Bidirectional about 1 MeV/amu ion intervals in 1973-1991 observed by the Goddard Space Flight Center instruments on IMP 8 and ISEE 3/ICE

Bidirectional energetic ion flows (BIFs) in the solar wind at 1AU during 1973-1991 are examined on the basis of about 1 MeV/amu data from the Goddard Space Flight Center instruments on ISEE3/ICE and IMP 8. BIFs are observed more frequently around solar maximum, when they are observed about 12 percent of the time compared with about 5 percent at solar minimum. Intervals with durations greater than 4 hr are observed on average approximately every 3-4 d at solar maximum and every 2 wk at solar minimum, with about 33 percent of these intervals following within 2 d of an interplanetary shock. Various coronal mass ejection signatures and BIFs greater than 1 MeV/amu usually do not coincide exactly, and additional bidirectional ion events are identified.