Energetic particles during the first and third Ulysses southern high-latitude excursions: Probing global corotating interaction region structure beyond 5 AU

Details Energetic particles during the first and third Ulysses southern high-latitude excursions: Probing global corotating interaction region structure beyond 5 AU Energetic particles during the first and third Ulysses southern high-latitude excursions: Probing global corotating interaction region structure beyond 5 AU

Sep 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007jgra..11209107l&link_type=abstract

Journal of Geophysical Research, Volume 112, Issue A9, CiteID A09107

Physics

3

Interplanetary Physics: Energetic Particles (7514), Interplanetary Physics: Corotating Streams, Interplanetary Physics: Solar Cycle Variations (7536), Interplanetary Physics: Interplanetary Shocks

Scientific paper

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 $\gtrsim$ 30°S (versus Λ $\gtrsim$ 13°S in the first orbit). When Ulysses finally emerged into the fast ($\gtrsim$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.

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