Idealized model for the radial gradient of modulated cosmic rays.
Development of a conceptually idealized model for interpreting existing and future measurements of the radial gradient of modulated cosmic rays in the limit that deceleration and convection effects become comparable. The proposed model assumes that the modulated spectrum consists of two idealized regions: at low energy, below some critical transition energy T sub c, a region where the shape of the spectrum is assumed to be determined wholly by a balance between convection and deceleration effects; and, at higher energies, above T sub c, a region where the magnitude and shape of the spectrum are taken to be those given by the usual convection-diffusion modulation. The application of this model, invoking some straightforward assumptions about the behavior of T sub c, suggests that the radial gradient in the regime where deceleration processes are dominant may be related to the spectral index of the unmodulated spectrum at the energy T sub c and to the absolute level of modulation. This is in contrast to the gradient at high energies, above T sub c, which is related only to local interplanetary characteristics through convection and diffusion.