ON THE MAGNETIC AND VELOCITY-FIELD GEOMETRY OF SIMPLE SUNSPOTS

We have observed the disk passage of relatively simple round sunspots using a narrow-band filter and a large format CCD detector and have created magnetograms, Dopplergrams, and continuum images nearly simultaneously. The spectral resolution of the filter (88,000) allows the construction of ''spectra'' for all points in the field of view. The changing patterns of the line-of-sight magnetic fields with position around the spots and with position of spots on the solar disk show that the mean inclination of the magnetic field increases from 45-degrees-50-degrees to 70-degrees-75-degrees across the penumbra and that there is a fluctuation about the mean of about +/- 18-degrees. These inclination changes occur on the scale of the penumbral fibrils. In addition the direction changes are large enough that a substantial fraction of the magnetic field is horizontal (parallel to the solar surface) from the mid to outer penumbra. Our Doppler data show that the Evershed flow tends to occur in the regions where the magnetic field is horizontal. Taken together these observations suggest that the Evershed flow is confined to the regions of horizontal fields, which resolves the old difficulty of nonparallelism of magnetic and flow fields in a sunspot. We show that a simple sunspot model with azimuthal variations in inclination, but no azimuthal variations of field strength, is free from azimuthal Lorentz forces. The meridional currents which arises from the inclination variations are parallel to the field lines. This suggests that a cylindrically symmetric magnetostatic sunspot model can be perturbed into one with azimuthal variations in inclination with some adjustment in the meridional force balance.