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GEOPHYSICAL RESEARCH LETTERS, VOL. 21, NO. 14, PAGES 1561–1564, 1994

Corotating Particle Enhancements Out of the Ecliptic Plane

G. M. Simnett


K. Sayle

Department of Physics and Space Research, University of Birmingham, B15 2TT, UK


E. C. Roelof

Johns Hopkins University/Applied Physics Laboratory, Laurel, MD 20723


S. J. Tappin

Department of Physics and Space Research, University of Birmingham, B15 2TT, UK


Abstract

We have studied > 40 keV ion and electron enhancements seen at Ulysses from a series of corotating interaction regions (CIR), from mid-1992 until the end of 1993. The event intensity increased up to latitude 20°S; after that the ion flux maxima decreased by ∼23%/deg while the electron maxima decreased more erratically, and more slowly, during the last half of 1993. After April, 1993, the electron increases lagged the ions by up to four days. The electron energy spectrum hardened both towards the end of the events and as the latitude went above ∼35°. The electron/ion delays and the electron spectral hardening are related to the three-dimensional structure of the reverse shocks at high latitudes. The H/He ratio at ∼0.4-1.2 MeV/nucleon decreased towards the end of each event; the mean minimum value was 3.5±0.3, lower than observed in earlier studies of CIR-associated events near the ecliptic plane. The He increases have recurred with a period of 26.0 days. There have been two phase changes: +4.3 days (February 1993) and +2.4 days (August 1993), related to changes in the coronal structure of the source regions for the high speed solar wind streams.

Received 31 January 1994; accepted 11 April 1994.

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Citation: Simnett, G. M., K. Sayle, E. C. Roelof, and S. J. Tappin (1994), Corotating Particle Enhancements Out of the Ecliptic Plane, Geophys. Res. Lett., 21(14), 1561–1564.