Spatial variation of >106MeV proton fluxes observed during the Ulysses rapid latitude scan: Ulysses COSPIN/KET results

The basic physical processes that lead to the longterm modulation of cosmic rays in the heliosphere have been known for many years. However, our knowledge of the relative importance of the various processes is still incomplete. Observations of cosmic rays at high latitudes can be used to improve our understanding of modulation processes. In this paper we present measurements of galactic proton fluxes with energies above 106 MeV made by the Kiel Electron Telescope on board the Ulysses spacecraft during the fast scan from the South polar passage in September 1994 to the North pole in August 1995, under solar minimum conditions. Comparison of proton fluxes at high latitudes and in the ecliptic shows a 20% higher flux in polar regions. The flux increase is not symmetric with respect to the heliographic equator but rather with respect to a surface shifted by 7 degrees South. In such a coordinate system the latitudinal gradient in both hemispheres has a value of (0.33 +/- 0.02)%/deg.