Evolution of Two EIT/Hα Moreton Waves

Abstract

Since the discovery of EIT waves, questions have remained about the driver of these disturbances and their association with the chromospheric Moreton waves. In order to resolve some of these issues, two flare-associated transient events (1997 November 3 and 1998 May 2) observed simultaneously in Hα and EIT are analyzed. The cospatiality of Moreton and EIT wave fronts is established, and a deceleration of the disturbances is found in both events. In the case of 1998 May 2, a detailed analysis of the evolution of the Moreton wave, its kinematics, and perturbation profile is carried out. The results—deceleration, broadening, and decrease of intensity of the profiles—favor the fast-mode shock ("blast wave") scenario over the coronal mass ejection-associated magnetic field evolution hypothesis.