ANALYSIS OF CHARACTERISTIC PARAMETERS OF LARGE-SCALE CORONAL WAVES OBSERVED BY THE<i>SOLAR-TERRESTRIAL RELATIONS OBSERVATORY</i>/EXTREME ULTRAVIOLET IMAGER

Abstract

The kinematical evolution of four extreme ultraviolet waves, well observed by the Extreme Ultraviolet Imager on board the Solar-Terrestrial Relations Observatory (STEREO), is studied by visually tracking wave fronts as well as by a semi-automatized perturbation profile method, which leads to results matching each other within the error limits. The derived mean velocities of the events under study lie in the range of 220–350 km s−1. The fastest of the events (2007 May 19) reveals a significant deceleration of ≈ − 190 m s−2, while the others are consistent with a constant velocity during wave propagation. The evolution of maximum-intensity values reveals initial intensification of 20%–70% and decays to original levels within 40–60 minutes, while the widths at half-maximum and full-maximum of the perturbation profiles broaden by a factor of two to four. The integral below the perturbation profile remains basically constant in two cases, while it shows a decrease by a factor of three to four in the other two cases. From the peak perturbation amplitudes, we estimate the corresponding magnetosonic Mach numbers Mms, which range from 1.08–1.21. The perturbation profiles reveal three distinct features behind the propagating wave fronts: coronal dimmings, stationary brightenings, and rarefaction regions. All features appear after the wave passage and only slowly fade away. Our findings indicate that the events under study are weak-shock fast-mode magnetohydrodynamic waves initiated by the CME lateral expansion.