Solar coronal mass ejections (CMEs) are associated with many dynamical phenomena, among which EIT waves have always been a puzzle. In this Letter MHD processes of CME-induced wave phenomena are numerically simulated. It is shown that as the flux rope rises, a piston-driven shock is formed along the envelope of the expanding CME, which sweeps the solar surface as it propagates. We propose that the legs of the shock produce Moreton waves. Simultaneously, a slower moving wavelike structure, with an enhanced plasma region ahead, is discerned, which we propose corresponds to the observed EIT waves. The mechanism for EIT waves is therefore suggested, and their relation with Moreton waves and radio bursts is discussed.

Ellerman bombs and Type II white-light flares share many common features despite the large energy gap between them. Both are considered to result from local heating in the solar lower atmosphere. This paper presents numerical simulations of magnetic reconnection occurring in such a deep atmosphere, with the aim to account for the common features of the two phenomena. Our numerical results manifest the following two typical characteristics of the assumed reconnection process: (1) magnetic reconnection saturates in ～600-900 s, which is just the lifetime of the two phenomena; (2) ionization in the upper chromosphere consumes quite a large part of the energy released through reconnection, making the heating effect most significant in the lower chromosphere. The application of the reconnection model to the two phenomena is discussed in detail.

This paper reviews our recent progress in the numerical study of coronal mass ejections (CMEs) based on flux rope model, which shows that when the reconnection-favored emerging flux appears either within or ABSTRACT on the outer edge of the filament channel, the flux rope would lose its equilibrium, and be ejected, while a current sheet is formed below the flux rope. For the case with emergence within the filament channel, even small flux is enough to trigger the loss of equilibrium, however, there is a threshold for the emerging flux on the outer edge of the filament channel. Given that anomalous resistivity sets in (e.g. when the current density exceeds a critical value), fast reconnection is resulted in, leading to fast eruption of the flux rope and localized flare (either impulsive-type or LDE-type depending on the height of the reconnection point) near the solar surface. The numerical results can well explain why CMEs are not centered on flares and provide hints for CME-flare spatial and emporal relationships.

Observations indicate that reconnection-favored emerging flux has a strong correlation with coronal mass ejectons (CMEs). Motivated by this observed correlation and based on the flux rope model, an emerging flux trigger mechanism is proposed for the onset of CMEs, using two-dimensional magnetohydrodynamic (MHD) numerical simulations : when such emerging flux emerges within the filament channel, it cancels the magnetic field below the flux rope, leading to the rise of the flux rope (owing to loss of equilibrium) and the formation of a current sheet below it. Similar global restructuring and a resulting rise motion of the flux rope occur also when reconnection-favored emerging flux appears on the outer edge of the

We present a theoretical model for the shock formation that is related to coronal and interplanetary type II radio bursts associated with coronal mass ejections on the basis of the magnetic reconnection model of eruptive solar flares. Coronal type II bursts are usually observed in the metric wavelength range (metric type II bursts), and interplanetary bursts are usually observed in the decametric-hectometric wavelength range (decametrichectometric bursts). Our research shows that the decametric-hectometric type II radio bursts are produced by the piston-driven fast-mode MHD shock that is formed in front of an eruptive plasmoid (a magnetic island in the two-dimensional sense or a magnetic flux rope in the three-dimensional sense), while the metric radio bursts are produced by the reverse fast-mode MHD shock that is formed through the collision of a strong reconnection jet with the bottom of the plasmoid. This reverse shock apparently moves upward as long as the reconnection jet is sufficiently strong and dies away when the energy release of the reconnection stops or weakens significantly. On the other hand, the piston-driven fast shock continues to exist when the plasmoid moves upward. Our model succeeds in explaining the observational result that the piston-driven fast shock that produces decametrichectometric type II bursts moves faster and survives longer than the other shock.