A generalized two-component model of solar wind turbulence and ab initio diffusion mean free paths and drift lengthscales of cosmic rays

TL;DR

This paper develops a comprehensive 3D two-component solar wind turbulence model coupled with MHD equations, improving cosmic ray transport predictions by aligning better with spacecraft data.

Contribution

It introduces a fully 3D, self-consistent two-component turbulence model integrated with MHD, enhancing the accuracy of cosmic ray diffusion and drift calculations.

Findings

Improved agreement with spacecraft measurements.

Enhanced predictions of cosmic ray mean free paths.

Validated against previous models with numerical solutions.

Abstract

We extend a two-component model for the evolution of fluctuations in the solar wind plasma so that it is fully three-dimensional (3D) and also coupled self-consistently to the large-scale magnetohydrodynamic (MHD) equations describing the background solar wind. The two classes of fluctuations considered are a high-frequency parallel-propagating wave-like piece and a low-frequency quasi-two-dimensional component. For both components, the nonlinear dynamics is dominanted by quasi-perpendicular spectral cascades of energy. Driving of the fluctuations, by, for example, velocity shear and pickup ions, is included. Numerical solutions to the new model are obtained using the Cronos framework, and validated against previous simpler models. Comparing results from the new model with spacecraft measurements, we find improved agreement relative to earlier models that employ prescribed background solar wind fields. Finally, the new results for the wave-like and quasi-two-dimensional fluctuations are used to calculate ab initio diffusion mean free paths and drift lengthscales for the transport of cosmic rays in the turbulent solar wind.