Theory of Cosmic Ray Modulation

Stefan E. S. Ferreira

Unit for Space Physics, North-West University (Potchefstroom Campus), 2520 Potchefstroom, South Africa

Cosmic rays in our heliosphere are subjected to different modulation processes: diffusion, convection, energy changes, gradient, curvature and current sheet drifts. These particles also encounter the termination shock where they get re-accelerated via diffusive shock acceleration to reach substantial higher energies. Apart from diffusive shock acceleration, heating and stochastic acceleration in the inner heliosheath may also be of importance especially for the anomalous component. An overview of the different modulation processes is presented and it is illustrated what can be learned from cosmic ray measurements in the heliosphere and from computations with various modulation models about important issues like e.g., the location and modulation effects of the termination shock, modulation and acceleration in the inner heliosheath, the size and shape of the heliosphere, the local interstellar spectra at lower energies, and the transport parameters and mechanisms.