http://arxiv.org/abs/1907.06476
In an observation review published in Solar Physics in 2018, H. Balthasar shows that observations with different telescopes, spectral lines and interpretation methods all agree about a vertical magnetic field gradient in solar active regions on the order of 3 G/km, when the horizontal magnetic field gradient is found of 0.3 G/km only. This represents an inexplicable discrepancy with respect to the divB=0 law. The objective of this paper is to explain these observations through the law B=\mu_0(H+M) in magnetised media. Magnetisation is due to the plasma diamagnetism, which results from the spiral motion of free electrons or charges about the magnetic field. Their usual photospheric densities lead to very weak magnetisation M, four orders of magnitude smaller than H. It is then assumed that electrons escape from the solar interior, where their thermal velocity is much larger than the escape velocity, and accumulate in the photosphere where they are slowed down by the charge-dipole interaction with the neutral Hydrogen atoms. By evaluating the magnetic energy of the microscopic atom embedded in the magnetised medium obeying the macroscopic law B=\mu_0(H+M), it is shown that the Zeeman hamiltonian is due to the effect of H. Thus, what is measured is H. The decrease of the density with height is responsible for non-zero divergence of M, which is compensated for by the divergence of H, in order to ensure divB=0. The behavior of the observed quantities is recovered. The problem of the divergence of the observed magnetic field in solar active regions finally reveals evidence of electron accumulation in the solar photosphere. This is not the case of the heavier protons, which remain in lower layers. Electric field would thus be present in the solar interior, but as the total charge remains negligible, no electric field or effect would result outside the star.
V. Bommier
Tue, 16 Jul 19
86/89
Comments: 10 pages, 2 figures, submitted to Astronomy and Astrophysics, Section Astrophysical Processes (in revision)
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