The continuum intensity as a function of magnetic field II. Local magnetic flux and convective flows

Abstract

To deepen our understanding of the role of small-scale magnetic fields in active regions (ARs) and in the quiet Sun (QS) on the solar irradiance, it is fundamental to investigate the physical processes underlying their continuum brightness. Previous results showed that magnetic elements in the QS reach larger continuum intensities than in ARs at disk center, but left this difference unexplained. We use Hinode/SP disk center data to study the influence of the local amount of magnetic flux on the vigour of the convective flows and the continuum intensity contrasts. The apparent (i.e. averaged over a pixel) longitudinal field strength and line-of-sight (LOS) plasma velocity were retrieved by means of Milne-Eddington inversions (VFISV code). We analyzed a series of boxes taken over AR plages and the QS, to determine how the continuum intensity contrast of magnetic elements, the amplitude of the vertical flows and the box-averaged contrast were affected by the mean longitudinal field strength in the box (which scales with the total unsigned flux in the box). Our results suggest that as the magnetic flux increases locally (e.g. from weak network to strong plage), the heating of the magnetic elements is reduced by the intermediate of a more suppressed convective energy transport within the larger and stronger magnetic patches. This, together with the known presence of larger magnetic features, could explain the previously found lower contrasts of the brightest magnetic elements in ARs compared to the QS. The inhibition of convection also affects the average continuum brightness of a photospheric region, so that at disk center, an area of photosphere in strong network or plage appears darker than a purely quiet one. This is qualitatively consistent with the predictions of 3D MHD simulations.

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Cited by in corpus (14)

• Properties of solar plage from a spatially coupled inversion of Hinode SP data
• Comparison of solar photospheric bright points between SUNRISE observations and MHD simulations
• Spectral variability of photospheric radiation due to faculae I: The Sun and Sun-like stars
• Comparison of physical properties of quiet and active regions through the analysis of MHD simulations of the solar photosphere
• Photometric Properties of Network and Faculae Derived from HMI Data Compensated for Scattered-Light
• Statistical evolution of quiet-Sun small scale magnetic features using Sunrise observations
• A comparison between solar plage and network properties
• Evolution and wave-like properties of the average solar supergranule
• Intensity contrast of solar plage as a function of magnetic flux at high spatial resolution
• The dark side of solar photospheric G-band bright points
• Intensity contrast of solar network and faculae -- II. Implications for solar irradiance modelling
• Brightness of the Sun's small scale magnetic field: proximity effects
• Analysis and modeling of solar irradiance variations
• A High-resolution, Inversion-Based Synoptic Study of Solar Granulation