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1.
A non-local theory is developed to study the Rayleigh–Taylor instability in an inhomogeneous dusty plasma in the presence of a uniform magnetic field. Using the fluid equations and the dynamics of charged dust grains, an eigenmode equation is derived to study the stability of the mode. Typical space parameters in the vicinity of Saturn are used to investigate the stability of the mode. The growth rate of the Rayleigh–Taylor is found to be drastically higher in a dusty plasma than in a pure plasma. This might have a wider consequence in explaining the origin of low-frequency modes in various situations in the space atmosphere. The effects of the dust charge, and the dust density on the growth rate of the instability are also studied. 相似文献
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Satellite observations show that the electrostatic instability, which is expected to occur in most cases due to an inhomogeneous energy density caused by a strongly inhomogeneous transverse electric field (shear of plasma convection velocity), occasionally does not develop inside nonlinear plasma structures in the auroral ionosphere, even though the velocity shear is sufficient for its excitation. In this paper, it is shown that the instability damping can be caused by out-of-phase variations of the electric field and field-aligned current acting in these structures. Therefore, the mismatch of sources of free energy required for the wave generation nearly nullifies their common effect. 相似文献
4.
N. I. Izhovkina 《Geomagnetism and Aeronomy》2010,50(6):788-795
Plasma inhomogeneities extending along geomagnetic field lines in the ionosphere and magnetosphere can have a vortex structure.
Electromagnetic waves can propagate in plasma inhomogeneities in the waveguide channel mode. It has been indicated that energy
and particle fluxes related to the development of small-scale electrostatic turbulence in a magnetized plasma with an unstable
electron component promotes an increase in plasma density gradients in the walls of waveguide channels and an enhancement
in plasma vortices. At low L shells in the region of the geomagnetic equator, the development of plasma electrostatic instability and the damping of drifting
plasma vortices in the inhomogeneous geomagnetic field in the topside ionosphere can be the main mechanism by which large-scale
(∼1000 km) regions with a decreased plasma density are formed. 相似文献
5.
Exposed to space plasma and solar radiation, electrostatic potential may build up in the lunar regolith, leading to a wealth of dust phenomena, including levitation, oscillation, and transport over the surface. Based on plasma sheath theory, the global near-surface plasma environment is modeled, and the dynamics of charged dust are investigated. Results show that sub-micron sized dust particles can be levitated by the electric field over the surface, forming a dust belt that changes in position and thickness depending on the solar zenith angle. On the dayside of the Moon, stably levitated particles are about ten times smaller, and collect in a thinner belt closer to the surface than do those on the nightside. Although the size and charge of stably levitated dust particles are dependent on ambient plasma conditions, initial charge and velocity, which are closely related to the dynamics of dust particles including charging, oscillation, and damping, will determine whether, or not, a particle can attain stable levitation. Horizontal electrostatic dust transport near to the terminator region may lead to net deposition of dust from the dark into the sunlit hemisphere. Finally, because of different charging processes that result due to rotation of the Moon, before precipitation, dust particles in the dusk terminator region may be transported much longer distances and oscillate to much higher altitude than these in the dawn terminator. 相似文献
6.
G. D. Aburjania 《Geomagnetism and Aeronomy》2011,51(6):720-729
The microscopic consequences of the presence of nonlinear vortex structures in the near-Earth plasma dispersive medium are
studied in this work. In dispersive media, strongly localized vortex structures contain trapped particles, cause pronounced
density fluctuations, and intensify transfer processes, mixing in a medium; i.e., they can form strong vortex turbulence.
Turbulence is represented as a gas in the ensemble of strongly localized (therefore, weakly interacting) identical vortices
composing the ground state. Vortices with different amplitudes are randomly located in space (since they interact with one
another) and are described statistically. It is assumed that the steady turbulent state is formed through a balance of mutually
competing effects: spontaneous generation of vortices due to nonlinear steepening of the disturbance front, ^noise transfer
to small scales, and collisional or collisionless damping of disturbances in the HF region. Noise scaling in the inertial
interval takes place since structures merge during their collision. A magnetized plasma medium in the magnetosheath is considered.
A new type of turbulent fluctuation spectra with respect to wavenumbers k
−8/3, which is in satisfactory agreement with satellite observations in space plasma, has been determined. The medium particle
diffusion on an ensemble of vortices has also been studied. It has been established that the interaction between structures
themselves and between structures and medium particles causes anomalous diffusion in the medium. The effective diffusion coefficient
square roothly depends on the noise stationary level. 相似文献
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8.
Effects of molecular ions on the Rayleigh–Taylor instability in the night-time equatorial ionosphere
《Journal of Atmospheric and Solar》1999,61(5):399-405
In view of composition measurements in the night-time equatorial ionosphere, the role of molecular ions on the collisional Rayleigh–Taylor instability is examined using a linear perturbation analysis and a growth rate expression in the presence of double-ion species is obtained. The expression reveals that the growth rate depends on the number densities of both the ion species. This is in contrast to a single ionic constituent wherein the growth rate is independent of number density. The numerical calculation under realistic conditions reveals that the growth rate of the instability reduces with the introduction of the second dominant ion species and never exceeds the growth rate corresponding to a single ionic constituent. Further, the growth of the plasma instability is feasible even when the scale length of the second dominant ion is negative. 相似文献
9.
