共查询到20条相似文献，搜索用时 288 毫秒
1.
The nighttime winter anomaly (NWA) effect was observed during solar minimum conditions at the American sector by means of ionospheric electron content and vertical sounding measurements in Havana (Cuba). An effective interhemispheric transport of plasma is suggested to explain enhanced northern nighttime ionization during winter solstice. To elucidate this effect, an adequate physicalnumerical model of the coupled system ionosphere-plasmasphere is presented and applied to a corotating tube of plasma at L=1.5 in the American sector. The NWA can be explained by theoretically derived higher tube content during the December solstice and accordingly by more intense nighttime fluxes from the plasmasphere, compared to the June solstice. 相似文献
2.
N.T. Afanasiev A.N. Afanasiev O.A. Larunin V.P. Markov 《Journal of Atmospheric and Solar》2010,72(7-8):583-587
We examine the problem of small-angle scattering of radio waves experiencing total reflection from a randomly inhomogeneous layer of plasma. We consider the waves to be normally incident on the layer. To take into account the scattering peculiarities in the neighborhood of the reflection point, we introduce an analytical transformation for the eikonal equation solution derived by the perturbation method. This transformation permits calculations of radio-wave phase fluctuations for any monotonous profile of the regular dielectric permittivity of the plasma in the layer. Using this approach, we have derived analytical formulas for the variance and two-dimensional spatial spectrum of phase fluctuations, depending on the three-dimensional power spectrum of plasma fluctuations. We have also estimated a contribution of reflection point fluctuations to the phase fluctuations and determined the limits of applicability of the derived formulas. The presented analytical transformation of the eikonal equation solution can be used to calculate other statistical moments of the radio wave phase in many problems of solar–terrestrial physics where scattering and reflection of radio waves by plasma formations are important. 相似文献
3.
The plasma dispersion function and the reduced velocity distribution function are calculated numerically for any arbitrary velocity distribution function with cylindrical symmetry along the magnetic field. The electron velocity distribution is separated into two distributions representing the distribution of the ambient electrons and the suprathermal electrons. The velocity distribution function of the ambient electrons is modelled by a near-Maxwellian distribution function in presence of a temperature gradient and a potential electric field. The velocity distribution function of the suprathermal electrons is derived from a numerical model of the angular energy flux spectrum obtained by solving the transport equation of electrons. The numerical method used to calculate the plasma dispersion function and the reduced velocity distribution is described. The numerical code is used with simulated data to evaluate the Doppler frequency asymmetry between the up- and downshifted plasma lines of the incoherent-scatter plasma lines at different wave vectors. It is shown that the observed Doppler asymmetry is more dependent on deviation from the Maxwellian through the thermal part for high-frequency radars, while for low-frequency radars the Doppler asymmetry depends more on the presence of a suprathermal population. It is also seen that the full evaluation of the plasma dispersion function gives larger Doppler asymmetry than the heat flow approximation for Langmuir waves with phase velocity about three to six times the mean thermal velocity. For such waves the moment expansion of the dispersion function is not fully valid and the full calculation of the dispersion function is needed. 相似文献
4.
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
5.
本文研究了磁层顶等离子体的一个基本模型,得到了一新的非线性常微分方程组.数值分析表明,在一定的磁Reynolds数范围内,系统呈现混沌行为,相轨道趋向于奇异吸引子. 相似文献
6.
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
7.
The dispersive properties of a magnetized plasma with strong short-scale field-aligned irregularities are investigated, and the dielectric permittivity tensor is derived. The components of this tensor are analyzed, and the limits of applicability of the approach used are discussed. The results obtained will be useful with regard to radio wave propagation and electromagnetic wave generation by superthermal electrons in magnetized plasmas containing such irregularities. 相似文献
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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.
D. W. Idenden R. J. Moffett S. Quegan T. J. Fuller-Rowell 《Annales Geophysicae》1997,14(11):1159-1169
A fully time-dependent ionospheric convection model, in which electric potentials are derived by an analytic solution of Laplaces equation, is described. This model has been developed to replace the empirically derived average convection patterns currently used routinely in the Sheffield/SEL/UCL coupled thermosphere/ionosphere/plasmasphere model (CTIP) for modelling disturbed periods. Illustrative studies of such periods indicate that, for the electric field pulsation periods imposed, long-term averages of parameters such as Joule heating and plasma density have significantly different values in a time-dependent model compared to those derived under the same mean conditions in a steady-state model. These differences are indicative of the highly non-linear nature of the processes involved. 相似文献
11.
A. G. Demekhov A. A. Lyubchich V. Y. Trakhtengerts E. E. Titova J. Manninen T. Turunen 《Annales Geophysicae》1998,16(11):1455-1460
We study a simple self-consistent model of a whistler cyclotron maser derived from the full set of quasi-linear equations. We employ numerical calculations to demonstrate dependencies of pulsation regimes of whistler-mode wave interactions with energetic electrons on plasma parameters. Possible temporal evolution of those regimes in real conditions is discussed; calculations are compared with case-study experimental data on energetic electron precipitation pulsations. A reasonable agreement of the model results and the observations has been found. 相似文献
12.
