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.

STEREO quadrature observations of the 3D structure and driver of a global coronal wave

We present the first observations of a global coronal wave (EIT wave) from the two Solar Terrestrial Relations Observatory (STEREO) satellites in quadra- ture. The waves initiation site was at the disk center in STEREO-B and precisely on the limb in STEREO-A. These unprecedented observations from the STEREO Extreme Ultraviolet Imaging (EUVI) instruments enable us to gain insight into the waves kinematics, initiation and 3D structure. The wave propagates globally over the whole solar hemisphere visible to STEREO-B with a constant velocity of 263+/-16 km/s. From the two STEREO observations we derive a height of the wave in the range of 80-100 Mm. Comparison of the wave kinematics with the early phase of the erupting CME structure indicates that the wave is initiated by the CME lateral expansion, and then propagates freely with a velocity close to the fast magnetosonic speed in the quiet solar corona.