Spatial configuration of highly sheared magnetic structures in active region (NOAA 6659) in 1991 June

In this paper, we analyze first the configuration, especially the reversal features in the H beta chromospheric longitudinal magnetograms in a very flare-active delta group (NOAA 6659). We discuss the possibility of large-scale reversal chromospheric magnetic structures overlapped on the photospheric umbrae after the comparison between the photospheric vector magnetograms and chromospheric longitudinal magnetograms and their forming height difference. We present the possible spatial configuration of the magnetic shear and the relationship with the electric current, and we find that some highly sheared magnetic features of opposite polarity in the active region deviated from the constant-alpha force-free field. The interaction of the newly emerging magnetic flux of opposite polarity with large-scale magnetic structures is the triggering mechanism of a series of powerful flares formed in the lower solar atmosphere.