Coincidence between Hα flare kernels and peaks of observed longitudinal electric current densities

Large-scale filtergrams of a hitherto neglected class 1B flare were compared with previously published vector magnetograms and maps of photospheric longitudinal electric current density (Hagyard et al., 1985). The vector magnetic fields were mapped simultaneously with the eruption of this flare. The authors found a coincidence, to within the plus or minus 2" registration accuracy of the data, between the flare kernels and the locations of maximum shear and of peak values in the longitudinal electric current density. The kernels brighten in a way that implies that the preflare heating and the main release of flare energy are spatially coincident within the limits of resolution ( identical with 2"). A pronounced magnetic shear exists in the vertical direction at the location of the strongest flare kernels. Evidence is provided that the electric currents could be maintained by the energy stored in the sheared transverse magnetic field and that the amount of energy released is proportional to the amount stored. These circumstances are consistent with theories in which flares are triggered by plasma instabilities caused by surplus electric currents.