本文从计入离子-中性粒子碰撞频率Vin效应的等离子体二流体方程组出发,导出统一描述ESF小尺度和中小尺度区域现象的二维静电模型.对模型方程进行了详细的线性波理论分析.结果表明,晚间赤道F层可存在正能波和负能波;Vin效应的影响是否重要依赖于波数和离子梯度漂移速度u_d乘积的大小.在小尺度区域,Vin影响较小,本文模型将变成我们已提出的小尺度无碰撞模型;而在中小尺度区域,Vin效应很重要,本文模型将得到著名的Rayleigh-Taylor不稳定性结果,Vin项对波的影响可以是致稳作用也可能是失稳作用,RT不稳定性波模对应于负能波分支. 相似文献
10.
A theory of the generation of plasma density irregularities with virtually no aspect sensitivity, in the lower ionosphere at high latitudes, by electron drifts aligned with the geomagnetic field, is presented. The theory is developed through fluid equations in which the destabilising mechanism involves positive feedback from electron collisional heating. When field aligned electron drift speeds exceed a few km s–1, this effect destabilises waves with wavelengths in excess of a few tens of metres in the lower E-region, where collisional effects are sufficiently large. Furthermore, the threshold conditions are almost independent of the wave propagation direction and the unstable waves propagate at speeds well below the ion acoustic speed. The role that this new instability may play in recent radar backscatter observations of short scale irregularities propagating in directions close to that of the geomagnetic field, in the lower E-region is also considered. 相似文献
11.
Hessdalen lights (HL) are unexplained light balls usually seen in the valley of Hessdalen, Norway. In this work, it is suggested that HL are formed by a cluster of macroscopic Coulomb crystals in a plasma produced by the ionization of air and dust by alpha particles during radon decay in the dusty atmosphere. Several physical properties (oscillation, geometric structure, and light spectrum) observed in HL phenomenon can be explained through the dust plasma model. 相似文献
12.
We have observed a number of strong echoes with the European incoherent-scatter (EISCAT) UHF (930-MHz) radar at angles 83.5° and 78.6° with the geomagnetic field and at about 100-km altitude north in the auroral zone. The echoes are shortlived and occur in single 2- or 10-s data dumps. They are offset by 125–130 kHz with respect to the transmitted frequency. In most cases the offset compares well with the frequency of gyro lines in the incoherent-scatter spectrum, as given by the standard linear dispersion relation. But sometimes the measured offsets deviate significantly from the model calculations, and the interpretation in terms of gyro lines becomes questionable. The discrepancy could possibly be explained by local deviations in the magnetic field from the model (IGRF 1987), which are generated by incoming particle beams. A more serious problem with the gyro-line theory is how the line can be excited at altitudes where the collisional damping is substantial. The high intensity and short lifetime of the signal point to a fast-growing plasma instability as the likely excitation mechanism, if the gyro-line interpretation is correct. The cause of the instability could be the same particle beams as those causing the disturbances in the magnetic field. Alternatively, the observations may be interpreted as meteor head echoes. The large Doppler shifts, the short lifetimes and the altitudes of the signals support this explanation. The main difficulty is that the distribution of measured offsets appears to be different in magnetically active conditions and in less active conditions. Also, the occurrence of echoes does not seem to follow the expected changes in meteor density. More observations in different conditions are needed to decide between the two interpretations. As it is, we are inclined to believe in the meteor head echo theory, the objections to the gyro-line theory being more fundamental. 相似文献
13.
L.J. Srnka 《Physics of the Earth and Planetary Interiors》1977,14(3):321-329
When the relative velocity between magnetized plasma and neutral gas exceeds a critical value, the gas-plasma interaction is dominated by collective phenomena which rapidly excite and ionize the neutrals. The interaction of the solar wind with a large cloud (1024 – 1028 neutrals) vented from the moon should be of this type. Line radiation from such an interaction can yield an apparent lunar surface brightness rivaling reflected sunlight levels over small areas, if the kinetic energy flow density of the gas is sufficiently high. The aberrated solar wind flow past the moon would enhance the visibility of such interactions near the lunar sunrise terminator, supporting the statistical studies which indicate that the “Lunar Transient Phenomena” (anomalous optical phenomena on the moon) are significantly correlated with the position of the terminator on the lunar surface. 相似文献
14.
