The effect of adiabatic deceleration on the cosmic ray spectrum in the solar system

Abstract

Cosmic rays in the magnetic fields carried in the solar wind are continually expanded and decelerated, in addition to being convected out of the solar system. The effect of the deceleration on the cosmic ray spectrum is calculated for the case that the outward convection of cosmic rays is small and for the case that the cosmic ray spectrum is a simple power law and the diffusion coefficient is independent of energy. The calculations are carried out for both particle momentum and energy. It is shown that a power law spectrum is preserved by the deceleration. It is shown that the deceleration contributes a decrease at high energies of about one third of the total modulation. Where the spectrum flattens out at lower energies, the deceleration produces an increase which partially cancels the reduction by convection.