التفاصيل البيبلوغرافية
| العنوان: |
Equilibrium Kinetic Theory of Weakly Anisotropic Embedded Thin Current Sheets. |
| المؤلفون: |
Sitnov, M. I., Arnold, H. |
| المصدر: |
Journal of Geophysical Research. Space Physics; Nov2022, Vol. 127 Issue 11, p1-19, 19p |
| مصطلحات موضوعية: |
CURRENT sheets, EARTH currents, PLASMA turbulence, MAGNETIC fields, DENSITY currents, PLASMA density |
| مستخلص: |
Statistical and case studies, as well as data‐mining reconstructions suggest that the magnetotail current in the substorm growth phase has a multiscale structure with a thin ion‐scale current sheet embedded into a much thicker sheet. This multiscale structure may be critically important for the tail stability and onset conditions for magnetospheric substorms. The observed thin current sheets are found to be too long to be explained by the models with isotropic plasmas. At the same time, plasma observations reveal only weak field‐aligned anisotropy of the ion species, whereas the anisotropic electron contribution is insufficient to explain the force balance discrepancy. Here we elaborate a self‐consistent equilibrium theory of multiscale current sheets, which differs from conventional isotropic models by weak ion anisotropy outside the sheet and agyrotropy caused by quasi‐adiabatic ion orbits inside the sheet. It is shown that, in spite of weak anisotropy, the current density perturbation may be quite strong and localized on the scale of the figure‐of‐eight ion orbits. The magnetic field, current and plasma density in the limit of weak field‐aligned ion anisotropy and strong current sheet embedding, when the ion scale thin current sheet is nested in a much thicker Harris‐like current sheet, are investigated and presented in an analytical form making it possible to describe the multiscale equilibrium in sharply stretched 2D magnetic field configurations and to use it in kinetic simulations and stability analysis. Plain Language Summary: Conventional kinetic equilibria with isotropic pressures for ions and electrons aimed to describe the current sheet in Earth's magnetotail cannot reproduce its multiscale structure with the proton gyroradius‐scale current sheet being embedded into a much thicker sheet. They cannot explain either the formation of such thin current sheets sufficiently far from Earth. The embedding effect can be reproduced in case of anisotropic and agyrotropic plasmas because orbits of weakly magnetized ions near the current sheet deviate from the Larmor circle and become more like a figure of eight. However, the corresponding multiscale current sheet models have been studied so far for substantial and strong plasma anisotropy, while observations suggest that the tail plasmas are weakly anisotropic. Here we perform an analysis of a weakly anisotropic current sheet model, which transforms in the isotropic limit into a classical Harris sheet model, and show that the key observed embedding features can be reproduced. Key Points: Kinetic equilibria of ion‐scale current sheets embedded into a thicker weakly anisotropic Harris‐like current sheet are investigatedThe current density increase due to quasi‐adiabatic ion motions may be substantial in spite of weak plasma anisotropy2D thin current sheets have aspect ratios consistent with observations and controlled by the embedding strength [ABSTRACT FROM AUTHOR] |
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| قاعدة البيانات: |
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