2006/09/06 by G. B. Scharmer, H. C. Spruit · 12 citations
Physics and Astronomy · #Astrophysical Phenomena and Observations #Field (mathematics) #Field strength #Ionosphere and magnetosphere dynamics #Magnetic field #Magnetohydrodynamics #Penumbra #Solar and Space Plasma Dynamics #Sunspot #astro-ph
paper · pdf · doi:10.1051/0004-6361:20066019
accepted for publication in A&A
arxiv created 2006/09/06 · openalex publication_date 2006/09/12 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present numerical 2D magnetostatic models for sunspot penumbrae consisting of radially aligned field-free gaps in a potential magnetic field, as proposed by Spruit & Scharmer (2006, A&A, 447, 343). The shape of the gaps and the field configurations around them are computed consistently from the condition of magnetostatic pressure balance between the gap and the magnetic field. The results show that field-free gaps in the inner penumbra are cusp-shaped and bounded by a magnetic field inclined by about from the vertical. Here, the magnetic component has a Wilson depression on the order 200–300 km relative to the top of the field-free gap; the gaps should thus appear as noticeably elevated features. This structure explains the large variations in field strength in the inner penumbra inferred from magnetograms and two-component inversions, and the varying appearance of the inner penumbra with viewing angle. In the outer penumbra, on the other hand, the gaps are flat-topped with a horizontal magnetic field above the middle of the gap. The magnetic field has large inclination variations horizontally, but only small fluctuations in field strength, in agreement with observations.