Charge sign dependence of cosmic ray modulation near a rigidity of 1 GV

Abstract

New observations of electron fluxes made in 1997 and 1998 extend our ongoing investigation of the relative modulation of positively and negatively charged particles. We compare electron fluxes measured on high‐altitude balloon flights with continuing observations of helium fluxes from the IMP 8 spacecraft and present new measurements of the primary cosmic ray positron abundance in 1997 and 1998. Electron fluxes during the 1984–1990 period show a flat topped distribution, whereas the positively charged He fluxes show a peaked distribution, with the peak in 1987. This is expected from modulation theory, including the role of drifts when the northern heliospheric magnetic field is inward, and the southern heliospheric field is outward. From 1990 to 1999, data are consistent with an inverse relationship, but electron data are too sparse to allow a definitive statement. Near a rigidity of 1 GV the relative abundance of electrons and helium nuclei is a weak function of the tilt angle of the heliospheric current sheet.