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American Astronomical Society, Astrophysical Journal, 2(680), p. L145-L148, 2008

DOI: 10.1086/589569

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Heliosphere Termination Shock as a Transformer of Magnetic Field from Lognormal to Normal Distribution

Journal article published in 2008 by M. Q. Chen, J. K. Chao, L. C. Lee ORCID, and N. H. Ting
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

A mechanism is proposed to demonstrate that the strength of magnetic field can be transformed from a lognormal to a normal distribution as the solar wind passes through the heliosphere termination shock (TS), which explains the recent Voyager 1 observations. The TS is approximated as a perpendicular MHD shock. Synthetic simulations using random picks of 3 × 107 upstream states generate the downstream magnetic field based on the Rankine-Hugoniot relation across the TS. Thus, it is implicitly implied that the magnetic fluctuations are parallel to the shock surface. A lognormal distribution is transformed to a normal distribution for small plasma beta (β10 = 0.1), but for larger beta (β10 = 10), the distribution of B2 remains a lognormal. The observation of a normal magnetic field distribution downstream of the TS provides an upper bound (β10 < 1) for the solar wind beta near the TS, which in turn provides an upper bound for the number density of interstellar neutral hydrogens. One of the TS crossings from the Voyager 2 magnetic field and plasma observations on 2007 September 1 was found to have reformation of the local structure when the upstream beta, β10, without including pickup protons equals 0.04, which is a low-beta supercritical quasi-perpendicular shock.