New results on the information that can be extracted from simulated non-Maxwellian incoherent radar spectra are presented. The cases of a pure ionosphere and of a composite ionosphere typical of a given altitude of the auroral F region are considered. In the case of a pure ionosphere of NO+ or O+ ions it has been shown that the electron temperature and the electron density can be derived from a Maxweilian analysis of radar spectra measured at aspect angles of 0° or 21° respectively; the ion temperature and ion temperature anisotropy can be derived from a non- constraining model such as the ID Raman fitting of a complementary measurement made at an aspect angle larger than 0° for the NO+ ions, or at an aspect angle larger than 21° for the O+ ions. Moreover with such measurements at large aspect angles, the shape of the velocity ion distribution functions can simultaneously be inferred. The case of a composite ionosphere of atomic O+ and molecular NO+ions is a difficult challenge which requires simultaneously a complementary measurement of the electron temperature to provide the ion composition and the electron density from the incoherent radar spectra at a specific aspect angle of 21°; hence, a model dependent routine is necessary to derive the ion temperatures and ion temperature anisotropies. In the case where the electron temperature is not given, a routine which depends on ion distribution models is required first: the better the ion distribution models are, the more accurately derived the plasma parameters will be. In both cases of a composite ionosphere, the 1D Raman fitting can be used to keep a check on the validity of the results provided by the ion distribution model dependent routine. 相似文献
13.
《Journal of Atmospheric and Solar》2000,62(10):851-863
Low-altitude satellites make latitudinal cuts through the entire plasma sheet within a few minutes. We show that by combining several such satellites it is possible to form an image of a large portion of the plasma sheet within a relatively short time. Strictly speaking such a technique images the field-aligned portion of the plasma sheet, however, theoretical work as well as extensive in situ observations have demonstrated that the plasma sheet is highly isotropic. In practice the most significant limitation is that electron acceleration events (including the auroral bulge) require discarding the associated ion data. An instance when five DMSP satellites (F10–F14) went through the southern hemisphere nightside oval within a 19 min period is used to construct the first partial magnetotail image. The possibilities of combining data from other missions to construct more complete composite images is considered. This technique is also highly useful in statistical studies of the plasma sheet. Because a low-altitude spacecraft cuts through the plasma sheet about 25 times as often as a mid-altitude spacecraft, and hundreds of times more often than high-altitude spacecraft, statistically meaningful surveys of the plasma sheet as a whole are hundreds of times easier using a collection of DMSP satellites. We demonstrate herein that the dawn LLBL flank is an apparent source of cold magnetosheath plasma supplied to the central plasma sheet. 相似文献
14.
The formation of a neutral induced weak nonlinear shock structure in a weakly ionised magnetoplasma has been analytically investigated. Using the reductive perturbation method, basic dynamical equations of a three-component (electron, ion and neutral) plasma have been reduced to a well-known Burger equation which can support a weak shock solution. Its stationary and initial value solutions have been derived to describe the characteristics of the weak shock profile. Asymptotic behavior of the Burger solution results in a saw-tooth structure which has a practical implication to predict the nonlinear steepened structure of the nighttime irregularity in the lower portion of the Earth’s ionosphere. Accordingly, it is suggested that the observation of saw-tooth shape of nighttime irregularity at 92 km could be attributed to the nonlinear saturation of the NILF mode instability as proposed by Dwivedi and Das in 1992. However, exact experimental verification of this suggestion requires more data on nighttime irregularity in the mesosphere and lower thermosphere (80-95 km) for a wide range of scale sizes extending up to about 1 km and above. 相似文献
15.
Long series of simultaneous VHF scintillation observations at two stations situated in near magnetic east-west direction in the vicinity of the dip equator in the Indian region have been employed to investigate the night-time ionospheric plasma zonal drifts. The drifts are found to be predominantly easterly. On comparing the magnitudes of the drifts with those results derived earlier by HF fading technique, monitoring signals from two satellites at a station and spaced receiver experiment, their associations with the season and the degree of solar activity are discussed. On a broader scale, the annual mean sunspot number is shown to have a direct control on the derived drift, the positive relationship even on day to day basis with the solar flux is established. However, the relationship, as understood by the slope of the best fit line, in the Indian region (0.27) is found to be weaker when compared with the similar slope (0.45) in the American sector. There appears to be no geomagnetic activity control on the estimated drifts. 相似文献
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本文分析了2001年2月和3月期间Cluster Ⅱ穿越磁层顶前后的观测资料,检测到13个通量传输事件（FTEs）.用多颗卫星磁场测量资料的最小方差分析（MVAB）方法确定FTE的管轴方向（其中6个方向较可靠）.FTE管轴方向的分布和低纬处不同,在磁顶法线坐标系LMN中对M轴有较大偏离,比较靠近L轴.deHoffmann Teller(HT)分析指出,13个FTEs都存在一个很好的HT参考系,表明它们以一个准稳的MHD结构运动.对垂直于管轴方向的运动分析表明FTEs并不一定和背景等离子体一起对流,它们可快于或慢于背景流,但FTEs的运动和背景流基本沿相同方向,其间可有一不大的夹角.在HT坐标系中,10个FTEs的等离子体速度接近零, 其他3个FTEs的等离子体速度约为局地Alfven波速的14%,都不符合Walen关系.其中北半球事件的Walen曲线为正斜率,南半球事件为负斜率,这说明等离子体沿磁力线（北半球顺着磁场,南半球逆着磁场）流向磁层. 相似文献
18.
