The kinematics of a globally propagating disturbance ( also known as an “ EIT wave ” ) is discussed using Extreme UltraViolet Imager ( EUVI ) data from Solar Terrestrial Relations Observatory ( STEREO ) .
We show for the first time that an impulsively generated propagating disturbance has similar kinematics in all four EUVI passbands ( 304 , 171 , 195 , and 284 Å ) .
In the 304 Å passband the disturbance shows a velocity peak of 238 \pm 20 km s ^ { -1 } within \sim 28 minutes of its launch , varying in acceleration from 76 m s ^ { -2 } to -102 m s ^ { -2 } .
This passband contains a strong contribution from a Si xi line ( 303.32 Å ) with a peak formation temperature of \sim 1.6 MK .
The 304 Å emission may therefore be coronal rather than chromospheric in origin .
Comparable velocities and accelerations are found in the coronal 195 Å passband , while lower values are found in the lower cadence 284 Å passband .
In the higher cadence 171 Å passband the velocity varies significantly , peaking at 475 \pm 47 km s ^ { -1 } within \sim 20 minutes of launch , with a variation in acceleration from 816 m s ^ { -2 } to -413 m s ^ { -2 } .
The high image cadence of the 171 Å passband ( 2.5 minutes compared to 10 minutes for the similar temperature response 195 Å passband ) is found to have a major effect on the measured velocity and acceleration of the pulse , which increase by factors of \sim 2 and \sim 10 , respectively .
This implies that previously measured values ( e.g. , using EIT ) may have been underestimated .
We also note that the disturbance shows strong reflection from a coronal hole in both the 171 and 195 Å passbands .
The observations are consistent with an impulsively generated fast-mode magnetoacoustic wave .