Heliospheric modulation of galactic electrons: Consequences of new calculations for the mean free path of electrons between 1 MeV and ∼10 GeV

Abstract

With several new incentives, revisiting electron modulation using a comprehensive numerical model is appropriate. First, one has better confidence in the galactic electron spectrum at energies ≤ 300 MeV, second, several good independent observations of modulated electron spectra at 1 AU at solar minimum and along the Ulysses trajectory have been made, and third, progress has been made about theoretical predictions for mean free paths in the heliosphere. In this work, as a first approach, an assessment of the various new predictions for electron parallel mean free paths at 1 AU, especially their rigidity dependencies, is made by looking at the effects of these predictions on heliospheric modulation of galactic electron at energies below ∼300 MeV. Electron modulation is most suitable at these energies because adiabatic energy changes are still negligible and drift effects become less important. Several spectra are shown together with the radial dependence in the equatorial plane of the electron fluxes associated with each approach that was used. It was found that a damping turbulence model with composite slab, two‐dimensional geometry gave parallel mean free paths that resulted in reasonable electron modulation at these energies. However, several other important modulating parameters have to be considered of which diffusion perpendicular to the averaged magnetic field is arguably the most important.