Reinterpretation of flux structures of solar protons and their use as probes of an open and closed magnetosphere

Abstract

In this article we question the capacity of higher energy solar protons to distinguish between open and closed magnetospheres, propose a new interpretation of flux structures detected at low altitudes, and develop a method that allows to infer from the structures observed the anisotropy of the flux in the interplanetary medium. This research is based on and extensive study of particle motion in closed and open magnetospheres, using the method of trajectory simulation with the help of mathematical models. Applied to the solar cosmic ray flux detected by Esro II during the February 28, 1969, event, the simulation showed that tens to hundreds of MeV protons cannot distinguish between an open and a closed field topology. From the flux structures observed at low altitude and the computed viewing angles of the satellite‐borne detectors, the anisotropic distribution function of cosmic ray flux in the interplanetary medium is derived; it presents a bidirectional anisotropy, from solar and antisolar directions, that agrees with flux anisotropies observed in the interplanetary medium and clearly account for the structures observed.