Electron Pitch Angle Distributions Research Articles

The acceleration and precipitation of Van Allen outer zone energetic electrons

The first part of this paper presents the experimental results of a particle correlation experiment conducted between the magnetosphere and the auroral zone. The precipitation time profiles and increases of outer zone energetic electron fluxes are extremely well correlated. The enhancement of electron fluxes observed at synchronous altitudes is predominantly in the 50- to 150-kev energies. The increases are non-adiabatic, because they are not correlated with δB/δt. The variations observed in higher energy electron fluxes are generally correlated with variations in the local magnetic field and hence can be accounted for by adiabatic theories. Energy spectrums of the equatorial and auroral zone electrons are similar, with typical e folding energies of about 20 kev for both regions. Lifetimes of the non-adiabatic electrons are typically 10³ sec but may be as short as ∼200 sec. The equatorial electron pitch angle distribution is anisotropic and peaked toward 90°. The anisotropy in the pitch angle distribution changes with time and shows dependence on the electron flux. Finally, the energy spectrum in the equatorial plane is pitch angle dependent, with a steeper spectrum for smaller pitch angle particles. The second part of this paper presents theoretical interpretations of the experimental results, which can be consistently interpreted in terms of local acceleration by using the strong pitch angle diffusion model.

Relationship between the flux magnitude and pitch-angle distribution for post-substorm auroral electrons

Measurements of pitch-angle distributions of auroral electrons with energies ranging from a few hundred ev to 60 kev and greater are reported. Electrons with energies of 35 kev or less were always isotropic over the loss cone to within a factor of 2 regardless of flux magnitude, whereas electrons with energies of 60 kev and greater showed a strong functional dependence between the flux magnitude and degree of isotropy. The high-energy electron pitch-angle distribution was strongly anisotropic for flux levels in the trapping region of 104 electrons/cm² ster sec or less but was isotropic for flux levels of 2.5 × 104 electrons/cm² ster sec or greater. Implications of these data with regard to theories or models of particle precipitation or acceleration are considered.

The mutual effect of precipitated auroral electrons and the auroral electrojet

Auroral electrojet perturbation of geomagnetic field perturbing pitch angle distribution of precipitated electrons, developing computer program for model calculations

The growth of our knowledge of the Earth's outer radiation belt

The development of our knowledge of the outer Van Allen radiation zone is surveyed. In general, the approach within each topic is historical. The early discoveries of the gross features of the radiation belt, the difficulties encountered in determining the electron energy spectrum, and the misinterpretation of geomagnetic storm intensity changes due to inadequate knowledge of the electron spectrum are discussed. Also considered are the equatorial pitch angle distributions of electrons, the presence of protons in the outer zone, and the question of a ‘slot’ between the inner and outer zones. The calculations of the neutron albedo contribution of electrons to the outer zone are reviewed; the contribution appears to be inadequate, because the resulting energy spectrum is incorrect, the intensity inadequate, and the required lifetime too long. Observations of electron precipitation into the atmosphere are briefly reviewed, and several possibilities for the connection of such observations to the intensity and lifetimes of trapped electrons are listed.