Dynamics of Electric Current’s Parameters in Active Regions on the Sun and Their Relation to the Flare Index

Abstract

Data from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) on the components of the magnetic field vector in the photosphere for 39 active regions (AR) of the 24th solar activity cycle are used to calculate the parameters of the electric current. The time variations in the electric current parameters in the AR over the time the region is within ±35° of the central meridian are studied. An attempt is made to relate the parameters of the current in the photosphere and their dynamics to the level of flare activity of the region. These studies have yielded the following results: (1) The change in the total unsigned current in an AR is synchronous or quasi-synchronous with changes in the magnetic flux; (2) A relation between the total unsigned current and the flare index (FI) exists, but is weak (correlation k = 0.48); (3) The imbalance of the vertical electric currents for all 39 of the AR studied here was low and did not exceed a few percent, which indicates closure of the current structures on all scales within an AR; (4) The highest correlation (k = 0.72) with the flare index is observed for a time averaged absolute value of the density of the vertical electric current; (5) Statistical studies yield a critical level of equal to 2.7 mA/m2: when this level is exceeded in an AR, flares with higher x-ray classes (M and X) are observed and when the current density falls below the threshold value, there is a reduction in the flare productivity of the region; (6) For the example of two regions with an emerging magnetic flux it is shown that pumping magnetic energy into the corona requires some time; the time interval between the jump in and the onset of the development of the first powerful flares in x-ray classes M and X is at least 12-20 hours; (7) The character of the relation between the time variations in the average value of the density of the horizontal current and the imbalance in the vertical current ρjz with the level of flare activity of an AR is more complicated and requires separate, more detailed studies.