Nature of coronal mass ejection formation: current state of researches and recent results
A brief review of the current state of researches allows us to conclude that magnetic flux tubes (magnetic flux ropes) play a central role in coronal mass ejection formation (CME). However, a question is still unanswered as to whether all CMEs can be divided into two types, namely, impulsive and gradual ones. It would mean existence of at least two different mechanisms of CME formation. The presence of gradual CMEs is established reliably enough. Impulsive CMEs are distinguished from gradual ones by initial phase of their formation. It is suggested that a magnetic tube (magnetic flux rope) that emerges from the convection zone with great velocity and is filled with relatively cold plasma plays a key role in CME formation. Such a probability was theoretically predicted.
In UV channels (193 Å, 211 Å), the magnetic tube with cold low-density plasma must look as a low-brightness region moving from the solar surface, i.e., as a cavity. When density is higher than that of ambient plasma, the ejected cold plasma can have high brightness in the Нα line and 1700 Å channel, similarly to an active prominence. We consider examples of impulsive CME formation in these two cases.
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