Non-steady-state solar wind-magnetosphere interaction
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Most of the theories proposed to explain the interaction between the solar wind and the geomagnetic field are stationary descriptions based on ideal MHD. In this review an alternative, nonstationary description is discussed. According to this description, most of the plasma-field irregularities, i.e., plasmoids, detected in the solar wind can penetrate inside the geomagnetic field beyond what is considered to be the mean position of the magnetopause. It is the patchy solar wind plasma impinging on the geomagnetic field which imposes rapidly changing and non-uniform boundary conditions over the whole outer magnetospheric surface. This contrasts with the general belief that the observed field variations or 'events' arise sporadically near the magnetopause as the result of some plasma instability. A brief historical review is given to illustrate the evolution of the theoretical models proposed to explain the interaction of the solar wind with the magnetosphere. The emergence of the idea of 'impulsive penetration' of solar wind plasma irregularities into the magnetosphere is emphasized especially. A kinetic model of the unperturbed magnetopause is described. This model corresponds to a closed magnetosphere whose surface is a tangential discontinuity. This transition layer can sustain plasma jettings and can be traversed by impulsive penetrating plasmoids. This is against the general belief which considers tangential discontinuities as the worse case with respect to impulsive penetration and plasma jettings. The mean features of the theory of impulsive penetration are presented. Gusty penetration of solar wind plasmoids depends on their excess momentum density and on the orientation of the IMF. The motion of plasmoids across non-uniform magnetic field configurations (tangential discontinuities) is discussed theoretically. When the dielectric constant of the streaming plasma is large enough for collective polarization effects to become important, an electric field develops which permits cross-B motions of all charged particles as a whole plasma entity. It is re-emphasized that the value of the integrated Pedersen conductivity is a determining factor in cross-B plasma motion. On the other hand, interconnection of interplanetary magnetic field lines and geomagnetic field lines results from collective diamagnetic effects produced by magnetized plasmoids injected into the magnetosphere. Several consequences of this penetration mechanism are discussed. These are: the escape of energetic particles out of the magnetosphere, the eastward deflection of penetrating plasmoids, the magnetospheric and ionospheric convection patterns, the erosion of plasmoids, and the mass/momentum loading effects. Some significant experimental geophysical observations supporting the impulsive penetration model are also discussed.
CitationLemaire, J.; Roth, M. (1991). Non-steady-state solar wind-magnetosphere interaction. , Space Science Reviews, Vol. 57, Issue 1-2, 59-108, DOI: 10.1007/BF00195951.