Introduction

The suggestion that many solar flares are due to the interaction of two or more flux loops interacting within an active region is longstanding (e.g. Heyvaerts, Priest and Rust 1977; Machado et al. 1988). Recently, Nishio et al. (1997) and Hanaoka (1997) used a combination of microwave, soft X-ray and magnetogram observations to demonstrate that a large number of solar flares occur where a new flux loop emerges within an active region and interacts with an existing loop, presumably through magnetic reconnection, producing a solar flare. The structure suggested by these observations is that of the interaction of at least two current and flux carrying loops, each with a footpoint where current emerges from the photosphere and a footpoint where current reenters the photosphere. The relative motion of these loops causes them to intersect and exchange currents and flux through the process of magnetic reconnection. This picture has been expanded into a model by Melrose (1997; hereinafter M97), who explored in detail the implications of the fact that within this model the strengths of currents moving through the footpoints of the loops cannot change significantly over the timescale of a flare. This constraint implies that the energy release in the flares is due solely to a redistribution of current and flux above the photosphere.

The model of M97 relates the geometry of the footpoints of the loops and the currents within the loops to the total energy released by the flare. A proviso is that the dominant contribution to the energy released by the flare must be due to the change in magnetic energy associated with the redistribution of currents between the footpoints of the loops. There is also a change in the magnetic energy associated with transfer of flux between the loops, but it was argued by M97 that this is a smaller effect, and it is ignored here. Using the model of M97, any particular configuration of footpoints can be modeled and an estimate of the energy released can be made. If the energy difference, , between the pre- and post- current transfer states is positive, it is assumed that a flare may occur, with this energy available through magnetic reconnection. If the energy difference is negative, no flare should occur. There is a further condition for a flare to occur: the loop structures must intersect, in order for the reconnection and the current transfer to be possible.

The efficacy of the model of M97 can only be determined through comparison with the observational data on flares. The purpose of this paper is to explore the observable consequences of this model, and to propose strategies whereby existing and future instrumentation may explore the correctness of its predictions. The structure of this paper is as follows. In Section 2, the model for solar flares presented in M97 is outlined briefly. This is followed in Section 3 with the application of the model to a variety of footpoint configurations. Section 4 contains the conclusions that are drawn from this work.

© Copyright Astronomical Society of Australia 1997