Simulation of Solar Wind Turbulence near Corotating Interaction Regions: Superposed Epoch Analysis of Simulations and Observations

Abstract

The effect of the turbulence that is associated with solar wind corotating interaction regions (CIRs) on transport of galactic cosmic rays remains an outstanding problem in space science. Observations show that the intensities of the plasma and magnetic fluctuations are enhanced within a CIR. The velocity shear layer between the slow and fast wind embedded in a CIR is thought to be responsible for this enhancement in turbulent energy. We perform physics-based magnetohydrodynamic simulations of the plasma background and turbulent fluctuations in the solar wind dominated by CIRs for radial distances between 0.3 and 5 au. A simple but effective approach is used to incorporate the inner boundary conditions for the solar wind and magnetic field for the periods 2007–2008 and 2017–2018. Legendre coefficients at the source surface obtained from the Wilcox Solar Observatory library are utilized for dynamic reconstructions of the current sheet and the fast and slow streams at the inner boundary. The dynamic inner boundary enables our simulations to generate CIRs that are reasonably comparable with observations near Earth. While the magnetic field structure is reasonably well reproduced, the enhancements in the turbulent energy at the stream interfaces are smaller than observed. A superposed epoch analysis is performed over several CIRs from the simulation and compared to the superposed epoch analysis of the observed CIRs. The results for the turbulent energy and correlation length are used to estimate the diffusion tensor of galactic cosmic rays. The derived diffusion coefficients could be used for more realistic modeling of cosmic rays in a dynamically evolving inner heliosphere.

A Numerical Study of the Effects of a Corotating Interaction Region on Cosmic-Ray Transport. II. Features of Cosmic-Ray Composition and Rigidity

“…For recent advances in MHD modeling of these inner heliospheric structures, see also Shiota et al (2017) and Usmanov et al (2018). Developing dedicated MHD numerical models for studying CIR effects on GCR transport followed, e.g., by Guo & Florinski (2014), Wiengarten et al (2014), Kopp et al (2017), and Ghanbar & Florinski (2023).…”

“…As for the diffusion coefficients (DCs), we note that progress has been made for various diffusion theories, e.g., Zhao et al (2017Zhao et al ( , 2018, but concerning the complexity of turbulence models and the uncertainty of its intrinsic parameters, a pragmatic phenomenological approach is adopted. For an advanced approach of how to relate the DCs to turbulence quantities associated with CIRs, see, e.g., Ghanbar & Florinski (2023). Following our previous model of the DCs, the components K ∥ and K ⊥ in K s are given by the following Figure 1.…”

“…These uncertainties also pertain to what is to be used as solar modulation parameters and entities in numerical modulation models, and at which level of sophistication and difficulty this is possible to do. For recent advances in MHD modeling in this context and how it relates to GCR transport, see Ghanbar & Florinski (2023). The common purpose of all the numerical modeling studies is to contribute meaningfully to advancing our understanding of this interesting heliospheric phenomenon.…”

Numerical Modeling of Energetic Charged-particle Transport with SPECTRUM Software: General Approach and Artificial Effects due to Field Discretization

“…More recently, fully 3D systems have been proposed with enhanced sets of equations that account for the effect of turbulence embedded in the macroscopic variables (Usmanov et al 2011;van der Holst et al 2014), leading to a more complete description of the plasma. Including the evolution of turbulent quantities in the MHD system can also be useful for later computation of particle transport coefficients (Ghanbari & Florinski 2023).…”