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Astron. Astrophys. 318, 289-292 (1997)

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1. Introduction

It is commonly believed that electric currents flow in the solar atmosphere and form electric circuits between subphotospheric and coronal layers (Alfvén and Carlqvist, 1967; Alfvén, 1977; Spicer, 1982; Melrose, 1995). Measurements of the photospheric vector magnetic field show positions where the currents cross the photosphere (de La Beaujardière et al., 1993; Hofmann, 1995). The measured total current and current density are in the range of 1011 - 1012 A and 10-3 - 10-2 A m-2, respectively (Hagyard, 1988). It is expected that the electric currents are flowing in so called quasi-separatrix layers (Démoulin et al., 1996). These currents and the corresponding magnetic fields represent the free energy which can be released during solar flares. The magnetic field reconnection and coalescence of electric currents are considered as the mechanisms releasing this energy (Priest, 1994; Tajima et al., 1987). Thus, electric currents play an important role in the solar flare theory as well as in the theory of pre-flare filaments. It was suggested by Van Tend and Kuperus (1978) that the filament can be destabilized by an increase of the electric current flowing in this filament. This idea was generalized by Kaastra (1985), Martens (1986), and by Forbes and Isenberg (1991) who presented models of solar flares. But the question arises: What are the real paths of electric currents in the solar atmosphere and how to determine these paths?

In the following, we first present a new model computing this electric current path and then we use this model for the single and multiple current paths cases.

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© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998