The observation that current patterns in active regions are typically unneutralized has important consequences for flare physics and more generally for our understanding of magnetic fields on the Sun, as outlined by Melrose (1991, 1995) and Leka et al. (1996). First, it indicates that twisting and shearing of the footpoints of coronal magnetic fields are not responsible for the large-scale currents that are observed and, hence, that the in situ storage model for flares is invalid. Magnetic flux emerges at the photosphere with large-scale electric currents already flowing in it and with free energy already present. In the in situ storage picture, observed currents close at or just below the photosphere. Where do they close in the new picture? The latitudinal dependence of the sense of current helicity cannot be explained by standard dynamo theory operating in the bulk of the convection zone, but may be explained by an alternative dynamo model operating at the base of the convection zone (Seehafer 1990). This points to the observed currents being generated (and closing) deep within the Sun, at or near the base of the convection zone. As argued by Melrose (1991), the long inductive time associated with such an extended current system precludes change on the short timescale of a flare, and so current will be conserved during a flare, an important consideration that is missing from most flare models. Melrose (1997) has presented a model for flaring due to reconnection between current carrying loops subject to conservation of both magnetic flux and total
current.
The size of the observed currents also raises interesting questions concerning the appearance of large voltages if the current changes or if the current path changes. Assuming the change occurs on a timescale q, there is an associated electromotive force (EMF) V DL I/q, where L is the inductance of the circuit. The inductance may be estimated by L Dk0 lB100 H for a circuit of length lB108 m. If the current flowing through the corona (IB1012 A) or the inductance changes substantially on the timescale for flux emergence (qB105 s), enormous voltages (V B109 V) are implied.
