Latitudinal and radial variation of >2 GeV/n protons and alpha particles in the southern heliosphere at solar maximum: Ulysses cospinket and neutron monitor network observations

Abstract

Ulysses, launched in October 1990, began in its second out-of-ecliptic orbit in September 1997 and its second fast latitude scan in November 2000. In contrast to the first orbit with the Sun declining to low activity, we are now at solar maximum conditions. The Kiel Electron Telescope (KET) on-board Ulysses measures proton and alpha-particles in the energy range from 5 MeV/n to >2 GeV/n. To derive radial and latitudinal gradients, data from the Chicago instrument on board IMP-8 and the neutron monitor network have been used. To determine the time profile of >2 GeV/n proton and alpha-particles at Earth further data reduction,as described in our previous work, is necessary.The latitudinal gradient obtained during the time period from 1997 to 2001 revealed a big difference between those found during Ulysses' first latitude scan in 1994 and 1995 during solar minimum activity. An approximation by a steady-state cosmic ray spatial distribution is characterized by a small radial and large latitudinal gradients, was interchanged with a highly variable one with a large radial and a small consistent with zero latitudinal gradient.