A multiwavelength study of solar flare waves. II. Perturbation characteristics and physical interpretation

Abstract

The study of solar flare waves - globally propagating wave-like disturbances usually observed in Hα as Moreton waves - has recently come back into focus prompted by the observation of coronal waves in the EUV with the SOHO/EIT instrument (``EIT waves"), and in several additional wavelength channels. We study 12 flare wave events in order to determine their physical nature, using Hα, EUV, helium I, SXR and radioheliographic data. In the companion Paper I, we have presented the observational data and have discussed the morphology, spatial characteristics and the kinematics of the different flare wave signatures. The wavefronts observed in the various spectral bands were found to follow kinematical curves that are closely associated, implying that they are signatures of the same physical disturbance. In the present paper, we continue the study with a close examination of the evolution of the common perturbation that causes the different wave signatures, and with a detailed analysis of the metric type II radio bursts that were associated with all flare wave events. The basic characteristics of the waves are deceleration, perturbation profile broadening, and perturbation amplitude decrease. This behavior can be interpreted in terms of a freely propagating fast-mode MHD shock formed from a large-amplitude simple wave. It is shown that this scenario can account for all observed properties of the flare waves in the various spectral bands, as well as for the associated metric type II radio bursts.