The Vertical Current Approximation Nonlinear Force-Free Field Code - Description, Performance Tests, and Measurements of Magnetic Energies Dissipated in Solar Flares

TL;DR

This paper introduces an updated VCA-NLFFF code for measuring magnetic energies in solar flares, highlighting its advantages over traditional methods, and demonstrating its effectiveness through performance tests and energy measurements.

Contribution

The paper presents an improved VCA-NLFFF code that overcomes limitations of traditional NLFFF methods, with enhanced accuracy, speed, and ability to measure energy changes during solar flares.

Findings

VCA-NLFFF agrees with Wiegelmann's code within a factor of 1.3 for energy measurements.

The code detects energy decreases in most solar flares, confirming magnetic energy dissipation.

The VCA-NLFFF code is publicly available in Solar SoftWare.

Abstract

In this work we provide an updated description of the Vertical Current Approximation Nonlinear Force-Free Field (VCA-NLFFF) code, which is designed to measure the evolution of the potential, nonpotential, free energies, and the dissipated magnetic energies during solar flares. This code provides a complementary and alternative method to existing traditional NLFFF codes. The chief advantages of the VCA-NLFFF code over traditional NLFFF codes are the circumvention of the unrealistic assumption of a force-free photosphere in the magnetic field extrapolation method, the capability to minimize the misalignment angles between observed coronal loops (or chromospheric fibril structures) and theoretical model field lines, as well as computational speed. In performance tests of the VCA-NLFFF code, by comparing with the NLFFF code of Wiegelmann (2004), we find agreement in the potential, nonpotential, and free energy within a factor of about 1.3, but the Wiegelmann code yields in the average a factor of 2 lower flare energies. The VCA-NLFFF code is found to detect decreases in flare energies in most X, M, and C-class flares. The successful detection of energy decreases during a variety of flares with the VCA-NLFFF code indicates that current-driven twisting and untwisting of the magnetic field is an adequate model to quantify the storage of magnetic energies in active regions and their dissipation during flares. - The VCA-NLFFF code is also publicly available in the Solar SoftWare (SSW).