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GEOPHYSICAL RESEARCH LETTERS, VOL. 22, NO. 23, PAGES 3365–3368, 1995

Differences Between the 0.35-1.0 MeV/nucleon H/He Ratio in Solar and Co-Rotating Events at High Heliolatitude

G. M. Simnett

Department of Physics and Space Research, University of Birmingham, B15 2TT, United Kingdom.


K. A. Sayle

Department of Physics and Space Research, University of Birmingham, B15 2TT, United Kingdom.


E. C. Roelof

Johns Hopkins University/Applied Physics Laboratory, Laurel, Maryland.


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.

Received 11 April 1995; accepted 21 August 1995.

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Citation: Simnett, G. M., K. A. Sayle, and E. C. Roelof (1995), Differences Between the 0.35-1.0 MeV/nucleon H/He Ratio in Solar and Co-Rotating Events at High Heliolatitude, Geophys. Res. Lett., 22(23), 3365–3368.