Uncombed fields as the source of the broad-band circular polarization of sunspots

We investigate the production of broad-band circular polarization (BBC) of sunspots using a model inspired by the discovery of small-scale variations of magnetic inclination in sunspot penumbrae. The proposed model is a simple representation of a horizontal magnetic flux tube embedded 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 magnetic vector. It reproduces the BBC observations in a qualitatively correct and quantitatively acceptable manner for reasonable values of its free parameters. In addition, our model also explains the crossover effect observed in sunspot penumbrae