Radiation belt electron precipitation and its ionospheric effects at middle latitudes

The role of radiation belt electron precipitation into the Earth's atmosphere at middle geomagnetic latitudes is studied. First, the process of pitch angle scattering of energetic electrons in the radiation belts is modeled, and the flux angular distributions are obtained for all pitch angles, including the atmospheric bounce loss cone. This determines the angular distribution of the precipitating fluxes. Secondly, the interaction of these fluxes with the ambient atmospheric constituents is simulated, using the Fokker-Planck method; and the rate of energy deposition in the atmosphere is calculated at any given height. This gives rise to a significant rate of ion pair production in the lower ionosphere. Thirdly, the influence of this precipitation induced ionization on the structure and composition of the ionospheric D-region is modeled. Two specific classes of electron precipitation are studied; one is the quiet time ''drizzle'' occurring in the absence of geomagnetic disturbances; the second is the storm-time precipitation during the recovery phase of major geomagnetic storms with its substantial impact on the lower ionosphere. Computations are furthermore carried out for geomagnetically quiet times, and the results indicate that the electron precipitation can provide the dominant nocturnal ionization source for the D-region in a narrow belt of geomagnetic latitudes corresponding to the inner edge of the outer radiation zone (L approximately 4 to 5; Λ approximately 600 to 650) with ion pair production rates typically between 0.1 and 1 ion pair cm-3 sec-1 from about 60 to 90 kilometers at L = 5. (U.S.)