Annihilation of magnetic helicity: A new model for solar flare onset Original Research Article

Although magnetic reconnection is believed to be a key process for solar flares, the onset mechanism of flares remains as a long-standing problem. In this paper, we propose a new model for solar flares, in which magnetic reconnection converts oppositely-sheared field into the shear-free field. This process can be understood as the annihilation of magnetic helicities with different signs, and it is consistent with the recent results of the helicity observations. Numerical simulations were carried, which show that, if the helicity is sharply reversed within a magnetic arcade, reconnection quickly grows in the helicity inversion layer, driving explosive dynamics. The explosive process appears as a result of nonlinear instability, which grows faster than exponentially with time. Based on the results, we predict that the coexistence of the positive and negative helicity is crucial for the onset of flares.