Stability of the magnetopause

Kalra, G. L.; Tandon, J. N.; Rajaram, R. Κ.

doi:10.1007/bf00640020

Cited by 6 publications

(6 citation statements)

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“…Pu and Kivelson [1983a,b] examined the detailed mode structure and the possibility of extracting energy from the shear flow in such a system. Rajaram et al [1973] and Kalra et al [1976] studied the effects of pressure anisotropies on the Kelvin-Helmholtz instability. They used the collisionless double adiabatic fluid equations [Chew et al, 1956] and a sharp velocity discontinuity but placed no restriction on the propagation direction, density jump, or rotation of the magnetic field across the tangential boundary.…”

Section: Introductionmentioning

confidence: 99%

Linear theory of the Kelvin‐Helmholtz instability in the low‐latitude boundary layer

Rajaram¹,

Sibeck²,

McEntire³

1991

J. Geophys. Res.

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We examine the stability of the magnetospheric low‐latitude boundary layer to the Kelvin‐Helmholtz instability taking into account the finite thickness of the velocity shear layer, the relative thickness and position of the “current” layer in which the magnetic field rotates from magnetosheath to magnetospheric configurations, and the collisionless and anisotropic nature of the plasmas therein. We show that three factors enhance the instability: (1) a decrease in the thickness of the shear layer, (2) a decrease in the thickness of the current layer (relative to the shear layer), and (3) the proximity of the “current layer” to the outer edge of the shear layer. Although the maximum growth rate occurs for wave numbers roughly equal to the inverse of the semithickness of the shear layer, the velocity threshold for the onset of the instability is insensitive to the thickness. However, when the current layer is displaced from the center toward the outer edge of the shear layer, the threshold is dramatically reduced and the boundary layer can be rendered unstable by relatively small shear flows, suggesting that even the region close to the subsolar point could become unstable when the sheath flow is perpendicular to the magnetospheric magnetic field. This mode can be identified by characteristic profiles across the boundary layer: the plasma density, pressure, and magnetic field strength perturbations all peak near the center of the boundary layer. The transverse magnetic field fluctuations are largest around the current layer, while the radial motions dominate near the inner edge of the boundary layer.

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Section: Introductionmentioning

confidence: 99%

Linear theory of the Kelvin‐Helmholtz instability in the low‐latitude boundary layer

Rajaram¹,

Sibeck²,

McEntire³

1991

J. Geophys. Res.

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“…In this paper, we incorporate these features by using the collisionless, double adiabatic fluid equations (cf. KALRA et al, 1976) to describe the solar wind and magnetospheric plasma.Perturbations of the form exp i(wt+k. r) (where w is the frequency and k is the wave vector) are introduced in the system and the dispersion relation connecting the frequency with kt, the component of the wave vector along the interface, is obtained (cf.…”

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confidence: 99%

“…r) (where w is the frequency and k is the wave vector) are introduced in the system and the dispersion relation connecting the frequency with kt, the component of the wave vector along the interface, is obtained (cf. KALRA et al, 1976).The dispersion relation is solved numerically using relevant solar wind parameters (DOBROWOLNY and MORENA 1975, GOSLING et al, 1976), to determine the stability (growth rate r(=lm(w))<0 corresponds to an instability). The magnetic field and solar wind flow are assumed to be directed radially and the post shock values are obtained from the curves of SPREITER and ALKSNE (1969).…”

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confidence: 99%

“…In this paper, we incorporate these features by using the collisionless, double adiabatic fluid equations (cf. KALRA et al, 1976) to describe the solar wind and magnetospheric plasma.…”

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confidence: 99%

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confidence: 99%

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On the theory of the polarity-independent component of the semiannual variation.

Rajaram¹

1978

J. geomagn. geoelec

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The polarity-independent component of the semiannual variation has been ascribed to the seasonal variation of the threshold of the Kelvin-Helmholtz instability (ROLLER and STOLOV, 1970) in the dawn-dusk sector of the magnetosphere-solar wind boundary which is regarded as a tangential discontinuity separating incompressable magnetized fluids. In this paper, we incorporate these features by using the collisionless, double adiabatic fluid equations (cf. KALRA et al., 1976) to describe the solar wind and magnetospheric plasma.Perturbations of the form exp i(wt+k. r) (where w is the frequency and k is the wave vector) are introduced in the system and the dispersion relation connecting the frequency with kt, the component of the wave vector along the interface, is obtained (cf. KALRA et al., 1976).The dispersion relation is solved numerically using relevant solar wind parameters (DOBROWOLNY and MORENA 1975, GOSLING et al., 1976), to determine the stability (growth rate r(=lm(w))<0 corresponds to an instability). The magnetic field and solar wind flow are assumed to be directed radially and the post shock values are obtained from the curves of SPREITER and ALKSNE (1969). We find that the dawn and dusk region of the magnetopause is unstable irrespective of the season, showing that the variation in the threshold may not be an appropriate source of the magnetic activity. In Fig. 1, the growth rate, chosen as a measure of induced activity, is depicted for three sample solar wind speeds. The amplitude of the semiannual oscillation decreases with the increase in the solar wind velocity. Hence, from GOSLING et al. (1976), the amplitude of the semiannual variation is expected to increase with increase in solar activity provided the density does not also increase from low to high solar activity.

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