Impulsive Flux Transfer Events and Solar Flares

Abstract

Experimental and theoretical aspects of the fundamental process of magnetic flux transfer (' field line reconnection ') are reviewed. Explosively rapid events are observed in a laboratory magnetoplasma device designed to test certain aspects of neutral point theories of the solar flare mechanism. In these events, ultra-fast release of magnetic energy through reconnection of field lines is effected by a conduction mode instability in which an abrupt upward transition to anomalous resistivity takes place in the neighbourhood of the X-point. The events are triggered when the X-point current density exceeds the conduction mode instability threshold. The energy that is released is that which is associated with the induced current system that supports field line reconnection under ordinary quiescent conditions. Many characteristics of the laboratory events and their associated phenomena, when appropriately scaled, show remarkable agreement with corresponding flare observational data. Some new directions for further development of flare theory are therefore recommended. These experiments indicate that a number of assumptions commonly made in theoretical analysis of the reconnection process are inappropriate. The flux transfer process can be well understood theoretically in terms of a simple circuit analogue which models the laboratory process.

Laboratory Experiments on Reconnection in Current Sheets

“…18) (Machado et al, 1983), is quite relevant here. We believe this is the first time the 3-D separator-separatrix structure, originally proposed by Sweet (1958), has been explicitly considered other than in several papers by our colleagues and ourselves (Bratenahl and Baum, 1976b;Baum et al, 1978aBaum et al, , 1979Bratenahl, 1980, 1982).…”

Reconnection of magnetic field lines in viscous conducting fluids

“…Recently, Bratenahl and Baum [1975], on the basis of their laboratory experiments of magnetic merging, raised doubts about the validity of Sweet's postulation of the formation of a current layer. On the other hand, the point of view that resistivity only serves to determine the size of the diffusion core seems to be becoming accepted (see the comprehensive review by Vasyliunas [1975]).…”