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GEOPHYSICAL RESEARCH LETTERS, VOL. 22, NO. 23, PAGES 3361–3364, 1995

Heliolatitude Dependence of Interplanetary Heavy Ions

C. G. Maclennan

AT&T Bell Laboratories, Murray Hill, NJ

L. J. Lanzerotti

AT&T Bell Laboratories, Murray Hill, NJ

G. M. Simnett

School of Physics and Space Research, University of Birmingham, UK

K. A. Sayle

School of Physics and Space Research, University of Birmingham, UK

Abstract

In its rapid traversal of 80° of heliolatitude from the southern solar pole to the equator, the HI-SCALE instrument on the Ulysses spacecraft measured the composition of ions accelerated at the co-rotating interaction regions (CIRs) that it crossed. We compare ion composition measurements as a function of heliolatitude during this traversal to those made on the ascent to the southern solar pole. The C/O ratio (∼1) in the fast traverse at ∼1.4 AU is found to be about twice the value (∼0.5) found previously in the ecliptic as well as at intermediate latitudes beyond ∼2 AU. For the CIR-associated events in the southerly high speed solar wind stream, the ion intensity enhancements are found to decrease monotonically with increasing heliolatitude once Ulysses crossed ∼20°S. Thus, the optimum region for CIR-related particle acceleration in solar minimum conditions occurs near the boundary of the current sheet at distances between the orbits of Mars and Jupiter. These results, together with HI-SCALE results on the heliolatitude dependence of anomalous oxygen suggest that the lower value of the C/O ratio arises from the enhanced (relative to 1 AU) abundance of low energy anomalous O at heliolatitudes beyond the current sheet and distances beyond ∼2 AU.

Received 15 June 1995; accepted 28 August 1995.

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Citation: Maclennan, C. G., L. J. Lanzerotti, G. M. Simnett, and K. A. Sayle (1995), Heliolatitude Dependence of Interplanetary Heavy Ions, Geophys. Res. Lett., 22(23), 3361–3364.

Copyright 1995 by the American Geophysical Union.