| Автор | Voigt, Gerd‐Hannes |
| Дата выпуска | 1986 |
| dc.description | Field‐aligned Birkeland currents and the twist of magnetic tail field lines are calculated for an axially symmetric pole‐on magnetosphere. The magnetic field components in the magnetospheric tail result from linear solutions to the MHD equilibrium problem. The field line twist angle, ε = arc tan (B<sub>ϕ</sub>/B<sub>z</sub>), is shown to be dependent on the radial distance measured from the tail axis, on the amount of thermal plasma confined in closed magnetotail flux tubes, and on the ionospheric Pedersen conductivity. The field lines are maximally twisted in the force‐free tail configurations; they are minimally twisted if the magnetotail reaches the state of maximum plasma pressure, the so‐called Harris sheet limit. The field line twist results from the planetary rotation, which leads to the development of a toroidal magnetic B<sub>ϕ</sub> component and to differentially rotating magnetic field lines. If centrifugal forces become important, the thermal plasma pressure P(A) in the Grad‐Shafranov equation assumes the form P(A, r) which allows centrifugal forces to be included in the MHD equilibrium formalism. The equilibrium model reveals that magnetopause field lines do not rotate because the magnetopause is held in place by the solar wind stream. For a given ionospheric conductivity and a given thermal plasma content within the tail, the field line helix is twisted most near the center of the circular tail plasma sheet. The field‐aligned Birkeland currents reach their maximum strength on tail field lines that confine the plasma sheet. Thus polar aurorae are expected to appear around both the dayside and nightside magnetic poles at latitudes where the plasma sheet field lines map into the planet's ionosphere. This theoretical model was originally developed for the anticipated pole‐on magnetosphere of Uranus. Thus references to the Uranian magnetosphere that appear in this study and in the quoted literature apply to hypotheses that had been developed before the closest approach of Voyager 2 at Uranus on January 24, 1986. However, the results of this study are sufficiently general to allow their application to other rotating axially symmetric plasma‐magnetic field configurations in space. |
| Формат | application.pdf |
| Копирайт | Copyright 1986 by the American Geophysical Union. |
| Тема | MAGNETOSPHERIC PHYSICS |
| Тема | Magnetospheric configuration and dynamics |
| Тема | Planetary magnetospheres |
| Тема | PLANETARY SCIENCES: SOLID SURFACE PLANETS |
| Тема | Magnetospheres |
| Тема | PLANETARY SCIENCES: FLUID PLANETS |
| Тема | Magnetospheres |
| Тема | PLANETARY SCIENCES: COMETS AND SMALL BODIES |
| Тема | Magnetospheres |
| Тема | SPACE PLASMA PHYSICS |
| Тема | Kinetic and MHD theory |
| Название | Field line twist and field‐aligned currents in an axially symmetric equilibrium magnetosphere |
| Тип | article |
| DOI | 10.1029/JA091iA10p10995 |
| Electronic ISSN | 2156-2202 |
| Print ISSN | 0148-0227 |
| Журнал | Journal of Geophysical Research: Space Physics |
| Том | 91 |
| Первая страница | 10995 |
| Последняя страница | 11002 |
| Выпуск | A10 |
| Библиографическая ссылка | Abramowitz, M., and I. A.Stegun, Handbook of Mathematical Functions, Dover, New York, 1965. |
| Библиографическая ссылка | Bateman, G., MHD Instabilities, 66–68, MIT Press, Cambridge, Mass., 1980. |
| Библиографическая ссылка | Cheng, A. F., Magnetosphere, rings, and moons of Uranus, Uranus and Neptune, NASA Conf Publ. NASA CP‐2330, 541–556, 1984. |
| Библиографическая ссылка | Erickson, G. M., On the cause of X‐line formation in the near‐earth plasma sheet: Results of adiabatic convection of plasma sheet plasma, Magnetic Reconnection, Geophys. Monogr. Ser., 30Hones, E. W., 296–302, AGU, Washington, D.C., 1984. |
| Библиографическая ссылка | Hill, T. W., Rotationally induced Birkeland current systems, Magnetospheric Currents, Geophys. Monogr. Ser., 28Potemra, A., 340–349, AGU, Washington, D.C., 1983. |
| Библиографическая ссылка | Hill, T. W., and A. J.Dessler, Twisting of planetary magnetotailsChapman Conference on Magnetotail PhysicsLaurel, Md.Oct. 28–31, 1985. |
| Библиографическая ссылка | Hill, T. W., A. J.Dessler, and M. E.Rassbach, Aurora on Uranus: A Faraday disk dynamo mechanism, Planet. Space Sci., 31, 1187–1198, 1983. |
| Библиографическая ссылка | Ip, A. K., and G.‐H.Voigt, Plasma‐dominated magnetic field configurations for the magnetosphere of Uranus, J. Geophys. Res., 90, 6287–6293, 1985. |
| Библиографическая ссылка | Schindler, K., and J.Birn, Self‐consistent theory of time‐dependent convection in the earth's magnetotail, J. Geophys. Res., 87, 2263–2275, 1982. |
| Библиографическая ссылка | Voigt, G.‐H., Magnetospheric equilibrium configurations and slow adiabatic convection, Proceedings of the Chapman Conference on Solar Wind‐Magnetosphere CouplingKamide, Y., and J.Slavin, 233–274, Terra/Reidel, Tokyo, 1986. |
| Библиографическая ссылка | Voigt, G.‐H., T. W.Hill, and A. J.Dessler, The magnetosphere of Uranus: Plasma sources, convection and field configuration, Astrophys. J., 266, 390–401, 1983. |
| Библиографическая ссылка | Wolf, R. A., The quasi‐static (slow‐flow) region of the magnetosphere, Solar Terrestrial PhysicsCarovillano, R. L., and J. M.Forbes, 303–368, D. Reidel, Hingham, Mass., 1983. |
| Библиографическая ссылка | Yates, G. K., and M.Heinemann, Three‐dimensional axisymmetric magnetosphere in pressure balance with the solar wind, J. Geophys. Res., 6777–6790, 1986. |
