Evolution of the galactic cosmic ray electron to proton ratio: Ulysses COSPIN/KET observations

Abstract

The Ulysses orbit provides a unique opportunity to study the propagation of cosmic rays in a wide range of heliographic latitudes and during different solar activity and polarity in the inner heliosphere. Around July 2000 the solar magnetic field reversed its global polarity. In late 2000, the electron to proton ratio at the rigidities of 1.2 GV and 2.5 GV, measured by the Kiel Electron Telescope aboard Ulysses, was roughly the same as in the previous solar maximum. During 2001 the ratio profile began to flatten, however after late 2001 the ratio began to increase again, leading to the conclusion that drifts are becoming increasingly important again. Comparing the Ulysses observations with the IMP and ICE measurements in the 1980s reveals a similar time profile. If solar cycle 23 would evolve similar to solar cycle 21 then the electron intensity will increase more quickly than the helium and proton intensities in 2003/2004.