(ORDO NEWS) — Researchers led by Dr. Zhou Xinping of the Yunnan Observatory of the Chinese Academy of Sciences and their co-authors have found compelling evidence for coronal waves generated by flares.
Their study was published in The Astrophysical Journal Letters. The results of the study suggest that a broad stream of extreme ultraviolet (EUV) waves, including several wavefronts, must be caused by nonlinear processes of energy release in the accompanying flare.
A solitary, diffuse, and bright disturbance is generally considered to be a fast-moving bow shock and a bow shock caused by the expansion of a coronal mass ejection.
Although this scenario can explain many of the observed features of large-scale coronal waves, it is difficult to determine whether a particular EUV wave is due to a CME or a flare, since the acceleration phase of a coronal mass ejection is usually synchronized with the impulsive phase of the flare.
Using high spatiotemporal resolution observational data from the Solar Dynamics Observatory (SDO/AIA), Zhou Xinping and colleagues found that a wide EUV wave consists of several large-scale wavefronts. This wave flow is difficult to explain using the theory of lateral expansion of a coronal mass ejection.
They found that the physical parameters of the wave flow, such as speed, amplitude, and energy flux, correspond to the classical large-scale EUV wave.
Meanwhile, the results of the analysis showed that the time of the beginning of the acceleration phase of the coronal mass ejection lags behind the time of the appearance of the first wave front. On the contrary, the start time of the wave front slightly lagged behind the start time of the accompanying flare.
Combined with the observational evidence above and the overall period between the accompanying flare and the wavefront, the researchers hypothesized that the flare, and not the coronal mass ejection, caused the wavefront.
This study can serve as a reliable argument in favor of the flare mechanism for the generation of EUV waves. It also provides the first evidence for the interference effect of EUV waves, indicating the true wave nature of the observed disturbance.
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