On April 28–29 2010 , the Solar Terrestrial Relations Observatory ( STEREO ) -B/Extreme Ultraviolet Imager ( EUVI ) observed four homologous large-scale coronal waves , so-called ‘ EIT-waves ’ , within eight hours .
All waves emerged from the same source active region , were accompanied by weak flares and faint CMEs , and propagated into the same direction at constant velocities in the range of \sim 220 - 340 \mathrm { km s } ^ { -1 } .
The last of these four coronal wave events was the strongest and fastest , with a velocity of 337 \pm 31 \mathrm { km s } ^ { -1 } and a peak perturbation amplitude of \sim 1.24 , corresponding to a magnetosonic Mach number of M _ { \mathrm { ms } } \sim 1.09 .
The magnetosonic Mach numbers and velocities of the four waves are distinctly correlated , suggestive of the nonlinear fast-mode magnetosonic wave nature of the events .
We also found a correlation between the magnetic energy build-up times and the velocity and magnetosonic Mach number .