Topological Estimates of Free-Energy Build-up in Active Regions

Details Topological Estimates of Free-Energy Build-up in Active Regions Topological Estimates of Free-Energy Build-up in Active Regions

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsh31b..02l&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #SH31B-02

Physics

7519 Flares, 7526 Magnetic Reconnection (2723, 7835)

Scientific paper

There is a growing consensus that slow evolution of an active region's photospheric flux leads to a build-up in the energy of its coronal field. The anchoring of coronal field lines to the photosphere defines a connectivity between photospheric footpoints of opposing polarities. Due to the corona's extremely high electrical conductivity these connections remain unchanged even as the footpoints move. To estimate the energy stored this way, we group photospheric footpoints into unipolar source regions and reduce the pointwise connectivity map to a matrix of connections between regions. The flux in each such connection must remain fixed even as the source regions evolve. One coronal magnetic field, called the flux constrained equilibrium, has the minimum possible energy for a specified connectivity. The free energy in this equilibrium provides a lower bound on the free energy in the actual field. We obtain such a free-energy lower bounds for several observed active regions. Source regions are defined in a magnetogram (MDI) time sequence of an active region. As the sources evolve the connectivity in a potential field will change, however, the actual connectivity will not. The growing disparity between the two is used to estimate the free energy stored in the coronal field. Flare reconnection will release some portion of this stored energy by changing some of the connectivities. We compare these estimates with observational signatures of energy release. This work supported by NASA's Living with a Star Program and by AFOSR.

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