  The evolution of nonpotential characteristics of magnetic fields in AR 5747
is presented using Mees Solar Observatory magnetograms taken on Oct. 20, 1989
to Oct. 22, 1989. The active region showed such violent flaring activities
during the observational span that strong X-ray flares took place including a
2B/X3 flare. The magnetogram data were obtained by the Haleakala Stokes
Polarimeter which provides simultaneous Stokes profiles of the Fe I doublet
6301.5 and 6302.5. A nonlinear least square method was adopted to derive the
magnetic field vectors from the observed Stokes profiles and a multi-step
ambiguity solution method was employed to resolve the 180 degree ambiguity.
  From the ambiguity-resolved vector magnetograms, we have derived a set of
physical quantities characterizing the field configuration, which are magnetic
flux, vertical current density, magnetic shear angle, angular shear, magnetic
free energy density and a measure of magnetic field discontinuity MAD (Maximum
Angular Difference between two adjacent field vectors). In our results, all the
physical parameters decreased with time, which implies that the active region
was in a relaxation stage of its evolution. To examine the force-free
characteristics of the field, we calculated the integrated Lorentz force and
and also compared the longitudinal field component with the corresponding
vertical current density. In this investigation, we found that the magnetic
field in this active region was approximately linearly force-free throughout
the observing period. The time variation of the linear force-free coefficient
is consistent with the evolutionary trend of other nonpotentiality parameters.
This suggests that the linear force-free coefficient could be a good indicator
of the evolutionary status of active regions.
