Transition to solar minimum at high solar latitudes: Energetic particles from corotating interaction regions

Abstract

One of the key questions to be addressed during the solar maximum phase of the Ulysses mission has been the nature of the ubiquitous energetic particle populations observed at all helio-latitudes from equator to poles. During the current, post-maximum phase of its mission, Ulysses has encountered the return to more stable solar wind, high speed stream structure, leading to the formation of stream and/or corotating interaction regions, in addition to the coronal mass ejection associated transients. The analysis reported here presents the identification of the first CIR after the recent solar maximum recorded by Ulysses COSPIN/LET at high helio-latitudes based on energetic particle composition data recorded in the ∼5-30 MeV/n range. The recurrent compression region appears during 3-6 solar rotations in 2002 and is observed from ≈52°N to ≈37°N heliographic latitude at heliocentric distances from ≈3.1 AU to ≈3.8 AU.