FIRST EVIDENCE OF COEXISTING EIT WAVE AND CORONAL MORETON WAVE FROM SDO/AIA OBSERVATIONS

"EIT waves" are a globally propagating wavelike phenomenon. They were often interpreted as fast-mode magnetoacoustic waves in the corona, despite various discrepancies between the fast-mode wave model and observations. To reconcile these discrepancies, we suggested that "EIT waves" are the apparent propagation of the plasma compression due to successive stretching of the magnetic field lines pushed by the erupting flux rope. According to this model, an EIT wave should be preceded by a fast-mode wave, which, however, had rarely been observed. With the unprecedented high cadence and sensitivity of the Solar Dynamics Observatory observations, we discern a fast-moving wave front with a speed of 560 km s(-1) ahead of an EIT wave, which had a velocity of similar to 190 km s(-1), in the "EIT wave" event on 2010 July 27. The results, suggesting that "EIT waves" are not fast-mode waves, confirm the prediction of our field-line stretching model for an EIT wave. In particular, it is found that the coronal Moreton wave was similar to 3 times faster than the EIT wave, as predicted.