Longitude dependence of geomagnetically trapped electrons

A general Fokker‐Planck equation is deduced, which describes the distribution of geomagnetically trapped electrons as a function of longitude, time, energy, and mirror point field intensity. A special variable for the longitudinal position of a particle is introduced. The coefficients representing longitudinal drift, ionization loss, and multiple Coulomb scattering are derived. The physical interpretation of this equation is analyzed for several special cases. The equation is integrated numerically for a stationary case, for low L shells. The eigen‐mode electron distribution function for the longitude‐dependent problem is determined, and electron fluxes, energy spectra, B dependence, and mirror point trajectories are calculated for the area of the South American anomaly. The variation of these characteristics with local time in the anomaly is discussed. In general, results are in agreement with satellite observations. Coulomb scattering is certainly the most important pitch‐angle diffusion mechanism for low L shells and can reasonably account for the observed longitude dependence of electron fluxes on B‐L rings of h min ≳ 0 km. It cannot, however, explain the observed replenishment at higher B values ( h min < 0 km). Presently available experimental material is not complete enough to allow more quantitative conclusions about the extra scattering mechanism.