The influence of the Earth's atmosphere on geomagnetically trapped particles

The motion of energetic, charged particles trapped in the geomagnetic field is reviewed, and the methods of calculating the effect of the ambient atmosphere on trapped electrons and protons are presented. The results of these theoretical considerations are compared with the available experimental data to determine the spatial regions where collisions of the trapped particles with atmospheric constituents govern the long‐term behavior of the particles. It is concluded that during periods of minimum solar activity atmospheric collisions are the most important loss mechanism for electrons in the region L ⪝ 1.25, where L is McIlwain's magnetic shell parameter. Above this region the behavior of electrons is controlled by other, at present unknown, forces. For protons, it appears that the atmosphere controls the loss rate for the spatial region L ⪝ 1.4, although the evidence for this conclusion must be considered tentative at present.