Particle drift effects on cosmic ray modulation during solar maximum Original Research Article

A fully time-dependent cosmic ray modulation model based on the numerical solution of Parkerʹs transport equation is used to study the amount of particle drifts needed to explain the observed 1.2 GV electron to Helium ratio at Earth and the 2.5 GV electron to proton ratio (e/p) observed by the KET instrument on the Ulysses spacecraft. The model successfully simulates the modulation of protons, electrons and Helium ions for 11-year and 22-year cycles. It is based on the compound approach that incorporates the concept of propagation diffusion barriers combined with global increases in the HMF when propagated from the Sun throughout the hehosphere, as well as drifts and the other basic modulation mechanisms. It is found that less than 10% drifts is needed at solar maximum, when the solar magnetic field reverses, to explain the observed e/p along the Ulysses trajectory.