Case Study of Four Homologous Large-Scale Coronal Waves Observed on 2010 April 28 and 29

On 2010 April 28 and 29, the Solar TErrestrial Relations Observatory B/Extreme Ultraviolet Imager observed four homologous large-scale coronal waves, the so-called EIT-waves, within 8 hr. All waves emerged from the same source active region, were accompanied by weak flares and faint coronal mass ejections, and propagated into the same direction at constant velocities in the range of ~220-340 km s-1. The last of these four coronal wave events was the strongest and fastest, with a velocity of 337 +/- 31 km s-1 and a peak perturbation amplitude of ~1.24, corresponding to a magnetosonic Mach number of Mms ~ 1.09. The magnetosonic Mach numbers and velocities of the four waves are distinctly correlated, suggestive of the nonlinear fast-mode magnetosonic wave nature of the events. We also found a correlation between the magnetic energy buildup times and the velocity and magnetosonic Mach number.

First observations of a dome-shaped large-scale coronal EUV wave

We present first observations of a dome-shaped large-scale EUV coronal wave, recorded by the EUVI instrument onboard STEREO-B on January 17, 2010. The main arguments that the observed structure is the wave dome (and not the CME) are: a) the spherical form and sharpness of the domes outer edge and the erupting CME loops observed inside the dome; b) the low-coronal wave signatures above the limb perfectly connecting to the on-disk signatures of the wave; c) the lateral extent of the expanding dome which is much larger than that of the coronal dimming; d) the associated high-frequency type II burst indicating shock formation low in the corona. The velocity of the upward expansion of the wave dome ($v sim 650$ km s$^{-1}$) is larger than that of the lateral expansion of the wave ($v sim 280$ km s$^{-1}$), indicating that the upward dome expansion is driven all the time, and thus depends on the CME speed, whereas in the lateral direction it is freely propagating after the CME lateral expansion stops. We also examine the evolution of the perturbation characteristics: First the perturbation profile steepens and the amplitude increases. Thereafter, the amplitude decreases with r$^{-2.5 pm 0.3}$, the width broadens, and the integral below the perturbation remains constant. Our findings are consistent with the spherical expansion and decay of a weakly shocked fast-mode MHD wave.