Simulation of the Collision of Magnetic Flux Tubes in the Quiet Solar Photosphere

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Abstract
Recent high-resolution photospheric magnetograms made with the SOHO/Michelson Doppler Imager instrument and the Swedish Vacuum Solar Telescope on La Palma show that concentrations of magnetic flux in the quiet photospheric network of the solar photosphere are highly dynamic objects with small-scale substructure. These observations reveal many details in the dynamics of flux emergence, fragmentation, and cancellation. In order to understand such phenomena we investigate the dynamics of two colliding magnetic flux tubes in weakly ionized plasmas with high plasma beta (β 1), using the three-dimensional neutral-MHD equations. First we investigate the collision of two parallel flux tubes for the two cases of partial and complete magnetic reconnection. We find that, when one flux tube with weak current and small radius collides with another flux tube with strong current and large radius, the weak-current flux tube splits into two small flux tubes because of magnetic reconnection. We also find that the collision of magnetic flux tubes with weak current leads to the emission of strong fast magnetosonic waves, resulting in shock formation, while the collision site of two strong-current loops shows no strong wave emission. Next we investigate the collision of two noncollinear flux tubes with X-type configuration, taking into account the effect of density inhomogeneity along the flux tubes due to gravity. We find strong upward plasma flows along the flux tubes and also shock wave emission from the X-type collision region. Finally we discuss the application of these simulation results to coronal heating.