Statistical Analysis of Large-Scale EUV Waves Observed by STEREO/EUVI

Abstract

We statistically analyzed the kinematical evolution and wave pulse characteristics of 60 strong large-scale EUV wave events that occurred during January 2007 to February 2011 with the STEREO twin spacecraft. For the start velocity, the arithmetic mean is 312±115 km s−1 (within a range of 100 – 630 km s−1). For the mean (linear) velocity, the arithmetic mean is 254±76 km s−1 (within a range of 130 – 470 km s−1). 52 % of all waves under study show a distinct deceleration during their propagation (a≤−50 m s−2), the other 48 % are consistent with a constant speed within the uncertainties (−50≤a≤50 m s−2). The start velocity and the acceleration are strongly anticorrelated with c≈−0.8, i.e. initially faster events undergo stronger deceleration than slower events. The (smooth) transition between constant propagation for slow events and deceleration in faster events occurs at an EUV wave start-velocity of v≈230 km s−1, which corresponds well to the fast-mode speed in the quiet corona. These findings provide strong evidence that the EUV waves under study are indeed large-amplitude fast-mode MHD waves. This interpretation is also supported by the correlations obtained between the peak velocity and the peak amplitude, impulsiveness, and build-up time of the disturbance. We obtained the following association rates of EUV wave events with other solar phenomena: 95 % are associated with a coronal mass ejection (CME), 74 % to a solar flare, 15 % to interplanetary type II bursts, and 22 % to coronal type II bursts. These findings are consistent with the interpretation that the associated CMEs are the driving agents of the EUV waves.