A two-dimensional magnetohydrodynamics simulation with three components is carried out to explore the driven reconnection processes at the dayside magnetopause. The numerical results show significant enhancements of the magnetic field strength B and the By component at the centers of the recurrent plasmoid-like structures. Such features are in line with the signatures of flux transfer events which are envisaged as passages of magnetic flux tubes. The evolution of the topological structure in reconnected flux tubes is investigated in terms of the principle of magnetic helicity. It is found that the total magnetic helicity in the domain increases as time elapses due to the transportation of magnetic helicity flux through the system boundaries and a peak value of the magnetic helicity density h always occurs in the central region of the reconnected flux tube. Furthermore, the gradual accumulation of h in the current sheet is associated with the accumulated magnetic flux which is carried into this region by the plasma inflow. The concentration of the helicity density h in the core of a flux tube arises from the enhancement of the axial field By, which is associated with the continuous addition of By flux to the domain. The present results indicate that the occurrence of the flux rope structure in the vicinity of the magnetopause might be related to the solar wind plasma flow.

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[Abstract] Based on a previous two-dimension and three-component MHD numerical simulation, this paper analyses the evolution of magnetic helicity of various magnetic structures in the magnetotail. The results indicate that, in a driven magnetic reconnection process generated by the dawn-dusk electric field in the magnetotail, the transportation of magnetic helicity flux via the boundaries of system is the direct cause of the change of the total magnetic helicity in the system. The various initial distributions of magnetic helicity density and the transportation of magnetic helicity flux may lead to various evolutions of magnetic helicity density in the neutral sheet region, and could result in the formation of various magnetic structures.

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