A Simplified Ab Initio Cosmic-ray Modulation Model with Simulated Time Dependence and Predictive Capability

A simplified ab initio approach is followed to model cosmic-ray proton modulation, using a steady-state three-dimensional stochastic solver of the Parker transport equation that simulates some effects of time dependence. Standard diffusion coefficients based on Quasilinear Theory and Nonlinear Guidi...

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Bibliographic Details
Published in:The Astrophysical journal 2018-06, Vol.859 (2), p.107
Main Authors: Moloto, K. D., Engelbrecht, N. E., Burger, R. A.
Format: Article
Language:English
Subjects:
Astrophysics
Computer simulation
Cosmic ray intensities
Cosmic ray modulation
Cosmic ray protons
Cosmic rays
Diffusion
Magnetic fields
Mathematical models
Modulation
Solar magnetic field
Solar minimum
Solar wind
Solar wind velocity
Spacecraft
Sun: heliosphere
Three dimensional models
Time dependence
Transport equations
Turbulence
Wind speed
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Summary:A simplified ab initio approach is followed to model cosmic-ray proton modulation, using a steady-state three-dimensional stochastic solver of the Parker transport equation that simulates some effects of time dependence. Standard diffusion coefficients based on Quasilinear Theory and Nonlinear Guiding Center Theory are employed. The spatial and temporal dependences of the various turbulence quantities required as inputs for the diffusion, as well as the turbulence-reduced drift coefficients, follow from parametric fits to results from a turbulence transport model as well as from spacecraft observations of these turbulence quantities. Effective values are used for the solar wind speed, magnetic field magnitude, and tilt angle in the modulation model to simulate temporal effects due to changes in the large-scale heliospheric plasma. The unusually high cosmic-ray intensities observed during the 2009 solar minimum follow naturally from the current model for most of the energies considered. This demonstrates that changes in turbulence contribute significantly to the high intensities during that solar minimum. We also discuss and illustrate how this model can be used to predict future cosmic-ray intensities, and comment on the reliability of such predictions.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/aac174