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In this work we provide an updated description of the Vertical CurrentApproximation Nonlinear Force-Free Field (VCA-NLFFF) code, which is designed tomeasure the evolution of the potential, nonpotential, free energies, and thedissipated magnetic energies during solar flares. This code provides acomplementary and alternative method to existing traditional NLFFF codes. Thechief advantages of the VCA-NLFFF code over traditional NLFFF codes are thecircumvention of the unrealistic assumption of a force-free photosphere in themagnetic field extrapolation method, the capability to minimize themisalignment angles between observed coronal loops (or chromospheric fibrilstructures) and theoretical model field lines, as well as computational speed.In performance tests of the VCA-NLFFF code, by comparing with the NLFFF code ofWiegelmann (2004), we find agreement in the potential, nonpotential, and freeenergy within a factor of about 1.3, but the Wiegelmann code yields in theaverage a factor of 2 lower flare energies. The VCA-NLFFF code is found todetect decreases in flare energies in most X, M, and C-class flares. Thesuccessful detection of energy decreases during a variety of flares with theVCA-NLFFF code indicates that current-driven twisting and untwisting of themagnetic field is an adequate model to quantify the storage of magneticenergies in active regions and their dissipation during flares. - The VCA-NLFFFcode is also publicly available in the Solar SoftWare (SSW).

the astrophysical journal. supplement series/astrophysical journal. supplement series

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