Photospheric Injection of Magnetic Helicity: Connectivity--based Flux Density Method

TL;DR

This paper introduces a new connectivity-based method to accurately map the distribution of magnetic helicity flux in solar active regions, improving upon previous proxies by incorporating magnetic field line connectivity.

Contribution

The study develops and tests a novel helicity flux density proxy that accounts for magnetic field connectivity, enhancing the accuracy of helicity injection measurements in solar active regions.

Findings

Connectivity-based proxy outperforms previous methods in accuracy.

Method validated on various models and MHD simulations.

Provides a better tool for studying magnetic helicity in solar activity.

Abstract

Magnetic helicity quantifies how globally sheared and/or twisted is the magnetic field in a volume. This quantity is believed to play a key role in solar activity due to its conservation property. Helicity is continuously injected into the corona during the evolution of active regions (ARs). To better understand and quantify the role of magnetic helicity in solar activity, the distribution of magnetic helicity flux in ARs needs to be studied. The helicity distribution can be computed from the temporal evolution of photospheric magnetograms of ARs such as the ones provided by SDO/HMI and Hinode/SOT. Most recent analyses of photospheric helicity flux derive an helicity flux density proxy based on the relative rotation rate of photospheric magnetic footpoints. Although this proxy allows a good estimate of the photospheric helicity flux, it is still not a true helicity flux density because it does not take into account the connectivity of the magnetic field lines. For the first time, we implement a helicity density which takes into account such connectivity. In order to use it for future observational studies, we test the method and its precision on several types of models involving different patterns of helicity injection. We also test it on more complex configurations - from magnetohydrodynamics (MHD) simulations - containing quasi-separatrix layers. We demonstrate that this connectivity-based helicity flux density proxy is the best to map the true distribution of photospheric helicity injection.