Uneven illumination of the polar caps by solar protons: Comparison of different particle entry models

Abstract

Recent solar proton measurements over the polar caps have shown up some startling features during times of interplanetary particle anisotropies. Explanations of the observations have been based on diffusive entry into the magnetotail, direct entry by motion along trajectories without scattering, and models incorporating both entry mechanisms. The direct entry mode is based on the computation of particle orbits, of points of access, and asymptotic directions at the magnetopause and in the tail. Although different research groups have used trajectory calculations in order to explain observed polar cap structure, there is considerable disagreement on the computed trajectories and especially on the proposed access mechanisms of solar particles to these trajectories at the magnetopause. In this paper the different models are evaluated, and it is found that the nonadiabatic reconnection model is in good accord with the observations, whereas other models show serious inconsistencies.