Magnetic field and electric current structure in the chromosphere

Abstract

Three dimensional vector magnetic field structure throughout the chromosphere above an active region is deduced by combining high resolution Hc~ filtergrams with a simultaneous digital magnetogram. An analog model of the field is made with 400 metal wires representing fieldlines which are assumed to outline the Hc~ structure. The height extent of the field is determined from vertical field gradient observations around sunspots, from observed fibril heights and from an assumption that the sources of the field should be largely local. After digitization the magnetic field H matrix is retrieved. Electric current densities j are computed from j curl H. The currents (typically I0 mA m -a) flow in patterns not similar to observed features and not parallel to magnetic fields. Lorentz forces are computed from F--j •The force structures correspond to observed solar features and a series of observed dynamics may be expected: downward motion in bipolar areas in lower chromosphere, an outflow of the outer chromosphere into the corona with radially outward flow above bipolar plage regions (where coronal streamers are observed) and motions of arch filament systems. Observed current structure and magnitude agree well with previous vector magnetograph observations but disagree with theoretical current-free or force-free concepts. A dynamic chromosphere with electromagnetic forces in action is thus inferred from observations.

Electric Currents in the Solar Atmosphere

“…The horizontal electric currents were found to be larger than the vertical current [Kotov , 1971]. Dravins [1974] confirmed early findings made by Crimean astronomers. The average current density is sunspots was found to be about 9×10 −3 A m −2 and about 3×10 −3 A m −2 outside the sunspot outer boundary.…”