Based mainly on the high-resolution data obtained by the one meter New Vacuum Solar Telescope (NVST) at the Fuxian Solar Observatory of Yunnan Observatories of the Chinese Academy of Sciences, Dr. WANG Jincheng and his collaborators investigated the physical nature of globally-propagating waves induced by a small-scale filament eruption. The results were recently published in The Astrophysical Journal.

The globally-propagating waves in the solar atmosphere include Moreton wave in the chromosphere and extreme ultraviolet (EUV) wave in the corona. In general, Moreton wave observed in chromospheric spectral lines (typically in Hα and He I 10830 A) propagates in restricted angles with speeds of 500–1500 km/s. EUV wave discovered in EUV band images propagates in the corona with speeds of about 200-1000 km/s.

The fast EUV waves are expected to be the coronal counterpart of Moreton waves. However, joint observations of Moreton and EUV waves are still relatively rare. More evidence is needed to confirm whether fast EUV waves are the counterpart of Moreton waves in the corona, and to determine the relationship between EUV and Moreton waves. On the other hand, the origin of these waves is still an open question in understanding of these large-scale global perturbations in the solar atmosphere.

Focusing on above issues, Dr. WANG and his collaborators studied an event that a small-scale filament eruption excited simultaneously a Moreton wave and an EUV wave in AR 12740 on May 6, 2019.

Combining simultaneous observations in different EUV and Hα passbands, the researchers studied the kinematic characteristics of Moreton and EUV waves by using the intensity profile technique.

They obtained comparable propagation velocities and similar morphologies of the Moreton and different-passband EUV wave front. They deduced that Moreton and different-passband EUV waves are the perturbations in different temperature-associated layers induced by a coronal magneto-hydrodynamic shock wave.

Besides, the researchers found refracted, reflected, and diffracted phenomena during the propagation of the EUV wave. This identified that EUV wave is the true wave instead of pseudo wave.

By using power-law fittings, they obtained the kinematic characteristics of unaffected, refracted, and diffracted EUV waves. According to the extrapolated magnetic field, they found that an interface between different magnetic systems (magnetic separatrix) is the reason for the refraction, reflection, and diffraction of the EUV wave.