Temporal evolution of the Evershed flow in sunspots. II. Physical properties and nature of Evershed clouds

Abstract

Context: Evershed clouds (ECs) represent the most conspicuous variation of the Evershed flow in sunspot penumbrae. Aims: We determine the physical properties of ECs from high spatial and temporal resolution spectropolarimetric measurements. Methods: The Stokes profiles of four visible and three infrared spectral lines are subject to inversions based on simple one-component models as well as more sophisticated realizations of penumbral flux tubes embedded in a static ambient field (uncombed models). Results: According to the one-component inversions, the EC phenomenon can be understood as a perturbation of the magnetic and dynamic configuration of the penumbral filaments along which these structures move. The uncombed inversions, on the other hand, suggest that ECs are the result of enhancements in the visibility of penumbral flux tubes. We conjecture that the enhancements are caused by a perturbation of the thermodynamic properties of the tubes, rather than by changes in the vector magnetic field. The feasibility of this mechanism is investigated performing numerical experiments of thick penumbral tubes in mechanical equilibrium with a background field. Conclusions: While the one-component inversions confirm many of the properties indicated by a simple line parameter analysis (Paper I of this series), we tend to give more credit to the results of the uncombed inversions because they take into account, at least in an approximate manner, the fine structure of the penumbra.

Accepted for publication in A&A

References in corpus (5)

• On the fine structure of the sunspot penumbrae. II. The nature of the Evershed flow
• On the fine structure of the sunspot penumbrae. III The vertical extension of penumbral filaments
• Temporal evolution of the Evershed flow in sunspots. I. Observational characterization of Evershed clouds
• The flow field in the sunspot canopy
• The structure of sunspot penumbrae IV. MHS equilibrium for penumbral flux tubes and the origin of dark core penumbral filaments and penumbral grains

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• Are there field-free gaps near tau=1 in sunspot penumbrae?
• Analysis of a Fragmenting Sunspot using Hinode Observations
• Models and Observations of Sunspot Penumbrae
• On spectropolarimetric measurements with visible lines
• Disintegration of Magnetic Flux in Decaying Sunspots as Observed with the Hinode SOT
• Three-lobed near-infrared Stokes V profiles in the quiet Sun
• Expulsion of counter Evershed flows from sunspot penumbrae
• The role of the Lorentz force in sunspot equilibrium
• The association between sunspot magnetic fields and superpenumbral fibrils