The morphology of flare phenomena, magnetic fields, and electric currents in active regions. I. Introduction and methods

This paper introduces a study of electric current systems in solar active regions and their spatial relationship to sites of electron precipitation and high pressure in flares. The primary purpose of this study is to provide observational evidence for or against the flare models commonly discussed in the literature. We determine the photospheric distribution of vertical currents from vector magnetograms. We use Hα line profiles to identify sites of intense nonthermal electron precipitation into the chromosphere and of high pressure in the overlying corona. By observing complete Ha spectra rather than just narrow-band images, we are able to distinguish between electron precipitation and high-pressure sites in the observed flares. By measuring the full Stokes profiles, we can eliminate magneto-optical effects and make first-order corrections for under-resolution in the analysis. By observing continuum images with both the magnetograms and the Hα spectroheliograms, we are able to achieve coregistration accuracy ≤3″. Finally, by eliminating projection effects in the magnetic data we are able to compute true vertical currents. In this introductory paper we describe the specifics of the instrumentation and data used, which primarily originate from Mees Solar Observatory of the University of Hawaii, and we describe the data analysis methods. We summarize several flare models and describe what each predicts for the relationships of flares to the vertical current systems. In subsequent papers we present observations of flares in particular active regions and interpret the findings in the context of the models discussed in this paper.