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We suggest a nonlinear resonance mechanism to explain how the Hall term predominates the convection term at the reconnection point during magnetic reconnection quantitatively. Both the case with guide field and that without guide field are run in this simulation. The new findings are as follows: (1) The Hall term compared to the convection term can reach the order of several tens with sharp peaks at the reconnection point in the former case. (2) The frequency range of electrostatic waves at the reconnection point in the former case is broader than that in the latter case. (3) The instantaneous frequency of x or z component of the Hall term can pulse instantly in the former case, and it can exceed the order of 10 in this case. The upward frequency sweeping due to the nonlinear resonance of multiwave coupling is inferred to be responsible for the above simulation results.

Plain Language Summary Magnetic reconnection is a fundamental and important physical process, which plays the key role in both laboratory and space plasma. The concept about magnetic reconnection was first suggested to explain flares observed in the chromosphere in 1940s. However, how the magnetic reconnection is triggered is a long-standing unsolved key problem in the present theory of magnetic reconnection. Traditionally, the whistle wave is suggested to be responsible for the triggering of magnetic reconnection due to its dissipation property. However, it can describe only qualitatively the triggering of magnetic reconnection; therefore, the triggering mechanism of magnetic reconnection is a long-standing unsolved key problem. Recently, two fluid effects are suggested to be important in the Hall magnetic reconnection, and the nonlinear resonance of multiwave coupling is paid an attention to study the triggering mechanism of magnetic reconnection. In this paper, the cascade theory (upward frequency sweeping) due to the nonlinear resonance is used to explain the triggering mechanism of magnetic reconnection for the first time in order to solve a long-standing unsolved key problem in plasma physics based on our simulation results. And the new role of guide field B-g is also found for the first time.