Electric currents and H? emission in two active regions on the sun

Abstract

We investigated the structure of magnetic field and vertical electric currents in two active regions through a comparison of the observed transverse field with the potential field, which was computed according to Neumann boundary-value problem for the Laplace equation using the observed H z -value. Electric currents were calculated from the observations of the transverse magnetic field. There exist two systems of vertical electric currents in active regions: a system of local currents and a global one. The global current is about 2 × 1012 A. In the leading part of the active regions it is directed upward, and in the tail downward. Flare activity is closely connected with the value and direction of both local and global currents: the flares tend to apear in places with upward currents. The luminosity of Hα flocculi is also connected with vertical electric currents; the brighter the flocculi, the more frequently they appear in places of upward electric currents. The sensitivity of Hα emission to the sign of the current suggests that charged particles accelerated in the upper parts of magnetic loops may be responsible for these formations. Joule heating might be important for flocculi, if plasma conductivity is about 5 × 108 c.g.s.e. A model of a flare is suggested based on current redistribution in a system of emerging loops due to changes of loop inductance.