Studies of Solar Protons with Explorers XII and XIV.

Abstract

Four solar proton events observed by Explorers XII and XIV in 1961 and 1962 are discussed These events are directly associated with solar activity and, in three cases, are followed either by secondary events delayed by about 2 days or by recurrent events on succeeding solar rotations It is shown that the rate of propagation of solar protons is, in some of the primary events, linearly dependent on particle velocity. For example, the time taken to reach maximum intensity is inversely proportional to velocity. It follows that the mode of propagation (as measured by the distance traveled in reaching the Earth, for example) is independent of velocity. This result makes possible a separation of source characteristics from propagation effects. In each event which shows a velocity dependence, the maximum intensity is reached long after the rectilinear travel time. We conclude from this that propagation involves an important degree of scattering and that the degree of scattering is independent of energy over the observed range of 1 4 to 500 MeV. The energy spectrum at the time of escape from the Sun, the "source spectrum," is determined in each event which shows a velocity dependence. In each case it is a power law in kinetic energy from a few MeV to several hundred MeV. All events show periodic fluctuations in intensity, which are simultaneous at all energies and have a period of from 1 to 1.5 hours depending on the event The lack of dispersion indicates the existence of a periodic structure either in the solar wind or in the region between the magnetosphere and the Earth's shock front.