MODELING THE SUN'S SMALL-SCALE GLOBAL PHOTOSPHERIC MAGNETIC FIELD

• Published in: The Astrophysical journal Vol. 830; no. 2; pp. 160 - 172
• Main Authors: Meyer, K. A., Mackay, D. H.
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 20.10.2016; IOP Publishing
• Subjects: Astrophysics; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Computer simulation; Corona; Coronal magnetic fields; COSMIC RADIATION; COSMIC RAY FLUX; Cosmic rays; DISTRIBUTION; Flow pattern; Fluctuations; HELIOSPHERE; Interplanetary magnetic field; INTERPLANETARY MAGNETIC FIELDS; Magnetic fields; MAGNETIC FLUX; Magnetism; MEAN-FIELD THEORY; PHOTOSPHERE; Photospheric magnetic fields; Photospheric magnetic flux; Quiet Sun; SIMULATION; Solar magnetic field; Solar surface; STEADY-STATE CONDITIONS; SUN; Sun: activity; Sun: corona; Sun: magnetic fields; Sun: photosphere; SURFACES
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/0004-637X/830/2/160

ABSTRACT We present a new model for the Sun's global photospheric magnetic field during a deep minimum of activity, in which no active regions emerge. The emergence and subsequent evolution of small-scale magnetic features across the full solar surface is simulated, subject to the influence of a global supergranular flow pattern. Visually, the resulting simulated magnetograms reproduce the typical structure and scale observed in quiet Sun magnetograms. Quantitatively, the simulation quickly reaches a steady state, resulting in a mean field and flux distribution that are in good agreement with those determined from observations. A potential coronal magnetic field is extrapolated from the simulated full Sun magnetograms to consider the implications of such a quiet photospheric magnetic field on the corona and inner heliosphere. The bulk of the coronal magnetic field closes very low down, in short connections between small-scale features in the simulated magnetic network. Just 0.1% of the photospheric magnetic flux is found to be open at 2.5 R , around 10-100 times less than that determined for typical Helioseismic and Magnetic Imager synoptic map observations. If such conditions were to exist on the Sun, this would lead to a significantly weaker interplanetary magnetic field than is currently observed, and hence a much higher cosmic ray flux at Earth.