Implications of Increased Perpendicular Diffusion on the Tilt Angle Depedence of Electron Modulation in the Heliosphere

Abstract

For numerical solutions of Parker's cosmic ray transport equation to be compatible with the small latitudinal gradients observed for protons by Ulysses, enhanced perpendicular diffusion seems needed in the polar regions of the heliosphere. The role of enhanced perpendicular diffusion was further investigated by examining electron modulation as a function of the "tilt angle" α of the wavy current sheet, using a comprehensive modulation model including convection, diffusion, gradient, curvature and neutral sheet drifts. We found that by increasing perpendicular diffusion in the polar direction, a general reduction occurs between the modulation differences caused by drifts effects for galactic cosmic ray electrons as a function of α for the A > 0 (e.g. ∼1990 to ∼2000) and A < 0 (e.g. ∼1980 to ∼1990) solar magnetic polarity cycles.