On accelerated magnetosheath flows under northward IMF

Тип публикации: статья из журнала

Год издания: 2011

Идентификатор DOI: 10.1029/2010GL045998

Ключевые слова: Mach number, Magnetic fields, Magnetosphere, Solar wind, Accelerated flows, Earth radii, Magnetic field line, Magnetic reconnections, Magnetosheath flow, Magnetosheath plasma, Magnetosheaths, Maximum speed, Northward IMF, Physical mechanism, Semi-analytical, Solar wind speed, Solar wind velocity, Tension force, Total pressure, Typical values, Pressure gradient, acceleration, force, magnetic field, magnetosphere, pressure gradient, solar wind, wind velocity

Аннотация: We study the acceleration of magnetosheath plasma using a semi-analytical magnetic string approach for a range of solar wind Alfven Mach numbers, M-A, between 2 and 20. We work with an IMF vector perpendicular to the solar wind velocity, V-sw, and pointing north. We do not invoke magnetic reconnection. Our results indicate that magnetosheath speeds can exceed the solar wind speed, and the ratio V/V-sw increases with decreasing M-A. Analyzing the dependence of this ratio on M-A, we find that for M-A = 2, maximum V/V-sw approximate to 1.6, and for M-A = 10-20, maximum V/V-sw varies from 1.21 to 1.13. Maximum speeds occur a few Earth radii (R-E) tailward of the dawn-dusk terminator. The thickness of the accelerated flow layer varies as M-A(-2). Taking the magnetopause subsolar distance as 10 R-E, we find typical values for the thickness of similar to 4 R-E for M-A = 3 and 0.35 R-E for M-A = 10. The physical mechanism is that of draping of the magnetic field lines around the magnetosphere, and the associated magnetic tension and total pressure gradient forces acting on the flow. For lower M-A the plasma depletion is stronger, and thus the acceleration produced by the pressure gradient is larger. An additional acceleration is produced by the magnetic tension, which is stronger for smaller M-A. At the dayside the pressure gradient and magnetic tension forces both act in the same direction. But tailward of the terminator the magnetic tension starts to act in the opposite direction to the pressure gradient. When the resulting force vanishes, the highest speed is attained. Citation: Erkaev, N. V., C. J. Farrugia, B. Harris, and H. K. Biernat (2011), On accelerated magnetosheath flows under northward IMF, Geophys. Res. Lett., 38, L01104, doi: 10.1029/2010GL045998.

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Издание

Журнал: GEOPHYSICAL RESEARCH LETTERS

Выпуск журнала: Vol. 38

ISSN журнала: 00948276

Место издания: WASHINGTON

Издатель: AMER GEOPHYSICAL UNION

Авторы

  • Erkaev N.V. (Siberian Federal University)
  • Farrugia C.J. (Department of Physics,University of New Hampshire)
  • Harris B. (Space Science Center,University of New Hampshire)
  • Biernat H.K. (Institute for Theoretical Physics,University of Graz)

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