Acceleration in energetics ions (~1MeV) in corotating interaction regions

Abstract

We have correlated the ~1 MeV proton intensity (J) measured at corotating reverse shocks detected by Ulysses near the ecliptic plane and in the southern hemisphere with the shock strength and shock normal angle. We find that J is essentially independent of the shock strength below 29 degS, whereas between 29 deg and 41 degS J showed a good correlation with the same. The poor correlation below 29 degS is attributed to temporal variations in the background intensity and to the presence of particles accelerated at other corotating and transient shocks. J is also independent of the shock normal angle at all latitudes, which is probably due to the combined effects of the drift and diffusive acceleration processes. We compensate for the effects of variations in the background by assuming that two reverse shocks observed during the same ~26 day period accelerate particles out of the same background population. By correlating the ratio of the proton intensities with the ratios of the shock parameters for such pairs of reverse shocks, we show that the shock acceleration efficiency is well correlated with the strength but is independent of the normal angle.