STOKES PROFILE ANALYSIS AND VECTOR MAGNETIC-FIELDS .5. THE MAGNETIC-FIELD STRUCTURE OF LARGE SUNSPOTS OBSERVED WITH STOKES-II

Observations with the Stokes II polarimeter of four large sunspots during 1980 have been inverted to obtain the vector magnetic field structure in the photosphere. Features of the derived vector fields in these sunspots are (1) the azimuthal variation of the field is unexpectedly small for the most symmetric of the sunspots, thereby increasing our confidence in the inversion procedure and allowing a more meaningful comparison with magnetostatic models; (2) the inversion suggests that the magnetic field occupies significant fractions of the area in both light and dark penumbral filaments; (3) the intrinsic field does not fall below 600 G, either in the sunspot or in the surrounding plage areas, and is typically 700-800 G at the outer edge of the penumbra; (4) the radial variation of the vector field in these sunspots does not agree with "return flux" models (Flå, Osherovich, and Skumanich) - even at the outer edge of the penumbrae, the field remains inclined at an angle of 70° ; (5) the variation of the poloidal field strength and inclination with distance from the center of the symmetric sunspots exhibits little nonpotential character and is well represented by the potential field of a buried dipole; (6) significant azimuthal twist of the magnetic field is noted for one of our two isolated, symmetric sunspots; this twist appears to be real and is likely due to electric currents aligned with the poloidal (potential) field. We conclude that force-free photospheric fields are implied for those symmetric sunspots not exhibiting an azimuthal twist.