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

TL;DR

This study analyzes how non-neutralized electric currents evolve during magnetic flux emergence in solar active regions, revealing that more complex regions with delta spots exhibit higher currents, faster flux emergence, and more intense current injection events.

Contribution

It introduces a new method for quantifying non-neutralized electric currents and links their evolution to the complexity of solar active regions, especially delta spots.

Findings

Active regions with delta spots have higher flux emergence rates.

Peak non-neutralized electric currents are significantly higher in complex regions.

Injection events of electric currents are more frequent and longer in complex 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 $\delta$- 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 $\delta$-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.