Low frequency plasma turbulence and high energy particles at CIR-related shock waves

We present initial results from a survey of the low frequency magnetic field turbulence measured at the forward/reverse shock pairs associated with the interaction regions of high and low speed solar wind streams (CIRs). The magnetic field data are taken from vector helium and fluxgate magnetometer observations (VHM/FGM) aboard the Ulysses spacecraft between July 1992 and December 1993. A turbulence measure is defined as total wave power in the frequency range available from the raw data. This quantity is computed for the up- and downstream regions of the CIR-shocks and compared with the fluxes of 1 MeV protons and roughly 1 MeV/nucl. helium (Ulysses-EPAC measurements) at the time of shock crossing. We find a poor correlation between the upstream magnetic field turbulence and the high energy particle fluxes, and a high correlation between these quantities in the downstream region. The correlation between particle flux and field turbulence is best for the region roughly one gyroradius (of the high energy particles) downstream of the shock. Thus we conclude that wave-particle interactions in the downstream region, especially in the direct vicinity of the shock transition play an essential role for the acceleration of particles at CIR-related shock waves.