A Numerical Simulation of Coronal Waves Interacting with Coronal Holes. I. Basic Features

Abstract

We developed a new numerical code that is able to perform 2.5D simulations of a magnetohydrodynamic (MHD) wave propagation in the corona, and its interaction with a low density region, such as a coronal hole (CH). We show that the impact of the wave on the CH leads to different effects, such as reflection and transmission of the incoming wave, stationary features at the CH boundary, or formation of a density depletion. We present a comprehensive analysis of the morphology and kinematics of primary and secondary waves, i.e. we describe in detail the temporal evolution of density, magnetic field, plasma flow velocity, phase speed and position of the wave amplitude. Effects like reflection, refraction and transmisson of the wave strongly support the theory that large scale disturbances in the corona are fast MHD waves and build the major distinction to the competing pseudo-wave theory. The formation of stationary bright fronts was one of the main reasons for the development of pseudo-waves. Here we show that stationary bright fronts can be produced by the interactions of an MHD wave with a CH. We find secondary waves that are traversing through the CH and we show that one part of these traversing waves leaves the CH again, while another part is being reflected at the CH boundary inside the CH. We observe a density depletion that is moving in the opposite direction of the primary wave propagation. We show that the primary wave pushes the CH boundary to the right, caused by the wave front exerting dynamic pressure on the CH.

Numerical Simulation of Coronal Waves Interacting with Coronal Holes. III. Dependence on Initial Amplitude of the Incoming Wave

“…In this paper, we focused on the influence of the initial amplitude of the incoming wave on the parameters of the secondary waves. By combining the results of Piantschitsch et al (2018) and those we obtained in this paper, we find first, that the combi-nation of a small CH density and a large initial density amplitude leads to a large phase speed of the secondary waves. Second, we observed that the larger the CH density and the larger the initial wave amplitude, the larger the peak values for the first stationary feature.…”

“…We present simulation results of different fast-mode MHD waves interacting with a CH using a newly developed 2.5 MHD code. In (Piantschitsch et al 2017) we found that the interaction of an MHD wave with a CH leads to the evolution of different secondary waves (reflected, traversing and transmitted waves) and the formation of stationary features. In that study we assumed fixed values for the CH density and the initial density amplitude.…”

“…speed at which the depletion is moving in the negative x-direction. Piantschitsch et al (2018) analysed how the CH density influences the amplitudes and the phase speed of the secondary waves. In this paper, we focused on the influence of the initial amplitude of the incoming wave on the parameters of the secondary waves.…”

“…The analysis of the secondary wave's phase speeds in the simulations shows good agreement with observations, where the authors report waves being reflected and refracted at a CH (Kienreich et al 2013) or being transmitted through a CH . The simulations by Piantschitsch et al (2017) were performed by assuming a fixed initial density amplitude and a fixed CH density. In (Piantschitsch et al 2018, under review) we focused on the comparison of different CH densities and on how they influence the morphology and kinematics of the secondary waves and stationary features.…”

Numerical Simulation of Coronal Waves Interacting with Coronal Holes. II. Dependence on Alfvén Speed Inside the Coronal Hole

“…We use our newly developed code to perform 2.5D simulations of MHD wave propagation and its interaction with low density regions of varying density. In this code we numerically solve the standard homogeneous MHD equations (for detailed description of the equations see Piantschitsch et al (2017)) by applying the so called Total Variation Diminishing Lax-Friedrichs (TVDLF) scheme, first described by Tóth & Odstrčil (1996). This scheme is a fully explicit method and achieves second order accuracy in space and time.…”