Magnetic shear instability for accretion tori of constant specific angular momentum

1998 ◽  
Author(s):  
Leonardo Primavera ◽  
Günther Rüdiger
Keyword(s):  
Angular Momentum ◽  
Shear Instability ◽  
Magnetic Shear

Reduction in transport by the parallel velocity shear instability due to reversed magnetic shear

2001 ◽  
Vol 8 (8) ◽  
pp. 3645-3651 ◽  
Author(s):  
D. R. McCarthy ◽  
E. J. Fuselier ◽  
S. Sen
Keyword(s):  
Velocity Shear ◽  
Shear Instability ◽  
Magnetic Shear

scholarly journals Can Pulsational Instabilities Impact a Massive Star's Rotational Evolution?

2007 ◽  
Vol 3 (S250) ◽  
pp. 161-166 ◽  
Author(s):  
Rich Townsend ◽  
Jim MacDonald
Keyword(s):  
Molecular Weight ◽  
Angular Momentum ◽  
Significant Role ◽  
Massive Stars ◽  
Shear Instability ◽  
Momentum Transport ◽  
Gradient Zone ◽  
Angular Momentum Transport ◽  
Rotational Evolution

AbstractWe investigate whether angular momentum transport due to unstable pulsation modes can play a significant role in the rotational evolution of massive stars. We find that these modes can redistribute appreciable angular momentum, and moreover trigger shear-instability mixing in the molecular weight gradient zone adjacent to stellar cores, with significant evolutionary impact.

scholarly journals Superrotation Maintained by Meridional Circulation and Waves in a Venus-Like AGCM

2006 ◽  
Vol 63 (12) ◽  
pp. 3296-3314 ◽  
Author(s):  
Masaru Yamamoto ◽  
Masaaki Takahashi
Keyword(s):  
Angular Momentum ◽  
General Circulation ◽  
Meridional Circulation ◽  
Circulation Model ◽  
Shear Instability ◽  
Momentum Transport ◽  
Lower Atmosphere ◽  
Cloud Base ◽  
Temperature Structure ◽  
Angular Momentum Transport

Fully developed superrotation—60 times faster than the planetary rotation (243 days)—is simulated using a Venus-like atmospheric general circulation model (AGCM). The angular momentum of the superrotation is pumped up by the meridional circulation with the help of waves, which accelerate the equatorial zonal flow. The waves generated by solar heating and shear instability play a crucial role in the atmospheric dynamics of the Venusian superrotation. Vertical and horizontal momentum transports of thermal tides maintain the equatorial superrotation in the middle atmosphere, while equatorward eddy momentum flux due to shear instability raises the efficiency of upward angular momentum transport by the meridional circulation in the lower atmosphere. In addition to the superrotation, some waves simulated in the cloud layer are consistent with the observations. The planetary-scale Kelvin wave identified as the near-infrared (NIR) oscillation with periods of 5–6 days is generated by the shear instability near the cloud base, and the temperature structure of the diurnal tide is similar to the infrared (IR) observation near the cloud top. Sensitivities to the bottom boundary conditions are also examined in this paper, since the surface physical processes are still unknown. The decrease of the equator–pole temperature difference and the increase of the surface frictional time constant result in the weaknesses of the meridional circulation and superrotation. In the cases of the weak superrotation, the vertical angular momentum transport due to the meridional circulation is inefficient and the equatorward eddy angular momentum transport is absent near 60-km altitude.

scholarly journals Nova Outbursts Due to Accretion from Rotating H-Rich Disks onto White Dwarfs

1979 ◽  
Vol 53 ◽  
pp. 294-296
Author(s):  
Warren M. Sparks ◽  
G. Siegfried Kutter
Keyword(s):  
Angular Momentum ◽  
White Dwarf ◽  
Shear Instability ◽  
Marginal Stability ◽  
Solar Composition ◽  
Third Stage ◽  
Rich Material ◽  
Nova Outbursts ◽  
Work Done ◽  
Nova Outburst

In this paper we discuss the third stage of our research on the nova outburst as described in the preceeding paper (Kutter and Sparks, page 290), i.e. we accrete hydrogen-rich material (normal solar composition) with Keplerian velocity onto a helium white dwarf at a rate of 10-8 M⊙/yr. When material with high angular momentum from a circumstellar disk is accreted onto a white dwarf with negligible angular momentum, a tremendous shear instability is created, and hydrogen-rich material is mixed with helium-rich material of the white dwarf on a scale that is short compared to the accretion time scale. Following Kippenhahn and Thomas (1978), we assume that in the mixing region marginal stability is established. Mathematically this is expressed by setting the Richardson number (the ratio of the work done against buoyancy to the kinetic energy of the turbulence) equal to ¼.

Activated Prominences; Mechanisms for Activation and Eruption

1979 ◽  
Vol 44 ◽  
pp. 307-313
Author(s):  
D.S. Spicer
Keyword(s):  
Pressure Gradient ◽  
Density Gradient ◽  
Current Density ◽  
Convective Instability ◽  
Tearing Mode ◽  
Magnetic Shear ◽  
Long Wavelength ◽  
Ideal Mhd ◽  
Gradient Change ◽  
Accelerated Particles

A possible relationship between the hot prominence transition sheath, increased internal turbulent and/or helical motion prior to prominence eruption and the prominence eruption (“disparition brusque”) is discussed. The associated darkening of the filament or brightening of the prominence is interpreted as a change in the prominence’s internal pressure gradient which, if of the correct sign, can lead to short wavelength turbulent convection within the prominence. Associated with such a pressure gradient change may be the alteration of the current density gradient within the prominence. Such a change in the current density gradient may also be due to the relative motion of the neighbouring plages thereby increasing the magnetic shear within the prominence, i.e., steepening the current density gradient. Depending on the magnitude of the current density gradient, i.e., magnetic shear, disruption of the prominence can occur by either a long wavelength ideal MHD helical (“kink”) convective instability and/or a long wavelength resistive helical (“kink”) convective instability (tearing mode). The long wavelength ideal MHD helical instability will lead to helical rotation and thus unwinding due to diamagnetic effects and plasma ejections due to convection. The long wavelength resistive helical instability will lead to both unwinding and plasma ejections, but also to accelerated plasma flow, long wavelength magnetic field filamentation, accelerated particles and long wavelength heating internal to the prominence.

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