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Electron distribution function formation in regions of diffuse aurora

The precipitation of high-energy magnetospheric electrons (E \~ 600 eV\textendash10 KeV) in the diffuse aurora contributes significant energy flux into the Earth\textquoterights ionosphere. To fully understand the formation of this flux at the upper ionospheric boundary, \~700\textendash800 km, it is important to consider the coupled ionosphere-magnetosphere system. In the diffuse aurora, precipitating electrons initially injected from the plasma sheet via wave-particle interaction processes degrade in the atmosphere toward lower energies and produce secondary electrons via impact ionization of the neutral atmosphere. These precipitating electrons can be additionally reflected upward from the two conjugate ionospheres, leading to a series of multiple reflections through the magnetosphere. These reflections greatly influence the initially precipitating flux at the upper ionospheric boundary (700\textendash800 km) and the resultant population of secondary electrons and electrons cascading toward lower energies. In this paper, we present the solution of the Boltzman-Landau kinetic equation that uniformly describes the entire electron distribution function in the diffuse aurora, including the affiliated production of secondary electrons (E < 600 eV) and its energy interplay in the magnetosphere and two conjugated ionospheres. This solution takes into account, for the first time, the formation of the electron distribution function in the diffuse auroral region, beginning with the primary injection of plasma sheet electrons via both electrostatic electron cyclotron harmonic waves and whistler mode chorus waves to the loss cone, and including their subsequent multiple atmospheric reflections in the two magnetically conjugated ionospheres. It is demonstrated that magnetosphere-ionosphere coupling is key in forming the electron distribution function in the diffuse auroral region.

Khazanov, G.; Tripathi, A.; Sibeck, D.; Himwich, E.; Glocer, A.; Singhal, R.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 11/2015

YEAR: 2015     DOI: 10.1002/2015JA021728

diffuse aurora; electron distribution; Wave-particle interaction


Approximate analytical solutions for the trapped electron distribution due to quasi-linear diffusion by whistler-mode waves

The distribution of trapped energetic electrons inside the Earth\textquoterights radiation belts is the focus of intense studies aiming at better describing the evolution of the space environment in the presence of various disturbances induced by the solar wind or by an enhanced lightning activity. Such studies are usually performed by means of comparisons with full numerical simulations solving the Fokker-Planck quasi-linear diffusion equation for the particle distribution function. Here, we present for the first time approximate but realistic analytical solutions for the electron distribution, which are shown to be in good agreement with exact numerical solutions in situations where resonant scattering of energetic electrons by whistler-mode hiss, lightning-generated or chorus waves, is the dominant process. Quiet-time distributions are well-recovered, as well as the evolution of energized relativistic electron distributions during disturbed geomagnetic conditions. It is further shown that careful comparisons between the analytical solutions and measured distributions may allow to infer important bounce and drift averaged wave characteristics (such as wave amplitude). It could also help to improve the global understanding of underlying physical phenomena.

Mourenas, D.; Artemyev, A.; Agapitov, O.V.; Krasnoselskikh, V.; Li, W.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 11/2014

YEAR: 2014     DOI: 10.1002/2014JA020443

electron distribution; pitch-angle distribution; Radiation belt