Shock drift acceleration of pickup protons at corotating interaction regions

It has been demonstrated recently that the diffusive shock acceleration the ory based on the assumption that the velocity distribution function of part icles is close to isotropy is incapable of explaining observed spectra of i ons accelerated at shocks in corotating interaction regions. In the present paper the shock drift acceleration of protons suffering multiple reflectio ns at shock fronts is studied as applied to the forward and reverse shocks detected at Ulysses on day 20, 1993, and on day 22, 1993. The velocity dist ribution function is considered to be anisotropic near the shock fronts, an d the magnetic moment of particles is supposed to be an adiabatic invariant which is valid in the case of weak scattering.