UNCOMBED FIELDS AS THE SOURCE OF THE BROAD-BAND CIRCULAR-POLARIZATIONOF SUNSPOTS

We investigate the production of broad-band circular polarization (BBC ) of sunspots using a model inspired by the discovery of small-scale v ariations of magnetic inclination in sunspot penumbrae. The proposed m odel is a simple representation of a horizontal magnetic flux tube emb edded in an inclined magnetic field, with a flow in either one or both components (Evershed flow). This model is shown to produce a sizeable BBC without requiring substantial net vertical gradients of the magne tic vector. It reproduces the BBC observations in a qualitatively corr ect and quantitatively acceptable manner for reasonable values of its free parameters. In addition, our model also explains the crossover ef fect observed in sunspot penumbrae. The fits to the observations suppo rt the presence of a larger velocity in the horizontal magnetic filame nts than in the inclined field. We point out that the BBC is complemen tary to high resolution images in that it diagnoses the height variati on of the small-scale structure of sunspot magnetic fields. By combini ng the results from both techniques we outline the 3-D fine-scale stru cture of the magnetic field in the photospheric layers of sunspot penu mbrae. The most important result is that the two differently inclined components of the field do not simply form vertical sheets, but rather must have a horizontal interface near the level of line formation.