A spherical plasma inhomogeneity located at mesospheric altitudes in a thundercloud quasi-electrostatic field is considered as a possible cause of sprite formation. A simple semianalytical model of ionization instability in a quasi-electrostatic field, the value of which is larger than the air breakdown value, is developed on the assumption that plasma ball conductivity is controlled by impact ionization and electron attachment to neutrals. After several simplifications, the problem is reduced to a system of ordinary differential equations for the average conductivity and plasma ball radius. The analytical estimates and numerical simulation indicate that the predicted expansion rate and acceleration of the plasma inhomogeneity boundary are close in magnitude to the values observed during high-speed imaging of sprite development. 相似文献
15.
Situations when localized precipitation of energetic (E > 30 keV) protons and electrons, associated with the development of cyclotron instability in the magnetosphere, is recorded during one satellite pass are identified in the data of particle flux observations on the NOAA-12 low-orbiting satellite. Such events were observed only in the evening sector of the magnetosphere. This precipitation is compared with the data on the cold (E < 10 eV) plasma density obtained on the LANL geostationary satellites. The comparison showed that the precipitation of energetic particles is related to the presence of cold plasma with a density of 20–100 cm?3 in geostationary orbit in the evening sector of the magnetosphere. The conclusion has been made that the localized precipitation of energetic particles is generated at the edges of small-scale structures of cold plasma, forming the so-called “plasmaspheric tail,” i.e., the cold plasma region extending from the evening plasmapause toward the Sun. 相似文献
16.
S. I. Musatenko Yu. S. Musatenko E. V. Kurochka A. V. Lastochkin V. Ya. Cholij O. I. Maksimenko A. S. Slipchenko 《Geomagnetism and Aeronomy》2006,46(2):173-182
The emission (or modulation) line, which manifests itself during high-speed (the speed of entry into the atmosphere is about 70 km/s) meteor showers (Perseids, Orionids, Leonids), has been detected in the fluctuation spectra of ionospheric plasma radio noise at λ = 2 m. The line frequency varies from 12 to 60 Hz depending on activity of ionospheric ionization sources and local characteristics of a meteor shower, time of day, etc. The line has a width of 2–3 Hz and can have satellites. The dusty plasma characteristics have been estimated on the assumption that ionospheric noise is modulated or emitted due to dusty plasma oscillations. 相似文献
17.
Yu. V. Kyzyurov 《Annales Geophysicae》2000,18(10):1283-1292
We discuss the creation of mid-latitude sporadic-E plasma irregularities (with length-scales smaller than sporadic layer thickness) by the neutral atmosphere turbulence. Using fluid equations, the relation between plasma density fluctuations and the velocity field of neutrals is derived. After a brief discussion of the relevant neutral turbulence, the analytical expression for the power spectrum of plasma irregularities is obtained. This expression allows a power-law type of experimental irregularity spectra (the spectral index depends on sporadic-E characteristics) and possible departures in detail of the irregularity spectra from the power-law form to be explained. In addition, it allows us to make estimates of length-scales at which such departures must occur. 相似文献
18.
The expression for the increment of instability and decrement of diffusion damping of gradient drift waves for ionospheric
altitudes above the F
2 layer maximum is obtained. The gradient drift instability is used to interpret the observations of spread F in the region of large-scale horizontal irregularities of the electron density. Two types of such irregularities observed
on board the Intercosmos-19 (IC-19) satellite in the region of low latitudes (a peak of the density in the dusk ionosphere
and a trough of the density in the dawn ionosphere) are considered. It is shown that the observed gradients of the density
and electric field values in the dawn and dusk ionospheric sectors are quite sufficient for the instability development criterion
to be satisfied in both considered cases. 相似文献
19.
The structure and dynamics of ion-acoustic waves in an unmagnetized plasma, including the case of weakly relativistic collisional plasma (when it is necessary to take into account the high energy particle flows which are observed in the magnetospheric plasma), are studied analytically and numerically on the basis of a model of the Kadomtsev-Petviashvili (KP) equation. It is shown that, if the velocity of plasma particles approaches the speed of light, the relativistic effects start to strongly influence on the wave characteristics, such as its phase velocity, amplitude, and characteristic wavelength, with the propagation of the twodimensional solitary ion-acoustic wave. The results can be used in the study of nonlinear wave processes in the magnetosphere and in laser and astrophysical plasma. 相似文献
20.
Plasma vortices in the ionosphere and atmosphere 总被引：1，自引：0，他引：1
N. I. Izhovkina 《Geomagnetism and Aeronomy》2014,54(6):802-812
Vortices observed in ionized clouds of thunderstorm fronts have the nature of plasma vortices. In this work, the need to account for the electrostatic instability of plasma in the origination, intensification, and decay of plasma vortices in the atmosphere is shown. Moisture condensation results in mass-energy transfer under the inhomogeneous spatial distribution of aerosols. If a phase volume of natural oscillations is transformed in the frequency-wave vector space in inhomogeneous plasma, the damping of plasma oscillations promotes an increase in the pressure gradients normal to the geomagnetic field. Excitation of the gradient instabilities is probable in atmospheric plasma formations. 相似文献