NASA Goddard Space Flight Center
An observation of EUV waves as a counterpart of propagating fast-mode waves high above the solar surface (1.5-3 solar radius)observed by STEREO SECCHI COR1
Coronal "extreme ultraviolet (EUV) waves" are a globally propagating large-scale coronal bright fronts (hereafter CBFs), across the solar disk in EUV passbands. There have been much debate on the physical nature of EUV coronal waves ever since their first discovery in 1996, whether it is real fast-mode waves propagating the low solar corona or a counterpart of expanding coronal mass ejections (CMEs). We present a direct observation of a propagating fast-mode wave across the solar radial background magnetic fields with STEREO SECCHI COR1 Ahead and Behind, associated with propagating CBFs observed by STEREO SECCHI EUVI Ahead and SDO AIA. COR1 observed a CME associated with a M9.3 class flare on 2011 Aug. 4 and it was accompanied by the CBF in the low solar corona. After an impulsive expanding of the CME, a fast-mode wave (hereafter COR1 wave) occurred in the height range of 1.5-3 solar radius, propagated outward from the flare site, and it passed through streamers and coronal holes. Assuming the radial propagation from the initiation site in three-dimensional space\,(cone shape of the wave fronts), an average speed of the COR1 wave is about 300 km/s and this fronts are connected to the CBFs in the low solar corona. It is interesting to note that the streamers show kinked mode oscillation owing to the interaction with the propagating COR1 wave and a kinked mode oscillation of a streamer is linked to a stationary CBF along a boundary of coronal hole. The propagating front of the COR1 wave seems to trigger another CME and outflows, indicating the occurrence of magnetic reconnections and/or energy transfers by fast-mode waves. This is the first evidence for the propagating fast-mode wave across the solar radial background magnetic fields high above the corona, having a decisive effect on the low solar coronal activities as well as CBFs. As a conclusion, a CBF is a counterpart of the fast-mode wave propagation high above the solar corona rather than a counterpart of an expanding CME or a wave propagating on the low solar corona.