Compressive-Diffusive Acceleration of Energetic Charged Particles

Abstract

We discuss the phenomenon of the acceleration of charged particles in a compressing di~@usive medium and apply it to recent ACE observations in the interplanetary medium. It has been recognized that the phenomenon of di~@usive shock acceleration can readily be generalized to the case where the the shock isreplaced by a gradual change in the velocity of the ~Bow over a length scale LL . Let U be the ~Bow speed and κ the energetic particle di~@usion coe~Ccientt normal to the plane of the compression. Then, if the dimensionless parameter κ/(UL) is large compared with unity, the energetic particles are accelerated much as indi~@usive shock acceleration. We have applied this to the case of a co-rotatinn g interaction region near the Sun, where it has not yet developed into a shock. We ~And signi~Acant acceleration of charged particles. Our results are compaa red with recent observations carried out on the ACE spacecraft.