Role of initial density profiles in simulations of coronal wave-coronal hole interactions

Abstract

Interactions between global coronal waves (CWs) and coronal holes (CHs) reveal many interesting features of reflected waves and coronal hole boundaries (CHB). However, such interactions have scarcely been studied thus far. Magnetohydrodynamic (MHD) simulations can help us to better understand what is happening during these interaction events and thus to achieve a broader understanding of the parameters involved. In this study, we performed the first 2D MHD simulations of a CW–CH interaction that include a realistic initial wave density profile consisting of an enhanced wave component as well as a depleted one. We varied several initial parameters, such as the initial density amplitudes of the incoming wave, the CH density, and the CHB width, which are all based on actual measurements. We analysed the effects of different incident angles on the interaction features and we used the corresponding time-distance plots to detect specific features of the incoming and the reflected waves. We found that the specific combination of a small CH density, a realistic initial density profile, and a sufficiently small incident angle can lead to remarkable interaction features, such as a large density amplitude for the reflected wave and greater phase speed for the reflected wave with respect to the incoming one. The parameter studies in this paper provide a tool for comparing time-distance plots based on observational measurements to those created from simulations. This has enabled us to derive interaction parameters from observed CW–CH interaction events that usually cannot be obtained directly. The simulation results in this study are augmented by analytical expressions for the reflection coefficient of the CW–CH interaction, which allows us to verify the simulations results in an complementary way. This work, with its focus on parameter studies that examine the initial density profile of CWs, is the first of a series of studies aiming to ultimately reconstruct actual observed CW–CH interaction events by means of MHD simulations. These results improve our understanding of the involved interaction parameters in a comprehensive way.