NUMERICAL SIMULATION OF AN EUV CORONAL WAVE BASED ON THE 2009 FEBRUARY 13 CME EVENT OBSERVED BYSTEREO

Abstract

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.

On the Nature and Genesis of EUV Waves: A Synthesis of Observations from SOHO, STEREO, SDO, and Hinode (Invited Review)

“…Irrespective of their initial speeds or deceleration profiles, these waves ended up travelling within a rather narrow speed range of 180-380 km s −1 which is consistent with the fast mode speed over the quiet Sun (e.g., Wang, 2000;Wu et al, 2001;Cohen et al, 2009;Schmidt and Ofman, 2010;Downs et al, 2011;Zhao et al, 2011). Therefore, the kinematics of the observed waves are consistent with fast-mode waves.…”

“…Observations of EUV waves revealed a series of features which strongly appeal to pseudo-wave interpretations (Attrill et al, 2007a(Attrill et al, ,b, 2009Cohen et al, 2009;Zhukov, Rodriguez, and de Patoul, 2009;Dai et al, 2010;Schrijver et al, 2011;Warmuth and Mann, 2011). These include stationary brightenings, large-scale secondary dimmings and erratic (including a series of accelerations and decelerations) or "slow" (i.e.…”

“…According to the hybrid interpretation, there are two 'EUV waves'. A sharp outer front consistent with a fast-MHD shock and considered the coronal counterpart of the Moreton wave, and an inner diffuse front consistent with a pseudo-wave and considered the 'typical' EUV wave (Chen et al, 2002;Chen, Fang, and Shibata, 2005;Zhukov and Auchère, 2004;Cohen et al, 2009;Pomoell, Vainio, and Kissmann, 2008). The latter is the key weakness of this interpretation, as (2000)).…”

Large-scale Globally Propagating Coronal Waves

“…MHD simulations, fast-mode waves that were launched by eruptions were found to be consistent with many aspects of coronal EUV waves (e.g., Wang, 2000;Wu et al, 2001Wu et al, , 2005Pomoell et al, 2008;Wang et al, 2009;Cohen et al, 2009;Schmidt and Ofman, 2010, see middle panel in Figure 41 for an example). Of course, the results of numerical models must be interpreted with care, since all of them have to make some simplifying assumptions.…”

“…The models consistently show that the fast outer front is a fast-mode MHD wave (or shock), while there is a larger diversity for the interpretation of the inner front. The latter is variously attributed to plasma compression due to the erupting/expanding CME (Cohen et al, 2009;Downs et al, 2011), a compression front associated with a current shell , a slow-mode wave (Wu et al, 2005), a quite complex combination of slow-mode shocks and velocity vortices , or due to a wave launched by the collision between the flow behind the flux rope and the flux rope itself (Pomoell et al, 2008).…”