A. Belehaki E. T. Sarris G. Tsiropoula R. W. McEntire S. Kokubun T. Yamamoto 《Annales Geophysicae》1997,15(12):1515-1531
Geotail energetic particle, magnetic field data and plasma observations (EPIC, MGF and CPI experiments) have been examined for a number of energetic particle bursts in the distant tail (120Re < |XGSM| < 130 Re), associated with moving magnetic field structures, following substorm onsets. The features obtained from this data analysis are consistent with the distant magnetotail dynamics determined first by ISEE3 observations and explained in terms of the neutral line model. At the onset of the bursts, before plasma sheet entrance, energetic electrons appear as a field-aligned beam flowing in the tailward direction, followed by anisotro-pic ions. Within the flux rope region, suprathermal ions exhibit a convective anisotropy, which allows determination of the plasma flow velocity, assuming that the anisotropy arises from the Compton-Getting effect. The velocities thus determined in the plasma sheet are estimated to be 200–650 km/s, and compare favourably with the velocities derived from the CPI electron and proton experiment. The estimated length of magnetic field structures varies between 28 and 56 Re and depends on the strength of the westward electrojet intensification. Finally, the three structures reported here show clear magnetic field signatures of flux rope topology. The existence of a strong magnetic field aligned approximately along the Y-axis and centred on the north-to-south excursion of the field, and the bipolar signature in both By and/or Bz components, is consistent with the existence of closed field lines extending from Earth and wrapping around the core of the flux rope structure. 相似文献
19.
Causes of spatial compositional variations in Mariana arc lavas: Trace element evidence 总被引：3，自引：0，他引：3
New inductively coupled plasma mass spectrometry (ICP-MS) trace element data are presented on a suite of arc lavas from the northern Mariana and southern Bonin island arcs. The samples were dredged from seamounts in the Central Island Province (CIP), the Northern Seamount Province (NSP) and the Volcano Arc (VA), and they range in composition from low-K tholeiites to shoshonites. Previous studies on these samples concluded that the primary compositional control was two-component mixing between a fluid-metasomatized mid-ocean ridge basalt (MORB) source and an enriched, ocean island basalt (OIB)-like, mantle component, with subducted sediment material playing a secondary role. However, the new trace element data suggest that the compositional variations along the Mariana arc can be better explained by the addition of spatially varying subduction components to a spatially varying mantle source. The data suggest that the subduction component in the CIP and VA is dominated by aqueous fluids derived from altered oceanic crust and a pelagic sediment component, while the subduction component in the NSP is dominated by more silicic fluids derived from volcanogenic sediments as well as from pelagic sediment and altered oceanic crust. The mantle wedge in the CIP and VA is depleted relative to a normal mid-ocean ridge basalt source by loss of a small melt fraction, while the mantle wedge in the NSP is enriched either by possible gain of a small melt fraction or addition of a sediment-derived melt. Because the subduction of seamounts controls the arc and back-arc geometries, so the concomitant variation between subducted material and mantle composition may be no coincidence. The high field strength element (HFSE) data indicate a high degree of melting (∼ 25–30%) throughout the arc, ∼ 10% of which may be attributed to decompression and ∼ 20% to fluid addition. 相似文献
20.
《Journal of Atmospheric and Solar》2005,67(14):1315-1320
We discuss the coupled expansion of a plasma cloud and a neutral gas, both originating from a point-like source located in space and submitted to the action of an external flux of ionizing radiation. This problem is relevant to the artificial magnetospheric propulsion scheme for solar system exploration. We establish the relevant space and time scales for particle diffusion and plasma bubble formation. Emphasis is placed on the low ionization and high collisionallity of the plasma near the point source, leading to the existence of a small ionosphere surrounding the source, where (contrary to the more common views of this propulsion scheme) the ions are not magnetized. The possibility of direct plasma creation by an initial purely neutral gas release is also envisaged. 相似文献