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G.S. Choe, C.Z. Cheng (Princeton Plasma Physics Laboratory)
The repetitive process of generation of magnetic flux ropes and their merging is studied in a magnetic arcade system by 2-1/2D numerical MHD simulations. Increase of magnetic shear enables field lines in a magnetic arcade to reconnect and form a magnetic island. In the shear-relaxed lowlying arcade, continuous footpoint shearing can create another island. The two islands merge very quickly to form one bigger island. This process is found to repeat in a time interval on the order of a day. This may explain how homologous flares repetitively take place in the same active region. Depending on the mode of shear-increasing motion, the energy flux through the photosphere is varied when magnetic reconnection is allowed. We will show the Poynting flux distributions in several cases and discuss how the energy exchange through the photosphere can affect the time interval of flaring events. We will also demonstrate that a shear-decreasing motion can cause a reverse magnetic reconnection and destroy the helical structure of the magnetic island.
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