A two-dimensional, self-consistent model of galactic and anomalous cosmic rays in the solar wind

Abstract

We have developed a two-dimensional heliospheric model that includes galactic and anomalous cosmic rays as well as pickup ions. Cosmic rays are described via their number density in phase space, rather than pressure, as every preceding 2-D model has done. Cosmic-ray pressure is included in the total energy budget, allowing us to compute dynamical effects of the energetic particles on the solar wind. We include the magnetic field as well in order to consistently compute cosmic-ray diffusion coefficients. To accommodate' lower-energy cosmic rays with their short diffusion length, we implemented an adaptive mesh refinement code featuring improved spatial resolution near the termination shock. Our simulations show that galactic cosmic rays could substantially change the solar wind flow in the outer heliosphere. In particular, the solar wind is deflected towards the ecliptic plane during the positive solar cycle, resulting in faster wind near the current sheet. This is a result of large latitudinal gradients in the cosmic-ray pressure, caused by the difference in cosmic-ray drift patterns over latitude. We also found that anomalous cosmic rays have a minor effect on the solar wind. Their pressure is not sufficient to modify the termination shock significantly, a conclusion based on comparing model cosmic-ray spectra with observations. However, anomalous cosmic-ray acceleration occurs somewhat differently than thought before, and shock drift effects are not prominent. The spectra of these particles have an enhancement near the cutoff, that is not caused by shock drifts.