The heliocentric longitude intensity profile of 15-Mev protons from the February 5, 1955, solar flare

Abstract

Simultaneous observations of 15-Mev protons from the solar flare of February 5, 1965, on Mariner 4 and IMP 2 show that the particle intensity decays faster near earth than at Mariner. It is shown that, if the longitudinal intensity profile for energetic flare particles is represented by a Gaussian in heliocentric longitude, then corotation of such a distribution past the two separated points of observation will account for this behavior. Furthermore, these observations provide a measure of the longitudinal scale of the distribution. In particular it is shown that the ratio of intensity at IMP 2 to that at Mariner 4 will be described by RIM(t) = Ro exp(-t/τ R) where τR is related directly both to Ψ, the half-width at 1/e times maximum of the assumed Gaussian distribution, and to the longitudinal separation of the two points of observation. The observations are well described by such an exponential relationship for the first 32 hours after the flare and yield for the half-width Ψ = 15.3 ± 1.0° throughout this period. The quoted limits on Ψ correspond to a limit on κ⊥, the diffusion coefficient perpendicular to the average spiral field, of κ⊥ ≲ 1.2 × 1019 cm²/sec. On the other hand, the magnitude of Ψ early in the flare requires a diffusion coefficient of κ⊥ ≃ 1.4 × 1020 cm²/sec if this initial width is to be explained by invoking only anisotropic diffusion from the immediate locality of the flare on the sun. The implications of this discrepancy are discussed with respect to the predictions of anisotropic diffusion and the random walk of magnetic field lines.