Differences between the 0.35-1.0 MeV/nucleon H/He ratio in solar and Co-rotating events at high heliolatitude

Abstract

We discuss measurements from the Ulysses spacecraft of the 0.35-1.0 MeV/nucleon H/He intensity ratio at high heliolatitudes. In early 1994 two transient solar events were detected in the gaps between particle intensity increases associated with the passage at low latitude of a co-rotating interaction region. The H/He ratio was ≳ one order-of-magnitude lower in the co-rotating events than in the transient solar events. Several similar instances, but not so cleanly separated, were observed from mid-1992 to the end of 1993. We interpret the lower H/He ratio in recurrent events as the result of efficient acceleration of interstellar pickup He⁺ at corotating reverse shocks to which Ulysses remains connected even at high heliolatitudes.