On the predominance of oblique disturbances in the supersonic shear flow instability of the geomagnetic tail boundary

Abstract

Abstract.A study is made of the influence of the longitudinal magnetic field and density inhomogeneity on the supersonic shear flow instability at the magnetospheric tail boundary. It is shown that the most unstable are slow oblique (3D) disturbances, with a phase velocity approaching at a sufficiently large angle (with respect to the flow direction) the magnetosonic velocity. Their growth rate and spectral width are much larger than those of the usually considered longitudinal (2D) supersonic disturbances. The magnetic field reduces the compressibility effect and, unlike the subsonic case, has a noticeable destabilizing effect on the excitation of oblique disturbances.

The effect of transition layer inhomogeneity on the stability of compressible MHD fluids

“…It is known that the density and the magnetic field in the transition layer vary in the normal direction of TD. These variations cause the current convective (CC) instability [22]. In this case, the density variations lead to an instability and the magnetic field plays stabilizing role similar to the KH instability.…”

“…Moreover, it must be taken into account that these parameters usually have continuous variations across a surface with TD. On the other hand, it is clear that the presence of an inhomogeneity in the density or the magnetic field causes the interchange instability and this instability affects the surface wave stability which has been investigated recently [16][17][18][19][20][21][22][23]. In the short wavelength limit (the wavelength is smaller than the characteristic length of the inhomogeneity or transition layer) [16], the surface wave propagation is similar to that of inhomogeneous media with corresponding parameters.…”

“…In compressible fluids, by using linear and nonlinear methods [16][17][18][19], the dispersion relation of the surface wave is obtained. Since this relation is so complicated, this problem is solved only numerically [22]. The aim of the present paper is to investigate the growth rate of the KH instability.…”