IMPLEMENTING TURBULENCE TRANSPORT IN THE CRONOS FRAMEWORK AND APPLICATION TO THE PROPAGATION OF CMEs

Abstract

We present the implementation of turbulence transport equations in addition to the Reynolds-averaged MHD equations within the Cronos framework. The model is validated by comparisons with earlier findings before it is extended to be applicable to regions in the solar wind that are not highly super-Alfvénic. We find that the respective additional terms result in absolute normalized cross-helicity to decline more slowly, while a proper implementation of the mixing terms can even lead to increased cross-helicities in the inner heliosphere.The model extension allows to place the inner boundary of the simulations closer to the Sun, where we choose its location at 0.1 AU for future application to the Wang-Sheeley-Arge model. Here, we concentrate on effects on the turbulence evolution for transient events by injecting a coronal mass ejection (CME). We find that the steep gradients and shocks associated with these structures result in enhanced turbulence levels and reduced cross-helicity. Our results can now be used straightforwardly for studying the transport of charged energetic particles, where the elements of the diffusion tensor can now benefit from the selfconsistently computed solar wind turbulence. Furthermore, we find that there is no strong back-reaction of the turbulence on the large-scale flow so that CME studies concentrating on the latter need not be extended to include turbulence transport effects.

A Generalized Two-Component Model of Solar Wind Turbulence and Ab Initio Diffusion Mean-Free Paths and Drift Lengthscales of Cosmic Rays

“…The regions with stronger generation of turbulence are associated with cross helicities quickly going to zero in their respective component. In other regions, cross helicities that are notequal tozero are retained also at large radial distances, which is not only due to the absence of sources for turbulence, but also because of the inclusion of the additional Alfvén velocity related transport terms, as already demonstrated in Wiengarten et al (2015) for a one-component turbulence model. Furthermore, the perpendicular lengthscales increase with radial distance as turbulence decays, while the parallel lengthscale approaches the resonant one (l res ), which is inversely proportional to the magnetic field strength.…”

“…After an implementation in the MHD modeling framework CRONOS (e.g., Wiengarten et al 2015), the new model, consisting of the generalized turbulence evolution equations self-consistently coupled with those for the large-scale expansion of the solar wind, was validated against the spherically symmetric results obtained earlier by Oughton et al (2011) for a prescribed background solar wind.…”

“…Here we largely follow the approach of Matthaeus et al (1994) and Usmanov et al (2011), extended to incorporate the homogeneous two-component phenomenology presented in Oughton et al (2011) and also retaining terms of theorder ofV U A (Adhikari et al 2015;Wiengarten et al 2015). This leads to the following equations for the fluctuation energies, in the frame corotating with the Sun, …”

“…This has been done for the one-component model by Usmanov et al (2011). Another generalization concerns the removal of the limitation of the model's validity for the super-Alfvénic solar/ stellar wind regimes, which-again for the one-component model-has been achieved recently in a non-self-consistent fashion by Adhikari et al (2015) and fully self-consistently by Wiengarten et al (2015). Naturally, it is desirable to make both extensions also for the two-component turbulence model.…”

“…The equations describing the evolution of the large-scale density and magnetic field are unaffected by the extension to incompressible two-component fluctuations. Neglecting the turbulent electric field, one has (e.g., Usmanov et al 2011;Wiengarten et al 2015),…”