Comparison between probability density functions of vertical electric current in solar active regions based on HMI/SDO and SOT/Hinode data

Abstract

Studying electric currents in solar active regions (AR) is an essential step in understanding solar activity in general and solar flares in particular. In this paper, we compare probability density functions of vertical electric current PDF(|jz|) in several active regions, using HMI/SDO and SOT/Hinode photospheric magnetic field data. We have established that at a high value (above the noise level of |jz| ~9•10³ statampere/cm²) of current structures of ARs these functions are nearly identical. The main difference in PDFs for low (noise) jz is due to differences in sensitivity of these two instruments. We have also found that the criterion of pixel selection from magnetic field strength is inapplicable, and the similarity between PDFs is determined by high jz. For all ARs under study we have calculated the power law exponent of the PDF tail for the two instruments, which coincide within their errors for the current structures with current values above noise level. Thus there is no significant difference as to which instrument is used for analyzing probability density functions in high current parts of ARs where flares are localized.