Propagation of Moreton Waves

Abstract

Abstract With the Flare-Monitoring Telescope (FMT) and Solar Magnetic Activity Research Telescope (SMART) at Hida observatory of Kyoto University, 13 events of Moreton waves were captured at H$\alpha$ center, H$\alpha$$\pm$0.5 Å, and H$\alpha$$\pm$0.8 Å wavebands since 1997. With such samples, we have studied the statistical properties of the propagation of Moreton waves. Moreton waves were all restricted in sectorial zones with a mean value of 92$^\circ$. However, their accompanying EIT waves, observed simultaneously with SOHO/EIT at extreme-ultraviolet wavelength, were very isotropic with a quite extended scope of 193$^\circ$. The average propagation speeds of the Moreton waves and the corresponding EIT waves were 664 km s$^{-1}$ and 205 km s$^{-1}$, respectively. Moreton waves propagated either under large-scale close magnetic flux loops, or firstly in the sectorial region where two sets of magnetic loops separated from each other and diverged, and then stopped before the open magnetic flux region. The location swept by Moreton waves had a relatively weak magnetic field as compared to the magnetic fields at their sidewalls. The ratio of the magnetic flux density between the sidewall and the path falls in the range of 1.4 to 3.7 at a height of 0.01 solar radii. Additionally, we roughly estimated the distribution of the fast magnetosonic speed between the propagating path and sidewalls in an event on 1997 November 3, and found a relatively low-fast magnetosonic speed in the path. We also found that the propagating direction of Moreton waves coincided with the direction of filament eruption in a few well-observed events. This favors an interpretation of the “Piston” model, although further studies are necessary for any definitive conclusion.