Latitudinal and radial variation of >2 GeV n protons and α-particles in the northern heliosphere:: Ulysses COSPIN KET and neutron monitor network observations

Ulysses, launched in October 1990, crossed in December 1997 the heliographic equator and completed its first out of ecliptic orbits During the time period from February 1995 to November 1997 solar activity was low and the spacecraft scanned the latitude range from 80 degrees N to the heliographic equator. The Kiel Electron Telescope on-board Ulysses measures protons and alpha-particles in the energy range from 5 MeV/n to >2 GeV/n. To separate spatial and temporal variations of >2 GeV/n protons and alpha-particles along the spacecraft trajectory we used the data set from the world wide neutron monitor network. We found negligible latitudinal gradients below similar to 29 degrees N and for the radial gradient an upper limit of approximate to 0.5%/AU for > 2 GeV/n protons and a-particles. In the latitudinal range from similar to 25 to >70 degrees N the latitudinal gradient is similar to 0.17%/degrees and similar to 0.1%/degrees for >2 GeV/n protons and alpha-particles, respectively, independent of spacecraft latitude and radial distance. (C) 1999 COSPAR. Published by Elsevier Science Ltd.