Coronal electric currents produced by photospheric motions

Abstract

Due to its high electrical conductivity along field lines, the corona provides an electric coupling between those remote points in the photosphere which are linked by coronal lines of force. This coupling essentially acts as a shunt for potential differences induced between such points by the electromotive fields created by photospheric motions. As a result, important coronal currents are driven. This paper studies the implications of this idea for a model which schematizes both the magnetic configuration and the photospheric motions observed in flare producting regions. In this particular geometry, coronal currents would be mainly driven along a sheet, whose trace in the plane of the photosphere would look as a two-ribbon structure on both sides of an inversion line of the photospheric polarity. We show that vertical currents of the order of 10⁻², 10⁻¹ A m⁻² can be generated, and possibly interrupted if the photospheric flow velocity exceeds about 1 km s⁻¹, then releasing the 10³² ergs of magnetic energy previous stored in the circuit.