Interaction of EIT Waves with Coronal Active Regions

Abstract

Large-scale coronal waves associated with flares were first observed bythe Solar and Heliospheric Observatory (SOHO) Extreme ultravioletImaging Telescope (EIT). We present the first three-dimensional MHDmodeling of the interaction of the EIT waves with active regions and thepossibility of destabilization of an active region by these waves. Theactive region is modeled by an initially force-free, bipolar magneticconfiguration with gravitationally stratified density. We include finitethermal pressure and resistive dissipation in our model. The EIT wave islaunched at the boundary of the region, as a short time velocity pulsethat travels with the local fast magnetosonic speed toward the activeregion. We find that the EIT wave undergoes strong reflection andrefraction, in agreement with observations, and induces transientcurrents in the active region. The resulting Lorentz force leads to thedynamic distortion of the magnetic field and to the generation ofsecondary waves. The resulting magnetic compression of the plasmainduces flows, which are particularly strong in the current-carryingactive region. We investigate the effect of the magnetic fieldconfiguration and find that the current-carrying active region isdestabilized by the impact of the wave. Analysis of thethree-dimensional interaction between EIT waves and active regions canserve as a diagnostic of the active region coronal magnetic structureand stability.