The Relationship between Corotating Energetic Ion Enhancement and Solar Wind Speed at 1 AU

A series of corotating energetic helium events with 3-5 MeV/n has been observed by the HEP telescopes onboard the GEOTAIL satellite at 1 AU from October 1993 to August 1994. We have examined the relationship between solar wind (SW) speeds observed at 1 AU and the intensity of He in the series of the corotating interaction region (CIR) events. The speed difference of the high-speed SW from slow-speed SW, which forms a CIR in the outer heliosphere, shows a reasonable correlation with the peak intensity of He at 3-5 MeV/n. The speed difference of those SWs is considered to be related to the shock strength which develops in a CIR at a distance from the Sun. Such a correlation between energetic ions associated with CIRs and SW speed has not been shown so far for the events during the period of 1978-1986. We have also investigated the dependence of the relation between the CIR ion events and the SW speeds during the period between 1978 and 1995 which corresponds to the high solar active phase of Solar Cycle 22. There is a good correlation between the SW speed and the peak intensity of CIR energetic ions in the quiet phase of solar activity, but not in the active phase.