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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 72 (1995), S. 327-330 
    ISSN: 1572-9672
    Keywords: Heliosphere ; Energetic particles ; co-rotating interaction regions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The characteristics of the recurrent electron (38–53 keV) and ion (〉∼0.5 MeV) enhancements observed by Ulysses from mid-1992 to April 1994 are presented. The magnitude of the ion flux increases reached a maximum at a latitude of ∼20°S and decreased afterwards by ∼23%/degree until early 1994. The magnitude of the electron increases showed a similar trend until May, 1993, after which time it became approximately constant, until it started to increase again in early 1994. The electron enhancements have lagged the protons by up to 5 days once Ulysses left the heliospheric current sheet (mid-1993). The electron spectral index tended to harden (a) during the decay of the event and (b) as the latitude increased, up to 50°S. The events have recurred on a 26.0 day period, but with significant phase shifts over the 25 rotations studied. The H/He ratio decreases across the maximum intensity. The mean minimum value for H/He was 3.5±0.3, lower than that measured in previous studies in the ecliptic plane.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 72 (1995), S. 309-314 
    ISSN: 1572-9672
    Keywords: Heliosphere ; Energetic particles ; Corotating high-speed streams
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract As Ulysses moved inward and southward from mid-1992 to early 1994 we noticed the occasional occurrence of “inter-events”, lasting about 10 days and falling between the recurrent events, observed at proton energies of 0.48–97 MeV, associated with Corotating Interaction Regions (CIR). These inter-events were present for several sequences of two or more solar rotations at intensity levels around 1% of those of the neighbouring main events. When we compared the Ulysses events with those measured on IMP-8 at 1 AU we saw that the inter-events appeared at Ulysses after the extended emission (〉10 days) of large fluxes of solar protons of the same energy that lasted at least one solar rotation at 1 AU. The inter-events fell completely within the rarefaction regions (dv/dt〈0) of the recurrent solar wind streams. The interplanetary magnetic field (IMF) lines in the rarefactions map back to the narrow range of longitudes at the Sun which mark the eastern edge of the source region of the high speed stream. Thus the inter-events are propagating at mid-latitudes to Ulysses along field lines free from stream-stream interactions. They are seen in the 0.39–1.28 MeV/nucleon He, which exhibit a faster decay, but almost never in the 38–53 keV electrons. We show that the inter-events are unlikely to be accelerated by reverse shocks associated with the CIRs and that they are more likely to be accelerated by sequences of solar events and transported along the IMF in the rarefactions of the solar wind streams.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 72 (1995), S. 303-308 
    ISSN: 1572-9672
    Keywords: Heliosphere ; Energetic particles ; Shock acceleration ; Reverse shocks
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We examine the intensity, anisotropy and energy spectrum of 480–966 keV protons and 38–315 keV electrons observed by the HI-SCALE instrument on Ulysses associated with Corotating Interaction Regions (CIR) from mid-1992 to early 1994. The particle events are most clearly ordered by the reverse shocks bounding the CIRs. The bulk of the ion fluxes appear either straddling, or with their maximum intensity following, the reverse shock. The electron intensities rise sharply to their maximum upon the passage of the reverse shock, and are delayed with respect to the protons. We believe that following acceleration at the reverse shock the electrons re-enter the inner heliosphere and mirror, to return to the reverse shock for repeated acceleration. This process is more effective for electrons (v∼c/2) than for ions, and also favours the higher velocity electrons, which accounts for the observed spectral hardening with latitude.
    Type of Medium: Electronic Resource
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