Transport and acceleration of anomalous cosmic rays in the inner heliosheath

Abstract

[1] The transport and acceleration of anomalous cosmic rays in the inner heliosheath is studied. A unique two-dimensional hydrodynamic numerical model is used to calculate the interaction of the solar wind and the local interstellar medium, neutral hydrogen, and pickup ions. The divergence of the flow, heliospheric magnetic field, and Alfven speed are calculated and then inserted into model which calculates cosmic ray transport and acceleration in this heliosphere by solving the Parker particle transport equation. We show that adiabatic heating and stochastic acceleration plays a major role in explaining Voyager 1 observations both at the termination shock and in the inner heliosheath. While the inclusion of adiabatic heating in a numerical modulation model results in the correct spectral shape of accelerated anomalous particles for energies $10 MeV at the termination shock, stochastic acceleration effectively accelerates these particles further to anomalous energies out in the inner heliosheath. These accelerated particles are then modulated back inward, resulting in realistic radial gradients as well as an upturn in the anomalous cosmic ray spectra. A parameter study is also done to illustrate the sensitivity of these acceleration processes to different diffusion coefficients.

Modelling anomalous cosmic ray oxygen in the heliosheath

“…with κ P,0 ∈ [0, 1] a free parameter determining the effectiveness of this process (Kallenbach et al 2005;Zhang et al 2006;Moraal et al 2006;Ferreira et al 2007). In this study a value of κ P,0 = 0.5 is used throughout, unless otherwise stated.…”

“…This form of V r (r, θ) is based on the HD results of Ferreira et al (2007), where the steeper than r −2 decrease in the solar wind speed in this region (as is expected for a purely radial incompressible solar wind flow) is due to change exchange (Fahr et al 2000). Similar solar wind profiles were also observed in other HD models, e.g.…”

“…These include adiabatic heating occurring in the heliosheath Zhang et al 2006;Ferreira et al 2007), stochastic (Fermi II) acceleration (Kallenbach et al 2005;Zhang et al 2006;Moraal et al 2006;Ferreira et al 2007), regions of preferred acceleration at the flanks (e.g. McComas & Schwadron 2006) and in the equatorial nose region (e.g.…”

The heliospheric transport and modulation of multiple charged anomalous oxygen revisited

“…These include adiabatic heating Ferreira et al 2007), second order Fermi acceleration (e.g. Zhang 2006;Ferreira et al 2007), transient events (e.g. , preferred acceleration at the flanks (e.g.…”

“…This seemingly modulated portion of the ACR spectra has already been addressed previously by various authors, offering a wide range of explanations (and speculations). These include adiabatic heating Ferreira et al 2007), second order Fermi acceleration (e.g. Zhang 2006;Ferreira et al 2007), transient events (e.g.…”