On 13 February 2009, a coronal wave -CME -dimming event was observed in quadrature by the STEREO spacecraft. We analyze this event using a three-dimensional, global magnetohydrodynamic (MHD) model for the solar corona. The numerical simulation is driven and constrained by the observations, and indicates where magnetic reconnection occurs between the expanding CME core and surrounding environment. We focus primarily on the lower corona, extending out to 3R ⊙ ; this range allows simultaneous comparison with both EUVI and COR1 data. Our simulation produces a diffuse coronal bright front remarkably similar to that observed by STEREO/EUVI at 195Å. It is made up of two components, and is the result of a combination of both wave and non-wave mechanisms.The CME becomes large-scale quite low (< 200 Mm) in the corona. It is not, however, an inherently large-scale event; rather, the expansion is facilitated by magnetic reconnection between the expanding CME core and the surrounding magnetic environment. In support of this, we also find numerous secondary dimmings, many far from the initial CME source region. Relating such dimmings to reconnecting field lines within the simulation provides further evidence that CME expansion leads to the "opening" of coronal field lines on a global scale. Throughout the CME expansion, the coronal wave maps directly to the CME footprint.Our results suggest that the ongoing debate over the "true" nature of diffuse coronal waves may be mischaracterized. It appears that both wave and non-wave models are required to explain the observations and understand the complex nature of these events.

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We examine the nature of large-scale, coronal, propagating wave fronts (''EIT waves'') and find they are incongruous with solutions using fast-mode MHD plane-wave theory. Specifically, we consider the following properties: nondispersive single pulse manifestations, observed velocities below the local Alfvén speed, and different pulses which travel at any number of constant velocities, rather than at the ''predicted'' fast-mode speed. We discuss the possibility of a soliton-like explanation for these phenomena, and show how it is consistent with the above-mentioned aspects.

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Recently developed mapping algorithms allow automated tracking of a propagating coronal wave, enabling the finding of reproducible fronts and propagation trajectories. Coronal observations taken by the Transition Region and Coronal Explorer (TRACE ) on 1998 June 13 show a large-scale bright wave front, comparable to ''EIT waves'' seen with the Extreme Ultraviolet Imaging Telescope aboard the Solar and Heliospheric Observatory ( SOHO EIT ). Cross sections measuring density perturbations show roughly Gaussian wave structure, suggesting a single propagating compression front. The wave fronts are also found to propagate nonuniformly, unlike the circular fronts often seen with SOHO EIT. Any perceived dissimilarity between EIT waves and the bright propagating fronts seen by TRACE, however, can be explained by differences in the typical observing sequences of the two instruments.