Energetic plasma sheet electrons and their relationship with the solar wind: A Cluster and Geotail study

Roziers, E. Burin des; Li, X.; Baker, D. N.; Fritz, T. A.; Friedel, R. H.; Onsager, T. G.; Dandouras, I.

doi:10.1029/2008ja013696

Cited by 20 publications

(35 citation statements)

References 69 publications

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“…Average γ in the plasma sheet obtained by Burin des Roziers et al [2009] is 4.04, while in our study the average γ is 3.3. Average γ in the plasma sheet obtained by Burin des Roziers et al [2009] is 4.04, while in our study the average γ is 3.3.…”

Section: Positive Correlation Between Power Law Index and Eer/eefcontrasting

confidence: 49%

Statistics of energetic electrons in the magnetotail reconnection

Zhou

Deng

et al. 2016

JGR Space Physics

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Magnetic reconnection has long been regarded as an important site for producing energetic electrons in solar terrestrial and astrophysical plasmas. The motivation of this paper is to provide the average properties of energetic electrons in reconnection region, which are crucial for understanding electron energization mechanism but are rarely known. We statistically analyzed the energetic electrons through 21 magnetotail reconnection events observed by Cluster spacecraft during the years of 2001–2005. Approximately 1200 data points with time resolution of 8 s have been collected for each spacecraft. Two parameters are examined: energetic electron rate (EER) and power law index. EER, which is defined as the ratio of the integrated energetic electron flux to the lower energy electron flux, is used to quantify the electron acceleration efficiency. We find that EER and energetic electron flux (EEF) are positively correlated with the power law index, i.e., the higher rate and flux generally corresponds to softer spectrum. This unexpected correlation is probably caused by some nonadiabatic heating/acceleration mechanisms that tend to soft the spectrum with high temperature. EER is much larger within the earthward flow than the tailward flow. It is positively correlated with the outflow speed Vx, while the correlation between EER and Bz is less clear. With the increment of earthward outflow speed, the occurrence rate of high EER also monotonically increases. We find that EER generally does not increase with the increment of perpendicular electric field |E⊥|, suggesting that adiabatic betatron and Fermi acceleration probably play minor roles in electron energization during magnetotail reconnection.

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Section: Positive Correlation Between Power Law Index and Eer/eefcontrasting

confidence: 49%

Statistics of energetic electrons in the magnetotail reconnection

Zhou

Deng

et al. 2016

JGR Space Physics

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“…Numerous studies addressed the magnetospheric plasma transport and sources [ Terasawa et al , ; Borovsky et al , , ; Wing and Newell , ]. There have been several statistical models for plasma sheet electrons derived from Geotail and Cluster data, such as, for example, Åsnes et al [] and Burin des Roziers et al []. Artemyev et al [] analyzed the electron temperature radial distribution in the magnetotail using THEMIS observations at r > 10 R E .…”

Section: Introductionmentioning

confidence: 99%

Solar wind‐driven variations of electron plasma sheet densities and temperatures beyond geostationary orbit during storm times

et al. 2016

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The empirical models of the plasma sheet electron temperature and density on the nightside at distances between 6 and 11 RE are constructed based on Time History of Events and Macroscale Interactions During Substorms (THEMIS) particle measurements. The data set comprises ∼400 h of observations in the plasma sheet during geomagnetic storm periods. The equatorial distribution of the electron density reveals a strong earthward gradient and a moderate variation with magnetic local time symmetric with respect to the midnight meridian. The electron density dependence on the external driving is parameterized by the solar wind proton density averaged over 4 h and the southward component of interplanetary magnetic field (IMF BS) averaged over 6 h. The interval of the IMF integration is much longer than a typical substorm growth phase, and it rather corresponds to the geomagnetic storm main phase duration. The solar wind proton density is the main controlling parameter, but the IMF BS becomes of almost the same importance in the near‐Earth region. The root‐mean‐square deviation between the observed and predicted plasma sheet density values is 0.23 cm−3, and the correlation coefficient is 0.82. The equatorial distribution of the electron temperature has a maximum in the postmidnight to morning MLT sector, and it is highly asymmetric with respect to the local midnight. The electron temperature model is parameterized by solar wind velocity (averaged over 4 h), IMF BS (averaged over 45 min), and IMF BN (northward component of IMF, averaged over 2 h). The solar wind velocity is a major controlling parameter, and IMF BS and BN are comparable in importance. In contrast to the density model, the electron temperature shows higher correlation with the IMF BS averaged over ∼45 min (substorm growth phase time scale). The effect of BN manifests mostly in the outer part of the modeled region (r > 8RE). The influence of the IMF BS is maximal in the midnight to postmidnight MLT sector. The correlation coefficient between the observed and predicted plasma sheet electron temperature values is 0.76, and the root‐mean‐square deviation is 2.6 keV. Both models reveal better performance in the dawn MLT sector.

