Intensities of galactic cosmic ray nuclei from the ecliptic to the south solar polar regions near solar maximum: observations from the ULYSSES COSPIN high energy telescope

Abstract

Ulysses reached its maximum south heliographic latitude of 80.2° S in late November 2000, near the maximum in the solar activity cycle and is now embarked on a fast latitude scan that will bring it to a perihelion at 1.34 AU near the solar equator by mid-May 2001. Throughout the period of increasing solar activity since Ulysses left the ecliptic in 1998, the variations of modulation observed at Ulysses and at IMP-8 near Earth have been closely similar despite the significant radial and latitudinal separations between the spacecraft. Thus latitudinal and radial gradients have remained small during the approach to maximum solar activity. A surprise is that at some energies, especially for protons with energies ∼35-70 MeV, the latitudinal gradients appear to have reversed even before the reversal of the solar magnetic dipole was complete. For this paper observations are available from the fast latitude scan to latitudes as low as ∼37° S. Even at these low latitudes, the Ulysses/IMP flux ratios remain well below one. Observations through perihelion when Ulysses is in the ecliptic near 1.3 AU will be crucial to determining whether the apparent negative gradients are real or the result of instrumental effects.