Propagation Speed of a Magnetic Flux-tube Soliton with Electric Current

We present some results of a magnetic flux-tube soliton propagating along a current loop surrounded by a weakly ionized plasma, by using a 3-D Neutral-MHD simulation code. When the velocity of mass flows outside the current loop exceeds about 0.6_A, the magnetic pulse behaves as an isolated string wave which is called a curved soliton, propagating with a velocity less than that one of exterior mass flow. The propagation speed of the magnetic flux-tube soliton is studied by changing the intensity of the electric current along the flux tube, which usually cannot be observed directly. It is found that the soliton speed decreases proportionally to the increment of the electric current, and the speed is independent of the direction of the electric current. We can estimate the current intensity inside a magnetic flux-tube soliton by observations of the soliton speed and the external plasma flow velocity. These results should be compared with recent high-resolution observations of moving magnetic features (MMFs) observed near sunspots.