Observation of Penumbra Downflows

Abstract

This paper describes penumbra supersonic downflows (PSDs), which can be observed using the Hinode spectropolarimeter. The map obtained from red wing wavelengths at the half of line depth of the Fe I λ 6302 Å line makes it easy to detect these flows. They represent visible fragments of penumbral filaments as they turn sharply before entering the deep layers at the junction of the penumbra and the undisturbed photosphere. The PSD regions observed in this way are a part of the penumbral region where magnetic field lines bend relative to the plane parallel to the spectrometer’s aperture and experience polarity reversal of the longitudinal field. The polarity reversal zone is clearly visible on the map constructed from the values of signed net circular polarization (sNCP), i.e., the NCP values multiplied by the sign of the field. The region where the sNCP changes sign is characterized by elevated values of line-of-sight velocities, measured from the center of gravity of the circular polarization absolute value. In most cases, PSDs are observed on the limb side of the penumbra. On the side of the solar disk center, PSDs can be detected by other means, in particular, a map can be constructed from the positions of the centers of gravity of the red lobe in the linear polarization profile. Such a map also clearly shows the moat flow region.