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“…For μ calculation, we assume an isotropic electron distribution since electron pitch angle is not resolved in the data. This assumption has been widely used in research on magnetospheric dynamics [e.g., Hilmer et al , 2000; Taylor et al , 2004; Burin des Roziers et al , 2009], and is also supported by various works in the magnetosheath [e.g., Lavraud et al , 2009; Lu et al , 2011]. For the energetic electron flux, j , the Geotail/EPIC have two integral fluxes, >38 keV and >110 keV, while differential flux is required to calculate PSD.…”

Section: Flux and Phase Space Density (Psd) Comparisonmentioning

confidence: 94%

“…For the energetic electron flux, j , the Geotail/EPIC have two integral fluxes, >38 keV and >110 keV, while differential flux is required to calculate PSD. The differential flux is estimated by assuming the energy spectra of electrons varies as a power law j = AE − λ [ Burin des Roziers et al , 2009; Luo et al , 2011]. The A and λ can be determined using the following formula:

j_{> 38} = \int_{38}^{\infty} A E^{- λ} d E, j_{> 110} = \int_{110}^{\infty} A E^{- λ} d E

which leads to

λ = 1 - \frac{{log}_{10} \frac{j_{> 38}}{j_{> 110}}}{{log}_{10} \frac{38}{110}}, A = j_{> 38} \times \frac{(λ - 1)}{38^{1 - λ}}

where j >38 and j >110 are measured >38 keV and >110 keV integral fluxes, A is a constant, and λ is the instantaneous power law index for each time step.…”

Section: Flux and Phase Space Density (Psd) Comparisonmentioning

confidence: 99%

“…Could these heated electrons be further transported through radial diffusion into the outer magnetosphere near the magnetopause and finally supply the seed electrons for inner magnetosphere? If the electrons in the magnetosheath are not the source of energetic electrons in the outer magnetosphere, then there should be other acceleration processes within the magnetosphere which, for some reasons, are well correlated with solar wind variations ( Burin des Roziers et al [2009] and Luo et al [2011] found that the energetic electron flux in the magnetosphere has great correlation with the upstream solar wind speed and southward magnetic field). In the present study, based on the electron measurements inside and outside the magnetopause when Geotail crossed the magnetopause, we make a direct comparison between the energetic electron flux and electron PSD in the magnetosheath and in the magnetosphere, in order to address the important question of whether the electrons in the magnetosheath could be a direct source sufficient for energetic electrons in the outer magnetosphere.…”

Section: Introductionmentioning

confidence: 99%

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Comparison of energetic electron flux and phase space density in the magnetosheath and in the magnetosphere

Li¹,

Tu²,

Gong³

et al. 2012

J. Geophys. Res.

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Whether energetic electrons (10s of keV) in the magnetosheath can be directly transported into the magnetosphere and further energized through radial diffusion is significant in understanding the physical mechanisms for producing the radiation belt electrons (>100s of keV) in the magnetosphere. In this study, we analyze more than two hundred magnetopause crossing events using the energetic electron and magnetic field measurements from Geotail and compare the flux and phase space density (PSD) of the energetic electrons on both sides of the magnetopause. It is found that for most of the events (>70%), the fluxes and PSDs of energetic electrons in the magnetosheath are less than those in the magnetosphere, suggesting that the energetic electrons in the magnetosheath cannot be a direct source sufficient for the energetic electrons inside the magnetosphere. In fact, our analysis suggests a possible leakage of the energetic electrons from inside to outside the magnetopause. By investigating the average energetic electron flux distribution in the magnetosheath, we find that the energetic electron fluxes are higher near the bow shock and the magnetopause than in between. The high energetic electron flux near the bow shock can be understood as due to energization of electrons when they go through the bow shock. The relatively low flux of the energetic electrons in between indicates that it is difficult for the energetic electrons to travel from the bow shock to the magnetopause and vice versa, possibly because the energetic electrons near the bow shock and the magnetopause are all on open magnetic field lines and these two relatively intense energetic electron populations in the magnetosheath rarely get mixed.

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Energetic plasma sheet electrons and their relationship with the solar wind: A Cluster and Geotail study

Cited by 20 publications

References 69 publications

Statistics of energetic electrons in the magnetotail reconnection

Statistics of energetic electrons in the magnetotail reconnection

Solar wind‐driven variations of electron plasma sheet densities and temperatures beyond geostationary orbit during storm times

Comparison of energetic electron flux and phase space density in the magnetosheath and in the magnetosphere

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