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

TL;DR

This study investigates the presence of opposite polarity magnetic fields and downflows in sunspot penumbrae using spectropolarimetric data, revealing a higher prevalence of such fields when including 3-lobe Stokes V profiles.

Contribution

It demonstrates that 3-lobe Stokes V profiles are indicative of opposite magnetic fields and downflows, increasing the detected opposite polarity area in penumbrae.

Findings

Opposite polarity fields are mainly in mid and outer penumbra.

Including 3-lobe profiles raises the opposite polarity area from 4% to 17%.

Opposite polarity fields are associated with deep-layer downflows.

Abstract

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%.