THE ULYSSES NORTH POLAR PASS - LATITUDINAL GRADIENTS OF ANOMALOUS COSMIC-RAY O, N AND NE

A key finding of the Ulysses mission has been the absence of large lat itudinal gradients in the Anomalous Cosmic Ray (ACR) component. Studie s using data from several satellites have consistently shown a small ( similar to 2%/deg.) positive latitudinal gradient for anomalous O, N a nd Ne in the energy range 4 to 30 MeV/n, and even smaller gradients fo r ACR He. In this paper we use data from the COSPIN/LET experiment on board Ulysses to investigate (a) the behaviour of the ACR latitudinal gradients during the passage over the northern polar regions, and (b) possible north-south asymmetries. The descent from the north pole has taken place under solar minimum conditions, providing a unique opportu nity to study fully developed latitudinal effects. Our data survey cov ers three ACR species, O (4 to 20 MeV/n), N (4 to 20 MeV/n) and Ne (4 to 30 MeV/n). ACR gradients have been calculated for three different r egions: 0 degrees-20 degrees (similar to 5%/deg.), 20 degrees-60 degre es (similar to 3%/deg.) and 60 degrees-80.2 degrees (similar to 1%/deg .). Comparison of data from the northern and southern hemishere at a g iven latitude shows an asymmetry with higher fluxes in the north than in the south at a given latitude.