Cosmic-ray diffusion in the inner heliosphere

• Published in: Advances in space research Vol. 35; no. 4; pp. 518 - 531
• Main Author: McKibben, R.B.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 2005
• Subjects: Interplanetary propagation; Jovian electrons; Solar energetic particles; Solar modulation; Ulysses mission; Jovian electrons; Ulysses mission; Interplanetary propagation; Solar modulation; Solar energetic particles
• ISSN: 0273-1177; 1879-1948
• DOI: 10.1016/j.asr.2005.01.022

For about the last 40 years, we have been trying to understand the propagation of cosmic rays and other energetic charged particles through the interplanetary medium. Identification of the basic processes affecting the propagation, namely diffusion, convection by the solar wind, adiabatic deceleration, and gradient and curvature drifts, was attained early on, but reaching detailed physical understanding, particularly of the roles of diffusion and gradient and curvature drifts, continues as an active topic of research to this day. Particularly unclear is the nature of the cross-field propagation. Many observations seem to require more efficient cross-field propagation than theoretical propagation models can easily produce. At the same time, there are other observations that seem to show strong guidance of the particles by the interplanetary magnetic field. With current measurements from spacecraft near Earth and from the Ulysses spacecraft, which samples nearly the complete range of heliographic latitudes in the inner heliosphere, critical tests of the ways in which cosmic rays and other energetic charged particles propagate through the interplanetary medium are possible. I briefly review the status of observations that are relevant to the characterization of diffusive propagation in the inner heliosphere and will present evidence for a possibly previously overlooked contribution from transport along magnetic flux tubes that deviate dramatically from the average interplanetary spiral configuration.