ROCKET OBSERVATIONS OF ELECTRON PITCH-ANGLE DISTRIBUTIONS DURING AURORAL SUBSTORMS

Abstract

Electron angular distributions obtained from three rocket flights during auroral substorms are described. Pitch-angle distributions of the incident electrons vary from isotropic to strongly peaked at pitch angles near 90°. Isotropic distributions are sometimes maintained for times at least of the order of minutes with very little change in intensity. When an anisotropic distribution persists for some time, the particle intensity is usually observed to decay.Following an intensity increase the angular distribution generally becomes more isotropic. The degree of isotropy attained following an intensity increase does not appear to depend on the magnitude of the increase but rather on the degree of isotropy before the increase.The intensity of upward moving electrons (pitch angles 90–180°) can in most cases be accounted for by atmospheric scattering and mirroring in the undisturbed geomagnetic field. A few cases are observed in which the electron intensity in the pitch-angle range 90–180° is probably larger than can be accounted for by normal scattering and mirroring. The effect of an ionospheric current on the intensity of upward moving electrons is considered.