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arXiv · 2601.05321

The gravitational stratification of multifluid and multispecies plasma

F. Zhang·J. Martínez-Sykora·Q. M. Wargnier·V. H. Hansteen
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Abstract

Context. The solar atmosphere is gravitationally stratified and consists of several layers at temperatures that vary by several orders of magnitude. Consequently, the solar atmospheric plasma changes from weakly ionized in the photosphere, partially ionized in the chromosphere, and to fully ionized in the corona. However, integrating ionization and recombination processes into multifluid solar plasma models with gravitational stratification continues to be a nontrivial task. Aims. We intend to provide a method for constructing multifluid+multispecies (MFMS) gravitational stratification that satisfies the ionization equilibrium and hydrostatic equilibrium at the same time, avoiding causing nonphysical disturbances and numerical instability due to the initial imbalances. Methods. We assume that collisional interactions between fluids are sufficient for coupling all fluids when there is no high-frequency external driving force imposed. Ionization fractions can be (I) calculated assuming ionization in statistical equilibrium at any given temperature or (II) extracted from other atmospheric models. A simple numerical integration routine would then be used to construct MFMS gravitational stratifications. Results. The gravitational stratification in hydrostatic equilibrium can be constructed using the present numerical integration routine with any given ionization fractions of multispecies plasmas. Meanwhile, without any dynamic driving force, fluid decoupling is initiated, particularly in the transition region of the constructed stratification, while the total velocity of all fluids remains at the level of zero. Conclusions. A gravitational stratification constructed using the present routine can be used in MFMS models to study specific dynamics without being affected by the initial imbalances.

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F. Zhang, J. Martínez-Sykora, Q. M. Wargnier, V. H. Hansteen. 2026-01-08. The gravitational stratification of multifluid and multispecies plasma. https://arxiv.org/abs/2601.05321

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