Modelling the Interaction of Alfvénic fluctuations with Coronal Mass Ejections in the low solar corona

Abstract

Alfvénic fluctuations of various scales are ubiquitous in the solar wind, with their non-linear interactions and eventual cascade resulting in an important heating mechanism to accelerate the solar wind via turbulent heating. Such fluctuations are also present in other transient & coherent plasma structures such as Coronal Mass Ejections (CMEs), and exhibit varying properties as compared to the solar wind plasma. In this study we investigate the interactions between solar wind Alfvénic fluctuations and CMEs using MHD simulations. We use an ideal magnetohydrodynamic (MHD) model with an adiabatic equation of state. An Alfvén pump wave is injected into the quiet solar wind by perturbing the transverse magnetic field and velocity components, and a CME is injected by inserting a flux-rope modelled as a magnetic cloud into the quasi-steady solar wind.We observe that upstream Alfvén waves experience a decrease in frequency and change in the wave vector direction due to the non-spherical topology of the CME shock front. The CME sheath inhibits the transmission of low frequency fluctuations due to the presence of non-radial flows in this region. The frequency of the solar wind fluctuations also affect the steepening of MHD fast waves causing the CME shock propagation speed to vary with the solar wind fluctuation frequencies.