Control of impulsive penetration of solar wind irregularities into the magnetosphere by the interplanetary magnetic field direction
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Impulsive penetration of a solar wind filament into the magnetosphere is possible when the plasma element has an excess momentum density with respect to the background medium. This first condition is satisfied when the density is larger inside than outside the plasma inhomogeneity. In this paper we discuss the second condition which must be satisfied for such a plasma element to be captured by the magnetosphere: the magnetization vector (M) carried by this plasma must have a positive component along the direction of B0, the magnetic field where the element penetrates through the magnetopause. On the contrary, when M · B0 < 0, the filament is stopped at the surface of the magnetopause. Thus the outcome of the interaction of the filament with the magnetosphere depends upon the orientation of the Interplanetary Magnetic Field. For instance, penetration and capture in the frontside magnetosphere implies that Bsw, the Interplanetary Magnetic Field, has a southward, or a small northward, component. Penetration and capture in the northern lobe of the magnetotail is favoured for an IMF pointing away from the Sun; in the southern lobe Bsw must be directed towards the Sun for capture. Finally, for capture in the vicinity of the polar cusps the magnetospheric field (B0) assumes a wider range of orientations. Therefore, near the neutral points, it is easier to find a place where the condition M · B0 > 0 is satisfied than elsewhere. As a consequence, the penetration and capture of solar wind irregularities in the cleft regions is possible for almost any orientation of the interplanetary magnetic field direction. All observations made to date support these theoretical conclusions.
CitationLemaire, J.; Rycroft, M.J.; Roth, M. (1979). Control of impulsive penetration of solar wind irregularities into the magnetosphere by the interplanetary magnetic field direction. , Planetary and Space Science, Vol. 27, Issue 1, 47-57, DOI: 10.1016/0032-0633(79)90146-6.