Investigation of Galactic Cosmic Rays Modulation by the Corotating Interaction Regions

Abstract:

Corotating interaction regions (CIRs) are produced as a result of the interaction between fast and slow
solar-wind streams, and quite ubiquitous in every region of the heliosphere. Observations shown that
the stream interfaces of CIRs between fast and slow solar wind streams and the leading edges of CIRs
are responsible for the depressions of galactic cosmic rays (GCRs) intensity. Based on the well known
local-scale expansion of the ideal MHD conservation law and the developed global MHD model of
CIRs in the heliosphere, we perform the numerical investigation of the transport and turbulence of the
solar wind fluctuation in CIRs. Turbulent energy density and correlation length distribution throughout
the heliosphere are presented, and further in turn used to compute the mean free path and perpendicular
diffusion coefficient of energetic particles. We attempt to use the plasma background from the global
MHD simulations and the transport coefficients in our existing stochastic cosmic-ray transport code to
numerically solve the Parker transport equation for GCRs. The modulated GCR spectrum from Voyager
2 observations near the termination shock was used at the external boundary condition. The computed
GCR spectral features and temporal profiles at any given location was directly compared with
observations by spacecraft based cosmic-ray detectors and neutron monitors on the ground, which will
greatly enhance our understanding of the physics of GCR modulation by the CIRs in heliosphere.