LATE-PHASE ACCELERATION OF ENERGETIC IONS IN COROTATING INTERACTION REGIONS

We report on new high-sensitivity measurements from the WIND spacecraf t of the spatial distributions of 30 keV\amu to 10 MeV/amu ions from c orotating interaction regions (CIRs) that extend far beyond the confin es of the parent high-speed solar-wind stream. Not only do late-phase MeV ions persist far into the declining solar wind, but they also show a continual gain in energy, even after sector boundary passage, until the next small increase in solar wind speed occurs. These ions are ac celerated in the distant heliosphere as the reverse shock from the CIR propagates completely across the rarefaction region produced by the d eclining solar wind, growing in acceleration efficiency as it propagat es. Energetic ions from a single CIR event are seen for a period of 17 days and similar to 225 degrees in solar longitude. The observed ener gy spectra can be fit to the theory of Fisk and Lee [1980] only if sho ck compression increases with time so that the spectra harden signific antly.