The temporal evolution of non-neutralized electric currents and the complexity of solar active regions

Abstract

We study the evolution of electric currents during the emergence of magnetic flux in the solar photosphere and the differences exhibited between solar active regions of different Hale complexity classes. A sample of 59 active regions was analyzed using a method based on image segmentation and error analysis to determine the total amount of non-neutralized electric current along their magnetic polarity inversion lines. The time series of the total unsigned non-neutralized electric current, $I_{NN,tot}$, exhibit intricate structure in the form of distinct peaks and valleys. This information is largely missing in the respective time series of the total unsigned vertical electric current $I_z$. Active regions with $δ$- spots stand out, exhibiting 1.9 times higher flux emergence rate and 2.6 times higher $I_{NN,tot}$ increase. The median value of their peak $I_{NN,tot}$ is equal to $3.6\cdot10^12$ A, which is more than three times higher than that of the other regions of the sample. An automated detection algorithm was also developed to pinpoint the injection events of non-neutralized electric current. The injection rates and duration of these events were higher with increasing complexity of active regions, with regions containing $δ$-spots exhibiting the strongest and longest events. These events do not necessarily coincide with increasing magnetic flux, although they exhibit moderate correlation. We conclude that net electric currents are injected during flux emergence, but are also shaped drastically by the incurred photospheric evolution, as active regions grow and evolve.