Shock acceleration as source of the anomalous component of cosmic rays in the heliosphere

Abstract

Abstract provided by author:

Anomalous cosmic rays are low energy enhancements of the cosmic ray intensities that cannot be explained by standard modulation of galactic cosmic rays entering the heliosphere. Presently it is thought that these anomalous cosmic rays enter the heliosphere as interstellar neutrals that are singly ionized in the inner heliosphere, convected outward to the solar wind termination shock and accelerated there to cosmic ray energies. To study this problem a numerical solution scheme is developed to solve the Parker transport equation as function of time, magnetic rigidity and two spatial dimensions. A requirement of the numerical model is that it must be able to solve the Parker equation across the solar wind determination shock to describe particle acceleration in a self-consistent way. The basic solutions produced by this model are studied to compile a comprehensive set of solutions, including the modulation and re-acceleration of galactic cosmic rays, the acceleration of a low energy source of particles and the effects of curvature and gradient drifts on these solutions. The similarities between the acceleration and modulation of different species of particles in the heliosphere are studied. The quality and characteristics of the solutions produced by the numerical model are studied in detail to demarcate the useful solution ranges of the model. It is shown that the modulation state of singly charged Helium and Oxygen during the solar minima of 1977/78 and 1987 is well explained by this model. Similarly, the model is used to address the problem of anomalous Hydrogen as a combination of the re-acceleration of galactic protons and protons accelerated at the solar wind termination shock. This confirms our present undrestanding of the origin of these species quantitatively, while it also demonstrates the validity of the newly developed numerical model. Hysteresis or phase lag effects between the modulation of high and low energy particles are well-known. Following several previous calculations, we solve the transport equation to determine to what extent these lags are due to time-dependent effects in the modulation