The Vertical Current Approximation Nonlinear Force-Free Field Code - Description, Performance Tests, and Measurements of Magnetic Energies Dissipated in Solar Flares
Markus J. Aschwanden Submitted: 2016-02-01 11:19
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).
Authors: Markus J. Aschwanden
Publication Status: ApJ Suppl.Ser., subm. 2016 Feb 1
Last Modified: 2016-02-03 09:17