Longitudinal magnetic field gradients and vertical electric currents in active regions with different flare productivity levels

The purpose of the work performed was to search for parameters of longitudinal magnetic field gradients and vertical electric currents, and their values, which could serve as the basis for creating criteria for short-term forecasting of changes in the flare productivity of an active region (AR). In the course of the study, a threshold (critical) value of the average unsigned vertical electric current density ($<|j_z|>$) was identified, equal to 2.7 mA m$^{-2}$; it is shown that in all ARs with high flare activity, the value of $<|j_z|>$ is above the threshold; it is shown that a rapid increase in the parameter $<|j_z|>$ above the critical value, especially in ARs, in which additional ascent of the magnetic flux was recorded during their monitoring time, indicates an increase in AR flare activity in the time interval of 18-20 hours. A threshold value of the transverse component of the longitudinal magnetic field gradient between pairs of sunspots in the AR ($max(\nabla_{\perp}B_z)_{sp}$), equal to 0.118 G km$^{-1}$, was also found. In the AR NOAA 11283, a study of the dynamics of the value made it possible to detect a time delay of 19 hours between the beginning of its stable growth and the time of the beginning of the development of the first of a series of powerful solar flares.