Abstract
Energetic particles during the first and third Ulysses southern high-latitude excursions: Probing global corotating interaction region structure beyond 5 AU
Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
We analyze energetic particle observations during the first and third ascents of Ulysses to the southern regions of the heliosphere.
The first high-latitude excursion occurred in the declining phase of solar cycle 22, while the third occurred in a later phase
of solar cycle 23. In contrast to the long-lived and well-defined ∼26-day recurrent intensity enhancements observed throughout
the first southern excursion, observations during the third southern excursion showed a more variable structure. Transient
events of solar origin were more abundant and intense. Corotating interaction regions (CIRs) were clearly present in intermittent
sequences lasting only a few solar rotations. Within these sequences the relationships between solar wind structures and energetic
particle events were remarkably similar to those observed in the steady recurrences of the first southern excursion. Energetic
particles associated with well-formed CIRs bounded by strong forward and reverse shock pairs were not observed until heliographic
latitudes Λ
30°S (versus Λ
13°S in the first orbit). When Ulysses finally emerged into the fast (
700 km s−1) solar wind at Λ ≥ 39°S, particle events were variable and either associated with weak reverse shocks or without solar wind
signatures indicative of local CIRs (just as in solar cycle 22). The time-intensity profiles in individual CIRs matched up
well between the two southern excursions implying that essentially the same CIR structure existed in both solar cycles, albeit
at a higher latitude in solar cycle 23 and only in the midst of the intermittent recurrent sequences.
Received 22 March 2007; accepted 26 June 2007; published 22 September 2007.
Citation: (2007), Energetic particles during the first and third Ulysses southern high-latitude excursions: Probing global corotating interaction region structure beyond 5 AU, J. Geophys. Res., 112, A09107, doi:10.1029/2007JA012414.
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