The velocity field of sunspot penumbrae II. Return flow and magnetic fields of opposite polarity

Aims. We search for penumbral magnetic fields of opposite polarity and for their correspondence with downflows. Methods. We used spectropolarimetric HINODE data of a spot very close to disk center to suppress the horizontal velocity components as much as possible. We focus our study on 3-lobe Stokes V profiles. Results. From forward modeling and inversions, we show that 3-lobe profiles testify to the presence of opposite magnetic fields. They occur predominately in the mid and outer penumbra and are associated with downflows in the deep layers of the photosphere. Conclusions. Standard magnetograms show that only 4% of the penumbral area harbors magnetic fields of opposite polarity. If 3-lobe profiles are included in the analysis, this number increases to 17%.