Tests of the Force-free State of the Photosphere and Chromosphere

Graham Barnes, K.D. Leka & Thomas T. Metcalf

We test the hypothesis that the magnetic field above an active region 
becomes force-free in the chromosphere.  We focus here on recent 
observations from the Imaging Vector Magnetograph (IVM) at Mees Solar 
Observatory of an active region which was small enough to be entirely 
within the field of view, but large enough to be of interest.  Vector 
magnetic flux maps are determined from the Na D-1 line formed in the low

chromosphere, and from the FeI line in the photosphere.  By considering
the magnetic free energy, the twist parameter alpha, and the vertical 
current density, we apply three tests of the degree to which the 
magnetic fields are forced, two global and one local.

This work is funded by AFOSR contract F49620-03-C-0019, and NASA grant
NAG5-12466.