Abstract. This article presents an integrated analytical model on the injection efficiencies of the different ion species of the Anomalous component of the Cosmic Rays (ACRs) at the solar wind termination shock. We find that the injection into diffusive (first-order Fermi) acceleration is dominated by parallel ion diffusion and not by perpendicular diffusion unless the angle Ψ between the shock normal and the heliospheric magnetic field is almost exactly 90 • (89.3 • < Ψ ≈ 90 • ). In steady state the threshold speed for injection into first-order Fermi acceleration at a not exactly perpendicular solar wind termination shock -with the Parker shock angle Ψ ≈ 89.3 • -adjusts itself self-consistently. Increased anisotropic ACR flux amplifies Alfvénic turbulence which in turn suppresses parallel diffusion. It therefore increases the injection threshold and decreases the ACR flux until equilibrium is reached. For this equilibrium situation, we estimate the injection efficiencies of different species of suprathermal ions at the termination shock. We consider the following pre-acceleration processes: 1) momentum diffusion in compressional (ion-acoustic and magnetosonic) turbulence in the upstream supersonic solar wind and adiabatic cooling during convection to the termination shock; 2) reflection, transmission, and acceleration in the electric potential of the termination shock; and 3) momentum diffusion (stochastic or second-order Fermi acceleration) in the subsonic solar wind downstream of the termination shock in the inner heliosheath region. Our model results are compared to data from instruments on board the SOHO, ACE, Ulysses, and Voyager spacecraft.
We analyze suprathermal ions and plasma wave spectra upstream of interplanetary shocks driven by coronal mass ejection events. In particular, we analyze the competition between two processes: (1) the upstream wave generation by suprathermal protons accelerated at the shock, and (2) the cascading of wave energy in the inertial range of solar wind turbulence. We derive the cascading timescale from the comparison of particle and turbulent wave spectra with theory and conclude that amplified solar wind turbulence upstream of interplanetary traveling shocks is better described by Iroshnikov-Kraichnan-type rather than Kolmogorov-type wave diffusion.
The observations on magnetic field fluctuations and suprathermal ion spectra near the shocks driven by the coronal mass ejections during the time periods of the Bastille Day 2000 event and the Halloween 2003 events are summarized.
In the years 2004 and 2007, the instruments onboard the Voyager 1 and 2 spacecraft delivered unprecedented data on the structure of the solar wind termination shock. This shock has been assumed to be responsible for the acceleration of the anomalous component of cosmic rays from a pickup ion seed population derived from the interstellar neutral gas penetrating the heliosphere. In expectation of the Voyager observations near the termination shock and in the heliosheath region, detailed models have been developed on the acceleration mechanism for the anomalous cosmic rays and on the structure of the termination shock. Here, an overview on the models on injection mechanisms into first-order Fermi acceleration, stochastic acceleration in the supersonic and subsonic solar wind, shock mediation by suprathermal ions, and on shock reformation by ions reflected at the shock is given. Comparing the results of these models to the Voyager observations, we try to synthesize an updated picture on the acceleration process of the anomalous cosmic rays.
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