Spectral analysis of long wavelength periodic waves and applications.

1997 ◽  
Vol 1997 (491) ◽  
pp. 149-182 ◽  
Author(s):  
Robert A. Gardner
Keyword(s):  
Spectral Analysis ◽  
Periodic Waves ◽  
Long Wavelength

scholarly journals ROLL-WAVES IN BI-LAYER FLOWS

2012 ◽  
Vol 22 (06) ◽  
pp. 1250006 ◽  
Author(s):  
MARC BOUTOUNET ◽  
PASCAL NOBLE ◽  
JEAN-PAUL VILA
Keyword(s):  
Spectral Analysis ◽  
Shallow Water ◽  
Shallow Water Equations ◽  
Low Frequency ◽  
Newtonian Fluids ◽  
Hydrodynamic Instabilities ◽  
Steady Flows ◽  
Long Wavelength ◽  
Roll Waves ◽  
Saint Venant Equations

We derive consistent shallow water equations (so-called Saint Venant equations) for the superposition of two Newtonian fluids flowing down a ramp. We carry out a complete spectral analysis of steady flows in the low frequency/long wavelength regime and show the occurrence of hydrodynamic instabilities, so-called roll-waves, when steady flows are unstable.

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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