The Acceleration of Charged Particles in Corotating Interaction Regions (Cir) – a Review with Particular Emphasis on the Ulysses Mission

Observations on the acceleration of charged particles to higher energies in corotating interaction regions in interplanetary space are reviewed. Particular emphasis is given to the Ulysses observations which at the moment provide the latest extensive set. By comparison with Pioneer 10/11, Voyager, ISEE 3, and IMP 8, data collected during solar minimum periods, the nature of these phenomena now become much clearer. The introduction describes the formation and peculiarities of corotating interaction regions starting with a brief description of the formation of shocks in the interplanetary medium. Section 2 gives a brief description of the Ulysses mission and its orbit and is followed in Section 3 by the observational material. It is organized such that after earlier observations are introduced upstream effects are described, then we mention the different shapes of energy spectra, and describe what is known on elementary composition. Particular emphasis is given to the observations of the proton to alpha particle ratio, which is related to the important question on the origin of the accelerated particles: Are there energetic seed particles of some 10 keV energy, or do the accelerated particles stem from the solar wind flow reservoir? Are there other sources? After the angular distribution of the accelerated population are described we turn to the question of the efficiency of acceleration by corotating shocks: Is the efficiency a function of certain shock parameters only? Is there a latitudinal dependence? Can the observations be understood by assuming a pure heliodistance dependence? We also discuss the acceleration of electrons in corotating shocks to quite high energies (which is not understood), and mention the effects of corotating structures on extremely high energetic particles like the cosmic rays or the anomalous component before closing this section with a summary of the observational facts. Section 4 briefly summarizes theoretical aspects of the acceleration of particles by CIR-shocks and finally we discuss the material with particular emphasis on three aspects: The latitudinal and/or heliodistance dependence of the phenomena, the elemental composition and the role of pick up ions in the Heliosphere, especially with respect to acceleration in corotating shocks.