Irregular Magnetic Fields and Energetic Particles near the Termination Shock

The physics of magnetic field‐line meandering and the associated energetic‐particle transport in the outer heliosphere is discussed. We assume that the heliospheric magnetic field, which is frozen into the solar‐wind plasma, is composed of both an average and random component. The power in the random component is dominated by spatial scales that are very large (by a few orders of magnitude) compared to the shock thickness. The results from recent numerical simulations are presented. They reveal a number of characteristics which may be related to recent Voyager 1 observations of energetic particles and fields. For instance, low‐energy (tens of keV) particles are seen well upstream of the shock that also have large pitch‐angle anisotropies. Furthermore, low‐energy particles are readily accelerated by the shock, even though their mean‐free paths are very large compared to their gyroradii. When averaging over the entire system, the downstream spectra are qualitatively consistent with the theory of diffusive shock acceleration.