Ulysses high-latitude observations of ions accelerated by co-rotating interaction regions

Abstract

We present observations of energetic ions (E∼1 MeV) from the Ulysses spacecraft during its first pass from the ecliptic plane to the southern high-latitude regions of the heliosphere. At latitudes less than ∼13°S Ulysses was completely immersed in the heliomagnetic streamer belt, and observed a ∼1 MeV proton intensity which showed little evidence of a periodic structure. Between ∼13°S and ∼29°S Ulysses observed one dominant recurrent co-rotating interaction region, its reverse shocks being mainly responsible for accelerating the ∼1 MeV protons. At ∼29°S the spacecraft left this region and entered the solar wind flow from the polar coronal hole. From ∼29° up to ∼45°S, reverse shocks from this and other interaction regions were still being observed. Accelerated energetic ions, with proton-to-alpha ratio signatures consistent with having been accelerated by the reverse shocks of these co-rotating interacting regions, were still being observed up to latitudes of ∼50°S.