**4.3 Release of magnetic energy by flare eruption**

Not all magnetic energy in the solar atmosphere can be depleted by flare eruptions. For example, the magnetic energy of a potential magnetic field cannot be consumed since no flare eruptions can occur in the potential magnetic field. Only the magnetic energy associated with the electric current in a nonpotential magnetic field can be accessed by flare eruptions. This part of available magnetic energy (energy bundled with the electric current) is called the free magnetic energy [4, 22].

During a flare eruption, a fraction of the total electric current around the PIL is ejected out together with the plasmoid eruption, and the corresponding part of the free magnetic energy is released. After the flare eruption, the total free magnetic energy decreases, and the twisted field lines around the PIL relax to a certain extent owing to the loss of electric current and the depletion of free magnetic energy [11].

A proportion of the released magnetic energy is converted to the electromagnetic emission which manifests as sudden brightening across a broad range of electromagnetic wave spectrum, and that is why the flare phenomenon is named [2]. Other parts of the released magnetic energy are converted to the mechanical energy of the erupted plasmoid and are also carried off by the high-energy particle radiation [2, 4]. The erupted plasmoid might lead to the coronal mass ejections (CMEs) accompanied with solar flares, and the high-energy particles might lead to the solar energetic particle (SEP) events associated with solar flares [12–14].
