Stable ‘pancake’ distributions of low energy electrons in the plasma trough

Wrenn, G. L.; Johnson, J. F. E.; Sojka, J. J.

doi:10.1038/279512a0

Cited by 53 publications

(37 citation statements)

References 11 publications

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“…At 5 eV, the flux is more in equinox and winter months than in summer. This aspect conforms the observation of Wrenn et al [12], showing increase at 32 eV and decrease of suprathermal flux at 5 eV. Suprathermal electrons created in the ionosphere below 250 km lose their energy locally due to high-density neutral particles bringing the distribution function close to two component distribution.…”

Section: Resultssupporting

confidence: 92%

Observation of Suprathermal Flux from SROSS-C2 Data at Low Latitude

Pandey

Misra

2009

Research Letters in Physics

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The studies of suprathermal flux at equatorial latitude for low solar activity year of 1996 (from January to December) are reported. The retarding potential analyzer (RPA) data of Indian space research organization Stretched Rohini Satellite Series-C2 (SROSS-C2) are used. The suprathermal electron flux data are chosen in the height range of 475 ± 50 km. Seasional, latitudinal, and height variations of suprathermal flux having energy range above 30 eV along with comparisons in latitudinal variation of small energy superathermal flux of 5 eV are also reported. The data are selected during the period of local midnight to avoid contaminations from photoelectron flux and flux coming from coating of electrodes.

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Section: Resultssupporting

confidence: 92%

Observation of Suprathermal Flux from SROSS-C2 Data at Low Latitude

Pandey

Misra

2009

Research Letters in Physics

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“… Meredith et al [1999] have reported the observations of characteristic distributions in the restricted region at the equator outside the plasmapause, where the pitch angle distributions are formed with sharply peaked at 90° in the relatively low energy range below a few keV, which is known as a pancake distribution [ Wrenn et al , 1979]. Similar types of pitch angle distributions in keV combined with butterfly distributions were reported [ Åsnes et al , 2005].…”

Section: Introductionmentioning

confidence: 75%

“…The energetic electrons in the different energy ranges form pitch angle distributions especially peaked at 90°, which are called pancake distributions [ Wrenn et al , 1979; Meredith et al , 1999; Horne et al , 2003a]. The pancake distributions are formed below the energy of a few hundred keV.…”

Section: Pitch Angle Distributionmentioning

confidence: 99%

Coherent nonlinear scattering of energetic electrons in the process of whistler mode chorus generation

et al. 2009

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[1] Cyclotron resonant wave-particle interaction of whistler mode chorus emissions drives pitch angle scatterings of a wide range of energetic electrons in the magnetosphere. We study a coherent scattering process associated with generation of the whistler mode rising chorus emissions near the geomagnetic equator in a self-consistent electromagnetic fullparticle simulation. The simulation shows that coherent whistler mode rising chorus emissions scatter energetic electrons very effectively through formation of an electromagnetic electron hole. The nonlinear interaction induces acceleration of resonant electrons trapped by the wave and deceleration of untrapped resonant electrons. When the frequency of a rising chorus element continuously increases in time from lower frequencies to higher frequencies, the parallel resonant velocity continuously decreases toward lower-velocity ranges resulting in significant scattering of resonant electrons. The lower limit of resonant parallel velocity is determined by the upper frequency limit of the rising chorus element. The unscattered electrons with low parallel velocities and the accelerated resonant electrons trapped by the wave result in the distribution clearly peaked at 90°. Successive generation of rising chorus elements can scatter resonant electrons in the same resonance velocity range. The repeated scatterings make the distribution much sharper at 90°, leading to formation of a pancake distribution function as observed in the inner magnetosphere.

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“…Highly anisotropic electron velocity distributions, peaked at 90" to the magnetic field, were first detected by the suprathermal plasma analyzers on GEOS1 and GEOS2 [Wrenn et al, 1979]. These distributions were called pancakes from their appearance in velocity space and were characterized by a pancake index, defined as the flux ratio between 90 ø and 70 ø pitch angle.…”

Section: Introductionmentioning

confidence: 99%

“Pancake” electron distributions in the outer radiation belts

Meredith¹,

Johnstone²,

Szita³

et al. 1999

J. Geophys. Res.

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Abstract. Electron pitch angle distributions sharply peaked at 90 ø pitch angle were first recorded in the energy range 50 eV < E < 500 eV by the GEOS 1 and GEOS2 spacecraft in 1977/1978, from the plasmapause out to geostationary orbit. At the time they were explained as the remnants of pitch angle diffusion driven solely by electron cyclotron harmonic (ECH) waves. Here we report new observations by the Low Energy Plasma Analyser on board the Combined Release and Radiation Effects Satellite, which measured the complete pitch angle distribution over the energy range 100 eV < E < 30 keV. The pancake distributions are seen to develop from injected distributions that are nearly isotropic in velocity space, on a timescale that is greater than 2 hours. The freshly injected distributions are associated with strong ECH and whistler mode waves suggesting that the pancake distributions are likely to be caused by a combination of both wave types. Outside L = 6.0 the fitting analysis at energies in the range 100 eV < E < 1 keV shows that in the marginally stable state the phase space density contours lie approximately along the characteristic curves for diffusion by whistler mode waves determined independently from the plasma wave data. However, inside L = 6.0, significant departures are observed. Our results suggest that whistler mode waves play a dominant role in the formation of pancake distributions outside L = 6.0, whereas inside L = 6.0 and, in particular, in the vicinity of the plasmapause, the ECH waves also play a significant role. Consequently, both types of waves should be considered in any attempt to explain the diffuse aurora and the variation with L taken into account.

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Stable ‘pancake’ distributions of low energy electrons in the plasma trough

Cited by 53 publications

References 11 publications

Observation of Suprathermal Flux from SROSS-C2 Data at Low Latitude

Observation of Suprathermal Flux from SROSS-C2 Data at Low Latitude

Coherent nonlinear scattering of energetic electrons in the process of whistler mode chorus generation

“Pancake” electron distributions in the outer radiation belts

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