More than mass proportional heating of heavy ions by supercritical collisionless shocks in the solar corona

Abstract

We propose a new model for explaining the observations of more than mass proportional heating of heavy ions in the polar solar corona. We point out that a large number of small scale intermittent shock waves can be present in the solar corona. The energization mechanism is, essentially, the ion reflection off supercritical quasi-perpendicular collisionless shocks in the corona and the subsequent acceleration by the motional electric field $\mathbf{E}=-(1/c)\mathbf{V}\times \mathbf{B}$. The acceleration due to $\mathbf{E}$ is perpendicular to the magnetic field, in agreement with observations, and is more than mass proportional with respect to protons, because the heavy ion orbit is mostly upstream of the quasi-perpendicular shock foot. The observed temperature ratios between O${}^{5+}$ ions and protons in the polar corona, and between $\alpha$ particles and protons in the solar wind are easily recovered.

arXiv comment11 pages, 2 figures