A phenomenological model of coronal mass ejections

A model of coronal mass ejection (CME) is proposed, that is based on the break of equilibrium of twisted magnetic tubes (loops) emerging from the photosphere into the corona. Under the assumption of mass and axial flux conservation in the tube, a phenomenological model describes the loss of equilibrium as a result of a pressure increase in the tube due to its warming and additional magnetic heating when the twist increases in the expanding tube. A fast expansion of the tube to a new equilibrium radius will reduce the density inside the tube and, due to an additional buoyancy force, the tube will be ejected into the corona. The conditions are determined under which a pressure decrease inside a tube, due to the plasma outflow through its ends removes the onset of the eruptive instability. The upward motion of mass and the onset of the eruptive instability are related in the following way: the loops that lose a large amount of mass are not susceptible to an eruptive instability but the loops that lose only a small amount of mass experience an eruptive instability that leads to an ejection of the loop. (C) 2000 COSPAR. Published by Elsevier Science Ltd.