S320p.21 — Estimating Solar Active Region Free Energy from the Minimum Current Corona Model

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Aug 10th at 6:00 PM until 7:30 PM

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Author(s): Graham Barnes1, KD Leka1, Eric Wagner1

Institution(s): 1. NWRA

We employ the Minimum Current Corona (MCC) model to estimate the amount of magnetic free energy injected into the coronal magnetic field of active regions. In the MCC model, each concentration of photospheric magnetic flux is represented by a point source, greatly simplifying the magnetic topology. Advecting an initial partitioning of the flux through a long time series of magnetograms results in a persistent set of sources. Flux domains, bundles of field lines interconnecting pairs of sources, are surrounded by separatrix surfaces. The intersection of two separatrices is a separator field line, which is the site of reconnection in this model. The evolution of the photospheric field causes the sources to also evolve, which would lead to changes in the domain fluxes to maintain a potential field configuration if reconnection could proceed rapidly. However, in the absence of reconnection, currents begin to flow to maintain the initial distribution of domain fluxes. The minimum energy state occurs when currents flow along the separators. The magnitude of the separator currents can be estimated and combined with geometrical properties of the separators to give a lower bound to the magnetic free energy of the system. Starting from an initial potential field configuration, changes in the free energy are presented for time series of data from the Helioseismic and Magnetic Imager (HMI) on NASA's Solar Dynamics Observatory for selected active regions, and the topology of the model field in the vicinity of flare emission is determined.
This work was supported by NASA under contract NNH12CC03C.