A Solar Flare Model Based on Magnetic Reconnection between Current‐carrying Loops

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A model for solar flares is proposed in which the flare energy is the magnetic energy released when two current-carrying flux loops reconnect to form two new current-carrying flux loops between the original four footpoints. It is assumed that a magnetic flux, ΔΨ, and an electric current, ΔI, are transferred during the reconnection, subject to the constraint that the flux and the current at each footpoint are unchanged. The change in the magnetic energy is separated into parts due to the transfer of current and of "potential" field, and the latter is neglected (although the argument for doing so is a weak one). The current transferred, ΔI, is assumed equal to its maximum possible value, which is the weaker of the two currents in the initial flux loops. The change in magnetic energy is calculated for some specific simple configurations of the spots (footpoints of the loops). Some favorable configurations for energy release are when a positive polarity spot is near a negative polarity spot (so that one of the final loops is very small) and when the two initial loops are at a large angle to each other. The model allows reconnection only between loops with the same handedness (the sign of the helicity ∝I/Ψ) and the handedness is preserved during reconnection. Observational evidence that there is a preferred handedness for coronal magnetic structures suggests that this requirement of the model is automatically satisfied, but specific data on the helicity in active regions is less conclusive. It is energetically favorable for overlapping colinear loops to reconnect to form a longer and a shorter (nested) loop, and it is suggested that very long loops connecting different active regions form through a sequence of such reconnections involving ephemeral flux loops that emerge between the active regions.