Diffraction, Refraction, and Reflection of an Extreme-Ultraviolet Wave Observed During Its Interactions With Remote Active Regions

Abstract

We present observations of the diffraction, refraction, and reflection of a global extreme-ultraviolet (EUV) wave propagating in the solar corona. These intriguing phenomena are observed when the wave interacts with two remote active regions, and they together exhibit the wave property of this EUV wave. When the wave approached AR11465, it became weaker and finally disappeared in the active region, but a few minutes latter a new wavefront appeared behind the active region, and it was not concentric with the incoming wave. In addition, a reflected wave was also observed simultaneously on the wave incoming side. When the wave approached AR11459, it transmitted through the active region directly and without reflection. The formation of the new wavefront and the transmission could be explained with diffraction and refraction effects, respectively. We propose that the different behaviors observed during the interactions may caused by different speed gradients at the boundaries of the two active regions. For the origin of the EUV wave, we find that it formed ahead of a group of expanding loops a few minutes after the start of the loops' expansion, which represents the initiation of the associated coronal mass ejection (CME). Based on these results, we conclude that the EUV wave should be a nonlinear magnetosonic wave or shock driven by the associated CME, which propagated faster than the ambient fast-mode speed and gradually slowed down to an ordinary linear wave. Our observations support the hybrid model that includes both fast wave and slow non-wave components.

Mode Conversion of a Solar Extreme-ultraviolet Wave over a Coronal Cavity

“…New observations of EUV waves with the unprecedentedly high temporal and spatial resolutions often reveal the co-existence of a fast-propagating front ahead of a slow-propagating one (Liu et al 2010;Chen & Wu 2011;Liu et al 2012;Cheng et al 2012, etc.). The slow front is found co-spatial with the CME frontal loop (Dai et al 2012), while the fast front shows wave characteristics such as reflection from a coronal hole or a coronal bright structure (Gopalswamy et al 2009;Li et al 2012;Olmedo et al 2012), diffraction or refraction upon the interaction with a remote active region (Shen et al 2013), and triggering of remote filament oscillations (Dai et al 2012;Zong & Dai 2015). These observations reasonably incorporate both the wave and non-wave components into an individual EUV wave event.…”

Observations of a Quasi-periodic, Fast-Propagating Magnetosonic Wave in Multiple Wavelengths and Its Interaction with Other Magnetic Structures

“…Therefore, we will confine our attention to the QFP wave and the accompanying flare in the present article. Detailed analysis of the global EUV wave has been published very recently by Shen et al (2013).…”

Large-scale Globally Propagating Coronal Waves

“…This behavior was well reproduced by simulations based on geometric acoustics (Uchida, 1968;Uchida et al, 1973;Afanasyev and Uralov, 2011) and 3D MHD simulations (Wang, 2000;Ofman and Thompson, 2002;Terradas and Ofman, 2004). This refracting behavior of coronal waves can now be directly seen with AIA (e.g., Shen et al, 2013).…”

“…These findings have been criticized by Attrill (2010), who claimed that optical illusions due to a misinterpretation of running difference images had been mistaken as wavefronts, but it is difficult to see how that could affect the intensity stack plots, which clearly show the reflected wave. Moreover, the improved cadence brought by SDO/AIA has resulted in numerous further cases of wave reflections at coronal holes, ARs, and bright points (e.g., Li et al, 2012;Olmedo et al, 2012;Shen and Liu, 2012a;Shen et al, 2013, see the animation in Figure 31 for an example), and the reality of the phenomenon is now generally accepted. Kienreich et al (2013) studied three homologous EUV waves using stereoscopic observations from STEREO/EUVI and PROBA2/SWAP, which were all reflected at a coronal hole.…”

“…EUV waves have been observed to transmit into or through ARs (Shen et al, 2013), coronal cavities , and coronal holes , and there has been one report of a Moreton wave transmitting into a coronal hole . The transmitting waves are generally faster than the incident ones (by typically 10 -60%), which is consistent with the higher fast-mode speeds in the structures that are being penetrated.…”