The kinematical evolution of four EUV waves , well observed by the Extreme UltraViolet Imager ( EUVI ) onboard the Solar-Terrestrial Relations Observatory ( STEREO ) , is studied by visually tracking the wave fronts as well as by a semi-automatized perturbation profile method leading to results matching each other within the error limits .
The derived mean velocities of the events under study lie in the range of 220–350Â km s ^ { -1 } .
The fastest of the events ( May 19 , 2007 ) reveals a significant deceleration of \approx - 190  m s ^ { -2 } while the others are consistent with a constant velocity during the wave propagation .
The evolution of the maximum intensity values reveals initial intensification by 20 up to 70 % , and decays to original levels within 40–60Â min , while the width at half maximum and full maximum of the perturbation profiles are broadening by a factor of 2 – 4 .
The integral below the perturbation profile remains basically constant in two cases , while it shows a decrease by a factor of 3 – 4 in the other two cases .
From the peak perturbation amplitudes we estimate the corresponding magneto-sonic Mach numbers M _ { ms } which are in the range of 1.08–1.21 .
The perturbation profiles reveal three distinct features behind the propagating wave fronts : coronal dimmings , stationary brightenings and rarefaction regions .
All of them appear after the wave passage and are only slowly fading away .
Our findings indicate that the events under study are weak shock fast-mode MHD waves initiated by the CME lateral expansion .