Does spiral galaxy IC 342 exhibit shear induced wave transformations!?

In this paper we argue that the peculiar magnetic spiral structure of the giant, face-on spiral galaxy IC 342 may be evidence for velocity shear induced magnetohydrodynamic (MHD) density wave transformations.status: publishe

Nonmodal phenomena in differentially rotating dusty plasmas

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Shear-driven wave oscillations in astrophysical flux tubes

In plane-parallel flows velocity shear couples magnetohydrodynamic (MHD) wave modes and induces their mutual transformations. Since the majority of astrophysical flows are not plane-parallel it is important to clarify whether this non-modal phenomenon also takes place in flows with a more complicated spatial geometry and kinematics. The recently devised local method for studying linear perturbation dynamics in flows with arbitrary kinematic complexity is tailor-made for this actual problem. In this paper we apply this new method to the study of velocity shear induced wave transformations in a cylindrical flux tube. We found that the MHD modes sustained by the flux tube flow-the Alfven (AW), the slow magnetosonic (SMW), and the fast magnetosonic (FMW) waves - are efficiently coupled through the agency of the velocity shear. Based on this issue we argue that the individual wave transformation events, happenning perpetually and irregularly in the whole space occupied by the flux tube flow, establish the regime of shear induced wave oscillations throughout the flow. We claim that this previously overlooked linear phenomenon may be important for the generation of solar hydromagnetic waves, for the transmission of the waves through the transition region, for coronal heating and for the acceleration of the solar wind.status: publishe

Shear induced phenomena in dusty plasma flows

It is found that velocity shear enables the extraction of kinetic energy from the background flow by Dust-Acoustic waves. It is also shown that the velocity shear leads to the appearance of a new mode of the dust particles collective behaviour, called shear dust vortices.status: publishe

Are galactic magnetohydrodynamic waves coupled?

Recently, Fan & Lou considered the excitation and time evolution of hydromagnetic density waves in a differentially rotating thin gaseous disc embedded in an azimuthal magnetic field. The authors found that both fast and slow hydromagnetic density waves are amplified while they 'swing' from leading to trailing configurations, and gave a detailed description of the phenomenon. Fan & Lou noticed that the results of their numerical study indicate the existence of a 'coupling' between slow and fast waves.status: publishe

Shear-flow-induced wave couplings in the solar wind

A sheared background flow in a plasma induces coupling between different MHD wave modes, which results in their mutual transformation with corresponding energy redistribution between the modes. In this way, the energy can be transferred from one wave mode to the other, but energy can also be added to or extracted from the background flow. In the present paper we investigate whether the wave coupling and energy transfer mechanisms can operate under solar wind conditions. It is shown that this is indeed the case. Hence, the long-period waves observed in the solar wind at r > 0.3 AU might be generated by much faster periodic oscillations in the photosphere of the Sun. Other possible consequences for the observable peculiar beat phenomena in the wind and acceleration of the wind particles are also discussed.status: publishe

Is the solar corona non-modally self-heated?

Recently it was pointed out that nonmodally (transiently and/or adiabatically) pre-amplified waves in shear flows, undergoing subsequent viscous damping, can ultimately heat the ambient flow. The key ingredient of this process is the ability of waves to grow, by extracting energy from the spatially inhomogeneous mean flow. In this paper we examine this mechanism in the context of the solar coronal plasma flows. "Self-heating" (SH) processes are examined when both viscous damping and magnetic resistivity are at work. We show that if the plasma viscosity is in the favorable range of values the asymptotic SH rate in these flows can be quite substantial.status: publishe

Shear induced phenomena in dusty plasma flows

It is found that velocity shear enables the extraction of kinetic energy from the background flow by Dust-Acoustic waves. It is also shown that the velocity shear leads to the appearance of a new mode of the dust particles collective behaviour, called shear dust vortices.status: publishe

Transient shear instability of differentially rotating and self-gravitating dusty plasma

Recently it was found [Poedts et al., Phys. Plasmas 7, 3204 (2000)] that dusty plasma flows host nonperiodic modes-shear-dust-acoustic (SDA) vortices. These modes, interlaced with dust-acoustic (DA) waves, are able to exchange energy with the ambient flow. In this paper it is studied how these processes evolve in differentially rotating and self-gravitating flows of dusty plasmas. It is found that the presence of the self-gravity and of Coriolis forces makes both SDA vortices and DA waves transiently unstable. It is argued that the transient shear instability could be important for the formation of the fine structure of planetary rings, for the dynamics of charged dust masses and transition to dust-acoustic turbulence in galactic gaseous disks. (C) 2004 American Institute of Physics.status: publishe