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A Langevin equation for charged particles in a plasma with electrostatic turbulence is developed from first principles in consistency with kinetic theory. For the case of ion-acoustic turbulence observed in the solar wind detailed results are given for a Gaussian-distributed stochastic force, which has to be expressed by the diagonalized velocity diffusion tensor.

Long radio-wave absorption observations have been used to investigate the D-region post-storm effect (PSE) and to develop a morphological scheme of a PSE. This scheme has been checked, using Explorer 45 equatorial electron pitch-angle distributions to determine electron life-times and pitch-angle diffusion coefficients during the magnetic storms of June and August, 1972. Time, energy, and L- dependences of the pitch-angle diffusion coefficient have been discussed.

Pitch-angle distributions of Electrons from 35 to 560 keV measured in the equatorial plane by Explorer 45 have been used to investigate the dynamic development of the electron population in the region L = 2.0 to 5.5. It is shown that energetic electron precipitation in middle latitudes, during the post storm effect in D-region absorption, depends on the pitch-angle diffusion of electrons in the slot-region as the plasmasphere density changes during the recovery phase.