  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 dome's 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.
