INVESTIGATION OF MACROSCOPIC INSTABILITIES AT THE HELIOPAUSE BOUNDARY SURFACEстатья
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Дата последнего поиска статьи во внешних источниках: 27 мая 2015 г.
Аннотация:In many papers of the recent past stationary models for the plasma flow configuration in the interface region between the unperturbed interstellar plasma flow and the solar wind plasma flow have been presented and discussed. As a consequence of an MHD-type interaction of these flows a free pressure equilibrium surface, called the heliopause, is formed with a frontal nose part in the upwind direction and a tail region pointing into the downwind direction. It has, however, been left totally unclear in all of these models whether or not the derived stationary heliopause configurations are stable when subject to magnetohydrodynamical or hydrodynamical perturbations connected with time-dependent or turbulent structures in the counter-flowing plasmas. Therefore, we are studying here in detail the stability properties of the heliopause boundary surface with respect to perturbations of hydrodynamical type. As we show in this paper the problem of stability has a different quality in the nose region and in the off-nose region (the flanks of the heliopause). We are especially devoting our attention to these latter regions and investigate general forms of Kelvin-Helmholtz instabilities for the actually prevailing transition conditions there. It can be shown that, within a critical angle of perturbation wavevectors with respect to the local velocity vector at the heliopause, instability can always be expected with decreasing increments for a decreasing ratio of densities on the solar and on the interstellar side of the heliopause, respectively. Under the auspices of our theoretical results we are analysing possible consequences for the turbulent structure of the actual heliopause at different phases of the solar cycle. So we are describing observational effects of a turbulent plasma mixing in the region near the heliopause on the penetration of neutral hydrogen into the inner heliosphere. In addition the flow in the vicinity of the stagnation point is mathematically described by us, and the problem of stability of this type of flow is discussed.