Loop coalescence in flares and coronal X-ray brightening

In connection with recent direct observations of interconnecting coronal loops, loop coalescence is being considered as a possibly important process for solar flares and coronal X-ray brightening phenomena. In the present investigation, it is proposed that the nonlinear development of the coalescence instability of current loops provides a coherent explanation of such observations and a phenomenon reported by Forrest et al. (1982), who observed amplitude oscillations in gamma-ray emission from the impulsive phase of a solar flare. It is pointed out that the present theory also offers a quantitative and natural explanation of such known characteristics as the impulsive nature of flares, the time scale of the impulsive phase, intense heating by flares, and formation of the high-energy tail of particle distribution. A plasma configuration which is unstable against the tearing and subsequent coalescence instabilities is studied.