Abstract
Abstract. This paper deals with nonsteady perturbations of the magnetosheath parameters which are related to variations of the interplanetary magnetic field from north to south under a constant solar wind dynamic pressure. The magnetic field changes its direction within a thin layer which is convected with the plasma from the bow shock to the ionopause. In the course of time, this current layer is amplified during its motion towards the magnetopause. The intensity of the current is increasing, the layer thickness is decreasing, and the gradients of parameters are becoming much sharper while the layer is approaching the magnetopause. The curvature radius of this layer is decreasing while it is draping around the magnetopause. This curved layer structure with reversed magnetic field in the magnetosheath is found to be unstable with respect to the interchange instability. The growth rate of the instability is obtained for different positions of the layer. Key words. Magnetospheric physics (magnetosheath)
Highlights
Solar wind conditions are very changeable, and in particular, the interplanetary magnetic field can reverse its direction
This paper deals with nonsteady perturbations of the magnetosheath parameters which are related to variations of the interplanetary magnetic field from north to south under a constant solar wind dynamic pressure
There are five main factors providing an enhancement of the interchange instability growth rate for the layer: 1) Increase in the thickness of the layer; 2) Increase in the magnetic field strength on the both sides of the layer; 3) Decrease in the plasma density; 4) Increase in the wave number; 5) Decrease in the local curvature radius of the layer
Summary
Solar wind conditions are very changeable, and in particular, the interplanetary magnetic field can reverse its direction. Tangential discontinuities carried by the solar wind are typical structures with such interplanetary magnetic field (IMF) variations. Horbury et al (2001) analyzed solar wind discontinuities using three spacecraft observations, and they identified about 14% of the observations as tangential discontinuities which are characterized by large variations of the total magnetic field with respect to its maximum value. The time scale of a tangential discontinuity estimated from the example of Horbury et al (2001) is less than 1 min. Thin current layers related to the tangential discontinuities are coming to the magnetosheath. They are moving towards the magnetopause, together with the ambient plasma. Approaching towards the magnetopause, these layers have a curvature radius being approximately equal to that of the magnetopause
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