolarization front, the local ions become more anisotropic and initial magnetic holes form inside this anisotropic plasma before the fully-fledged mirror structures are observed. The ions become less anisotropic afterward, but the strong field depression in the magnetic holes enhances the effective plasma beta so that the mirror instability threshold is marginally reached. Thus, the dipolarization process provides the large-amplitude magnetic field fluctuations and the anisotropic plasma environment for mirror structures to grow. The isolated large-amplitude mirror-mode structures survive in the mirror-stable plasma even through the plasma becomes less anisotropic. It is also found that the width of magnetotail mirror-structures is smaller than one gyroradius of a plasma sheet proton, which is different from the width of mirror structures in other regions. These mirror structures appear to have a strong correlation with electron anisotropy changes. These observations suggest that electron kinetics may also play a role during the growth and saturation of mirror instability in the near-Earth tail.

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“…However, surveys show that field-aligned electron fluxes occur only a few percent of the observing time and are concentrated in the midnight to dawn sectors of the plasma sheet [e.g., Hada et al, 1981;Klumpar, 1993;Sugiyama et al, 1997]. While some investigations suggested an auroral source for the fieldaligned distributions [e.g., Klumpar et al, 1988;Klumpar, 1993], the consensus had developed that such distributions arise either locally or remotely from Fermi-type acceleration [e.g., Hada et al, 1981;Smets et al, 1999;Shiokawa et al, 2003;Vogiatzis et al, 2006;Wu et al, 2006]. Field-aligned electron fluxes have certainly been observed in the Earth's magnetosphere at low altitudes above the aurora and associated with particle acceleration in field-aligned potentials [e.g., Carlson et al, 1998;Marklund et al, 2001].…”

Section: Introductionmentioning

confidence: 99%

Pitch angle distributions of energetic electrons at Saturn

et al. 2011

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[1] Pitch angle distributions of energetic electrons (110-365 keV) at Saturn are statistically analyzed for [2005][2006][2007][2008][2009]. Using a nondipolar model magnetic field, pitch angle distributions are mapped to the magnetospheric equator and sorted by equatorial crossing distance. The results are quantified using a standard function for the pitch angle distribution, f(a) = Asin K a (where a is the pitch angle and K is the power). Inside of ∼10 R S , the distributions are mostly peaked at 90°(K < 0), signifying a trapping distribution. Outside of this distance, the distributions are mostly field aligned (K > 0) with maxima near 0°and 180°. The 10 R S boundary maps to Saturn's ionosphere at latitudes equatorward of the aurora. Very few "flat" distributions are observed (K ≈ 0). The pitch angle distributions are not as well organized in local time as they are in radial distance, but over the 5 year survey between 10 and 20 R S field-aligned distributions appear most often near midnight, while trapping distributions are found elsewhere.

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Substorm associated magnetotail energetic electrons pitch angle evolutions and flow reversals: Cluster observation

Cited by 43 publications

References 29 publications

Kinetic structure and wave properties associated with sharp dipolarization front observed by Cluster

Kinetic structure and wave properties associated with sharp dipolarization front observed by Cluster

Case studies of mirror-mode structures observed by THEMIS in the near-Earth tail during substorms

Pitch angle distributions of energetic electrons at Saturn

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