Time profile of solar energetic particles fit using a mean free path considering the radial dependence of both magnetic field strength and fluctuations

The radially dependent mean free path of solar energetic particles was calculated by considering the radially dependent magnetic field fluctuation, its correlation length and the variation of magnetic field strength along an Archimedean interplanetary magnetic field. A longer mean free path can be deduced as radial distance approaches the sun. That is, the mean free path at 0.1 AU is increased by 10 times for some typical values of radial dependence of magnetic field fluctuation (e.g., power index of radial dependence = −2), compared to the value at 1 AU. The focused pitch angle transport equation without adiabatic deceleration was solved for the obtained mean free path. The calculated time profiles are compared with observations of solar energetic particles. In some cases, very good matches to observed data for longer periods are obtained with shorter mean free paths than the original authors mentioned.