Striation and convection in penumbral filaments

Abstract

Observations with the 1-m Swedish Solar Telescope of the flows seen in penumbral filaments are presented. Time sequences of bright filaments show overturning motions strikingly similar to those seen along the walls of small isolated structures in the active regions. The filaments show outward propagating striations with inclination angles suggesting that they are aligned with the local magnetic field. We interpret it as the equivalent of the striations seen in the walls of small isolated magnetic structures. Their origin is then a corrugation of the boundary between an overturning convective flow inside the filament and the magnetic field wrapping around it. The outward propagation is a combination of a pattern motion due to the downflow observed along the sides of bright filaments, and the Evershed flow. The observed short wavelength of the striation argues against the existence of a dynamically significant horizontal field inside the bright filaments. Its intensity contrast is explained by the same physical effect that causes the dark cores of filaments, light bridges and `canals'. In this way striation represents an important clue to the physics of penumbral structure and its relation with other magnetic structures on the solar surface. We put this in perspective with results from the recent 3-D radiative hydrodynamic simulations.

Accepted for publication in A&A

References in corpus (9)

• Magneto-convection in a sunspot umbra
• MHD simulations of penumbra fine structure
• Magnetostatic penumbra models with field-free gaps
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• Deep probing of the photospheric sunspot penumbra: no evidence for magnetic field-free gaps
• Active region fine structure observed at 0.08 arcsec resolution
• Striation and convection in penumbral filaments
• Lateral downflows in sunspot penumbral filaments and their temporal evolution
• SST/CRISP Observations of Convective Flows in a Sunspot Penumbra
• Insight into the solar plage chromosphere with DKIST
• Multi-frame blind deconvolution and phase diversity with statistical inclusion of uncorrected high-order modes