摘要:

This paper deals with mode in nonrotating horizontally stratified dusty atmosphere. We have studied dust gravity and acoustic modes in presence of a barometric equilibrium in an unmagnetized dusty plasma. All the dust grains are considered to have same and fixed negative (positive) charge on them. The electron and ions are considered to obey isothermal equations of state while the dust grain are following an adiabatic equation of state. This work can be considered as a generalization of single fluid treatment of gravity-acoustic modes. The analysis of dispersion relation suggests that the dust grains can introduce a new decay length of the perturbation. Therefore we find that the dispersion characteristics of single fluid treatment is strongly modified in the presence of charged dust grain. Finally we discussed importance of our results in the context of planetary and stellar environments. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324927

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Self-gravitating clouds have been shown by Jeans to be unstable to harmonic perturbations whose wavelength exceeds some critical value involving the mass density and some thermal velocity or equivalent information. Based upon the assumption that the unperturbed cloud is initially uniform, the Jeans instability is non-oscillatory and purely growing. However, Newtonian gravitation precludes strictly homogeneous equilibria, but a way out is offered, in theory, by considering local perturbations, small compared to the inhomogeneity scale lengths. While in itself plausible, this procedure can in most cases not be tested for internal consistency, because real knowledge about the equilibrium is lacking, and is therefore called the Jeans swindle. The severe limitations of such an approach lead to an unavoidable dichotomy, and an example of a plasma will be discussed where the computations can be done explicitly, both for the stationary as well as for the perturbed state, showing that the system is stable at all wavelengths compatible with the equilibrium inhomogeneity. Nevertheless, the present state of affairs does not allow self-consistent equilibria to be worked out in more complicated configurations, like in dusty plasmas with external magnetic fields. This typically leads to the Jeans swindle being used a little longer than desirable. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324928

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

In view of various occurrences in space of bounded dusty plasmas, we consider the wave processes in an individual cylindrical dusty self-gravitational flow and in the system of dusty self-gravitating plasma streams interacting through both electric and gravitational forces. Furthermore, we include the effect of an ambient electron-ion plasma, which can play a decisive role in the interaction between dusty flows. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324929

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The study of magnetohydrodynamic waves and instabilities of both laboratory and astrophysical plasmas has been conducted for many years starting from the assumption of static equilibrium. Recently, there is an outburst of interest for plasma states where this assumption is violated. In fusion research, this interest is due to the importance of neutral beam heating and pumped divertor action for the extraction of heat and exhaust needed in future tokamak reactors. Both result in rotation of the plasma with speeds that do not permit the assumption of static equilibrium anymore. In astrophysics, observations in the full range of electromagnetic radiation has revealed the primary importance of plasma flows in such diverse situations as coronal flux tubes, stellar winds, rotating accretion disks, and jets emitted from radio galaxies. These flows have speeds which substantially influence the background stationary equilibrium state, if such a state exists at all. Consequently, it is important to study both the stationary states of magnetized plasmas with flow and the waves and instabilities they exhibit. We will present new results along these lines, extending from the discovery of gaps in the continuous spectrum and low-frequency Alfve´n waves driven by rotation to the nonlinear flow patterns that occur when the background speed traverses the full range from sub-slow to super-fast. The solutions obtained may bridge the gap between insights from linear and nonlinear analyses. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324930

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The physical properties of the minor ions in the corona provide clues on the coronal heating and solar wind acceleration mechanism. Recent observations show that protons and minor ions are hot(Tp>106&hthinsp;K, Ti>108&hthinsp;K)and anisotropic in coronal holes. A possible cause of the large perpendicular motions is unresolved Alfve´nic fluctuations in the solar wind. Using the three-fluid 2.5D MHD model I have shown that the unresolved Alfve´nic fluctuations lead to apparent proton temperature and anisotropy consistent with UVCS observations. I show the calculated dependence of the apparent kinetic temperatures of protons andO5+ions with heliocentric distance and compare the results to the UVCS observations. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324931

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Despite of the large number of models and mechanisms proposed in the literature, the problem of the heating of the solar corona is still unsolved and represents one of the challenge of solar physics. In this context, a basic question to be addressed by any viable theoretical model concerns understanding the mechanism capable of transferring “efficiently” the energy from the large injection scales to the much smaller dissipative scales in an almost ideal plasma where these scales differ by many order of magnitude. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324932

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

In a previous paper we have illustrated the concept of resonant flow instability of the trapped modes both in a 1-D slab model and a 1-D cylindrical model for a coronal plume in a cold plasma. We found that much larger values of the velocity shear are needed for Kelvin-Helmholtz than for resonant instability to occur. The aim of this paper is to study the effect of a non-zero plasma pressure on the eigenmodes of the plume structure. We show that the instability most probably to occur in coronal plumes is due to the resonant coupling of slow body modes to local resonant Alfve´n waves. These instabilities could lead to disruption of the coronal plumes and to the mixing with interplume plasma. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324933

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We study the resonant absorption of fast magnetoacoustic (FMA) waves in inhomogeneous weakly dissipative, isotropic and anisotropic plasmas. The equilibrium states on which the waves are superimposed is static or stationary and are assumed to be in a 1-D planar geometry. The equilibrium model consists of three layers with an inhomogeneous magnetized plasma surrounded by two homogeneous magnetized semi-infinite plasmas. The propagating FMA waves are partly absorbed and partly reflected by coupling to local nonlinear slow magnetohydrodynamic (MHD) waves in the inhomogeneous layer. The dissipation acts only in a narrow layer called thedissipative layerwhich embraces the resonant magnetic surface. In linear theory it has been shown that in the vicinity of the resonant surface the energy density, the amplitudes of waves and the spatial gradients become large, suggesting that in this region nonlinearity might be important. The wave motions far from the dissipative layer are described by the linear, ideal MHD equations, while inside this layer the wave motions are governed by the full system of the dissipative, nonlinear MHD equations. The coefficient of wave energy resonant absorption is derived assuming weak nonlinearity and long-wavelength approximation. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324934

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Small-amplitude magnetohydrodynamic (MHD) waves are studied in a dilute collisionless plasma with an anisotropic pressure distribution. The parallel and perpendicular pressure are defined with the aid of two polytropic pressure laws. For specific values of the polytropic indices, previous results obtained with the usual Chew-Goldberger-Low (CGL) double-adiabatic (i) and double-isothermal (ii) models are recovered. The double-polytropic model can be considered as the counterpart of the single-polytropic model. Dispersion relations for the linear waves are derived and analyzed in the presence of pressure anisotropy. The weakly nonlinear dynamics is shown to be governed by the Benjamin-Ono equation. The results are discussed in the CGL and double-isothermal limits. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324935

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We examine spectral time series of the transition region line O v 629 Å, observed with the Coronal Diagnostic Spectrometer (CDS) on the SoHO spacecraft. Both Fourier and wavelet transforms have been applied independently to the analysis of plume oscillations in order to find the most reliable periods. The wavelet analysis enables us to derive the duration as well as the periods of the oscillations. Our observations indicate the presence of compressional waves with periods of 10–20 minutes. We have also detected a10±2minute periodicity in the network regions of the north polar coronal hole. The waves are produced in short bursts with coherence times of about 20–30 minutes. We interpret these oscillations as outward propagating slow magneto-acoustic waves, which may contribute significantly to the heating of the lower corona by compressive dissipation and which may also provide enough energy flux for the acceleration of the fast solar wind. The data support the idea that the same driver is responsible for the network and plume oscillations with the network providing the magnetic channel through which the waves propagate upwards from the lower atmosphere to the plumes. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324936

出版商:AIP    

年代:1900

数据来源: AIP