Observational and numerical study of the 25 July 2004 event

We study the 25 July 2004 event. By analyzing SOHO EIT images we establish a basic understanding of the large-scale interaction going on during this event. Magnetic reconnection between the expanding CME and the Southern hemispheric active regions (AR) will connect the leading polarities of the two ARs, lead to brightening in the ARs and transport CME field line foot points to distant ARs (observable as dimming at the foot points).We reproduce the large scale interactions during this event using three-dimensional magneto-hydrodynamic (MHD) simulations. We superimpose a magnetic source region that resembles the SOHO MDI images on a basic wind model. By emerging new flux at the centre of this region we initiate a Coronal Mass Ejection (CME). We monitor the evolution of this CME and study its interaction with the source region.