NUMERICAL SIMULATIONS OF QUIET SUN MAGNETISM: ON THE CONTRIBUTION FROM A SMALL-SCALE DYNAMO

By Matthias Rempel. 2014

162 citations recorded by the source corpus.

We present a series of radiative MHD simulations addressing the origin and distribution of the mixed polarity magnetic field in the solar photosphere. To this end, we consider numerical simulations that cover the uppermost 2–6 Mm of the solar convection zone and we explore scales ranging from 2 km to 25 Mm. We study how the strength and distribution of the magnetic field in the photosphere and subsurface layers depend on resolution, domain size, and boundary conditions. We find that 50% of the magnetic energy at the τ = 1 level comes from fields with the less than 500 G strength and that 50% of the energy resides on scales smaller than about 100 km. While the probability distribution functions are essentially independent of resolution, properly describing the spectral energy distribution requires grid spacings of 8 km or smaller. The formation of flux concentrations in the photosphere exceeding 1 kG requires a mean vertical field strength greater than 30–40 G at τ = 1. The filling factor of kG flux concentrations increases with overall domain size as the magnetic field becomes organized by larger, longer-lived flow structures. A solution with a mean vertical field strength of around 85 G at τ = 1 requires a subsurface rms field strength increasing with depth at the same rate as the equipartition field strength. We consider this an upper limit for the quiet Sun field strength, which implies that most of the convection zone is magnetized close to the equipartition. We discuss these findings in view of recent high-resolution spectropolarimetric observations of quiet Sun magnetism.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/d868728e357a4d352c936b32f912c4c94485a619

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In Astronomy and Astrophysics

1. Laurent Gizon
2. B. Vršnak
3. W. Manchester IV
4. L. Green
5. Tibor Török
6. S. Solanki
7. Astrid Veronig
8. R. Marsden

Citations in the corpus

• EXTENSION OF THE MURAM RADIATIVE MHD CODE FOR CORONAL SIMULATIONS (2016, methodology): “The bottom boundary conditions are similar to those discussed in Rempel (2014).”
• The Solar Orbiter mission (2020, background): “Magnetohydrodynamics simulations indicate a local turbulent dynamo in the Sun’s convection zone (Brun et al. 2004; Strugarek et al. 2016; Whitbread et al. 2019) and even in the nearsurface layers (Vögler & Schüssler 2007b; Rempel 2014).”
• The Origin, Early Evolution and Predictability of Solar Eruptions (2018, background): “Work in this vein began with quiet sun magneto-convection (e.g. Stein and Nordlund, 2006; Abbett, 2007; Rempel, 2014), which shows the development of a near-surface dynamo and formation of kiloGauss flux tubes in convective downdrafts.”
• The Polarimetric and Helioseismic Imager on Solar Orbiter (2019, background): “In addition to the cancellation effects just mentioned, MHD simulations indicate that a small-scale turbulent dynamo is acting in the solar interior and at its surface (Brun et al. 2004; Vögler & Schüssler 2007; Rempel 2014).”