Detailed observational characteristics and theoretical interpretations of the EUV wave can be found in recent reviews (Warmuth 2010 Gallagher & Long 2011 Patsourakos & Vourlidas 2012). The first two classes could be interpreted using wave models, while the last one often shows non-wave characteristics.
The classification of EUV waves could be made according to their kinematical behavior, i.e., fast, moderate, and slow waves (Warmuth & Mann 2011). Furthermore, in some cases, both slow and fast wave components could be observed simultaneously (Zhukov & Auchère 2004 Chen & Wu 2011 Shen & Liu 2012b), and they could be interpreted with the so-called hybrid model (Chen et al. However, this is challenged by a few non-wave explanations (Delannée 2000 Harra & Sterling 2003 Attrill et al.
The fast wave scenario has been supported by a number of observational (Veronig et al. However, these basic but important questions still remain. For years, solar physicists have debated the real physical nature (i.e., wave or non-wave) and origin (i.e., flare or coronal mass ejection (CME)) of the EUV wave. On the other hand, it was proposed as the expected coronal counterpart of the chromospheric Moreton wave, which had been explained as the intersection between a fast-mode coronal wave and the chromosphere (Uchida 1968). Since the typical speed (200–400 km s −1 Thompson & Myers 2009) is usually higher than the quiet-Sun sound speed, the EUV wave was initially interpreted as a fast magnetosonic wave (Thompson et al. In recent years, a hot topic of debate in solar physics has been the global extreme-ultraviolet (EUV) wave, which is a broad and diffuse propagating bright structure in the solar corona. Our observations support the hybrid model that includes both fast wave and slow non-wave components. 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. We find that the EUV wave 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). We propose that the different behaviors observed during the interactions may be caused by different speed gradients at the boundaries of the two active regions. The formation of the new wavefront and the transmission could be explained with diffraction and refraction effects, respectively.
When the wave approached AR11459, it transmitted through the active region directly and without reflection. In addition, a reflected wave was also simultaneously observed on the wave incoming side. When the wave approached AR11465, it became weaker and finally disappeared in the active region, but a few minutes later a new wavefront appeared behind the active region, and it was not concentric with the incoming wave. These intriguing phenomena are observed when the wave interacts with two remote active regions, and together they exhibit properties of an EUV wave. We present observations of the diffraction, refraction, and reflection of a global extreme-ultraviolet (EUV) wave propagating in the solar corona.
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