Equatorial Pitch Angle Distributions Research Articles

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.

Pitch angle distributions and mirror point densities in the outer radiation zone

A method is presented for the calculation of the equatorial pitch angle distribution (unidirectional intensity distribution) of trapped radiation from the count rate of an omnidirectional detector along a line of force. An expression is derived for the calculation of the mirror point density from the equatorial pitch angle distribution. The method is applied to data obtained from the Space Technology Laboratories scintillation counter and the University of Chicago proportional counter on the Explorer VI satellite. The results from the scintillation counter show a relative absence of electrons with pitch angles of 90° during quiet periods, a sharp increase in such particles shortly after a sudden commencement magnetic storm, and restoration of the prestorm distribution at a higher intensity level after the storm. The results from the proportional counter are qualitatively similar with the exception of the apparent deficiency of 90° pitch angles during quiet periods, which does not appear.