An AB initio model for cosmic-ray modulation
Abstract
A proper understanding of the effects of turbulence on the diffusion and drift of cosmic rays (CRs) is of vital
importance for a better understanding of CR modulation in the heliosphere. This study presents an ab initio model
for CR modulation, incorporating for the first time the results yielded by a two-component turbulence transport
model. This model is solved for solar minimum heliospheric conditions, utilizing boundary values chosen so that
model results are in reasonable agreement with spacecraft observations of turbulence quantities in the solar ecliptic
plane and along the out-of-ecliptic trajectory of the Ulysses spacecraft. These results are employed as inputs for
modeled slab and two-dimensional (2D) turbulence energy spectra. The modeled 2D spectrum is chosen based
on physical considerations, with a drop-off at the very lowest wavenumbers. There currently exist no models or
observations for the wavenumber where this drop-off occurs, and it is considered to be the only free parameter in this
study. The modeled spectra are used as inputs for parallel mean free path expressions based on those derived from
quasi-linear theory and perpendicular mean free paths from extended nonlinear guiding center theory. Furthermore,
the effects of turbulence on CR drifts are modeled in a self-consistent way, also employing a recently developed
model for wavy current sheet drift. The resulting diffusion and drift coefficients are applied to the study of galactic
CR protons and antiprotons using a 3D, steady-state CR modulation code, and sample solutions in fair to good
agreement with multiple spacecraft observations are presented.
URI
http://hdl.handle.net/10394/13665https://doi.org/10.1088/0004-637X/772/1/46
http://iopscience.iop.org/0004-637X