Effects of particle drift on cosmic-ray transport. I - General properties, application to solar modulation

Abstract

Although gradient and curvature drifts are explicitly contained in the general equations of cosmic-ray transport, they have been almost universally neglected in applications of these equations. We evaluate the drifts explicitly for the Parker spiral magnetic field and show that, for particles with rigidities greater than approx.0.3 GV in the solar wind, they are larger than the solar-wind velocity over much of the heliosphere. Hence most current models of solar modulation and solar-flare particle events neglect terms which in many cases are as important as those retained. Calculations are presented which demonstrate the importance of the effects for simple modulation models. We conclude that comparisons of presently available model calculations with observations do not provide a fair test of transport theory since they neglect drifts. Drifts may substantially reduce the net modulation.