Downflows in sunspot umbral dots

Abstract

We study the velocity field of umbral dots at a resolution of 0.14". Our analysis is based on full Stokes spectropolarimetric measurements of a pore taken with the CRISP instrument at the Swedish 1-m Solar Telescope. We determine the flow velocity at different heights in the photosphere from a bisector analysis of the Fe I 630 nm lines. In addtion, we use the observed Stokes Q, U, and V profiles to characterize the magnetic properties of these structures. We find that most umbral dots are associated with strong upflows in deep photospheric layers. Some of them also show concentrated patches of downflows at their edges, with sizes of about 0.25", velocities of up to 1000 m/s, and enhanced net circular polarization signals. The downflows evolve rapidly and have lifetimes of only a few minutes. These results appear to validate numerical models of magnetoconvection in the presence of strong magnetic fields.

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References in corpus (6)

• CRISP Spectropolarimetric Imaging of Penumbral Fine Structure
• Magneto-convection in a sunspot umbra
• Stokes imaging polarimetry using image restoration at the Swedish 1-m Solar Telescope
• Properties of simulated sunspot umbral dots
• The flow field in the sunspot canopy
• Spectropolarimetery of umbral fine structures from Hinode: Evidence for magnetoconvection

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