Galactic cosmic rays in the heliosphere

Abstract

Galactic cosmic rays entering the heliosphere are subjected to four modulation processes: diffusion, convection, adiabatic deceleration in the expanding solar wind, gradient, curvature and current sheet drifts. These particles also encounter the termination shock where they may get re-accelerated via diffusive shock acceleration to reach substantial higher energies. An overview of these processes is presented with emphasis on the outer heliosphere where a considerable amount of modulation may take place, especially in the region between the termination shock and the modulation boundary/heliopause. It is illustrated what can be learned from cosmic ray measurements in the outer heliosphere and from computations with various modulation models about important issues like e.g., the location and modulation effects of the termination shock, modulation in the heliosheath, the size and shape of the heliosphere, the local interstellar spectra at lower energies, and the transport parameters and mechanisms.