Journal
ASTROPHYSICAL JOURNAL
Volume 789, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/789/2/132
Keywords
convection; dynamo; magnetohydrodynamics (MHD); radiative transfer; Sun: magnetic fields; Sun: photosphere
Categories
Funding
- National Science Foundation [NHAO0002]
- NASA High-End Computing (HEC) Program through the NASA Advanced Super-computing (NAS) Division at Ames Research Center [s9025]
- University of Tennessee through the use of the Kraken computing resource at the National Institute for Computational Sciences [AST100005]
- NASA [NNH09AK02I, NNH12CF68C, NNX12AB35G]
- STFC [ST/H000429/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/H000429/1] Funding Source: researchfish
- NASA [30910, NNX12AB35G] Funding Source: Federal RePORTER
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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 tau = 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 tau = 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 tau = 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.
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