We present the first SDO AIA observations of a global coronal EUV disturbance ( so-called “ EIT wave ” ) revealed in unprecedented detail .
The disturbance observed on 2010 April 8 exhibits two components : one diffuse pulse superimposed on which are multiple sharp fronts that have slow and fast components .
The disturbance originates in front of erupting coronal loops and some sharp fronts undergo accelerations , both effects implying that the disturbance is driven by a CME .
The diffuse pulse , propagating at a uniform velocity of 204– 238 \mathrm { km } \mathrm { s } ^ { -1 } with very little angular dependence within its extent in the south , maintains its coherence and stable profile for \sim 30 minutes .
Its arrival at increasing distances coincides with the onsets of loop expansions and the slow sharp front .
The fast sharp front overtakes the slow front , producing multiple “ ripples ” and steepening the local pulse , and both fronts propagate independently afterwards .
This behavior resembles the nature of real waves .
Unexpectedly , the amplitude and FWHM of the diffuse pulse decrease linearly with distance .
A hybrid model , combining both wave and non-wave components , can explain many , but not all , of the observations .
Discoveries of the two-component fronts and multiple ripples were made possible for the first time thanks to AIA ’ s high cadences ( \leq 20 s ) and high signal-to-noise ratio .