共查询到20条相似文献,搜索用时 15 毫秒
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Mohammad Javad Kalaee Yuto Katoh 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
For a particular angle of incidence wave, it is possible for a slow Z-mode wave incident on an inhomogeneous plasma slab to be converted into an LO mode wave. But for another wave normal angle of the incident wave, it has been considered impossible, since an evanescence region exists between two mode branches. In this case we expect that the mode conversion takes place through the tunneling effect. We investigate the effect of the spatial scale of the density gradient on the mode conversion efficiency in an inhomogeneous plasma where the mode conversion can occur only by the tunneling effect. We use the computer simulation solving Maxwell’s equations and the motion of a cold electron fluid. By considering the steepness of the density gradient, the simulation results show the efficient mode conversion could be expected even in the case that the mismatch of the refractive indexes prevents the close coupling of plasma waves. Also, we show for these cases the beaming angle does not correspond to Jones’ formula. This effect leads to the angles larger and smaller than the angle estimated by the formula. This type of mode conversion process becomes important in a case where the different plasmas form a discontinuity at their contact boundary. 相似文献
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与垂直加热相比,斜向加热电离层具有灵活性高、影响范围广和便于实际操作等优势.在非偏区考虑欧姆吸收,基于电子能量方程和连续性方程构建电波斜向加热低电离层的物理模型,并利用IRI-2007和NRLMSISE-00经验模型提供的背景参数对南京地区斜向加热低电离层进行数值模拟,对比不同加热条件下电子温度和电子密度的扰动情况.研究结果表明:电波加热效果随入射仰角和有效辐射功率的增大而增大;电子温度和电子密度增幅随电波频率增大而减小;X波模比O波模造成的电子温度扰动幅度和电子密度扰动幅度更大,同时X波模比O波模能更快地使电子温度和电子密度达到稳定状态;一定范围内较小仰角、较低频率、较大有效辐射功率的电波能使电子密度更快达到稳定,后两者还能加快电子温度达到稳定的过程;电子温度达到稳定所需时间随入射电波仰角呈单峰变化,仰角为62°时达到最大. 相似文献
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U. Mukherjee B. Paul 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2774-2776
High Mass X-ray Binary Pulsars (HMXBP), in which the companion star is a source of supersonic stellar wind, provide a laboratory to probe the velocity and density profile of such winds. Here, we have measured the variation of the absorption column density along with other spectral parameters over the binary orbit for two HMXBP in elliptical orbits, as observed with the Rossi X-ray Timing Explorer (RXTE) and the BeppoSAX satellites. A spherically symmetric wind profile was used as a model to compare the observed column density variations. In 4U 1538-52, we find the model corroborating the observations; whereas in GX 301-2, the stellar wind appears to be very clumpy and a smooth symmetric wind model seems to be inadequate in explaining the variation in column density. 相似文献
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电子在磁场中运动,对频率ωi的外来电磁波的散射,除频率仍为ωi的部分以外,还发出与回旋辐射相同频率的散射波,这可以称作是自激效应.除了高频极限,该效应对散射截面有相当大的影响.本文对单个电子及冷等离子体情形,给出了强磁场中非相对论性经典电子散射截面的修正计算.讨论了电子散射的谱分布,给出某些典型情形中平衡状态下磁等离子体的Thomsom吸收系数.本文结果可应用于X射线脉冲星谱线形成等问题. 相似文献
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A.Y. Wong J. Santoru J.G. Roederer G. Sivjee 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(2):225-228
Laboratory experiments in which high power, pulsed electromagnetic waves interact with an inhomogeneous plasma indicate that the generated nonlinear plasma phenomena depend on peak incident power and not on pulse length. The electromagnetic waves can penetrate beyond the cutoff and produce large, enhanced electrostatic fields at the critical layer within 100 electron plasma periods. The enhanced electric field pressure can be comparable to the thermal pressure and can accelerate ions and electrons to velocities much greater than their thermal speed. Large density cavities (with δn/n ? 10%) can be created in a time shorter than the usual ion response time because of the accelerated ion dynamics. These laboratory results have been extended to create a new and generalized concept to actively stimulate space plasmas with high power pulses of short duration. A field experiment will be used for the stimulation of auroral ionospheric plasma. The ground-based system is modular, each module consisting of a 2 MW pulsed HF transmitter designed at UCLA and a crossed-dipole antenna element. Incoherent scatter radar and optical diagnostic methods are discussed. 相似文献
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Igor Kulikov Anthony J. Mannucci Xiaoqing Pi Carol Raymond George A. Hajj 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
In the coming years, opportunities for remote sensing of electron density in the Earth’s ionosphere will expand with the advent of Galileo, which will become part of the global navigation satellite system (GNSS). Methods for accurate electron density retrieval from radio occultation data continue to improve. We describe a new method of electron density retrieval using total electron content measurements obtained in low Earth orbit. This method can be applied to data from dual-frequency receivers tracking the GPS or Galileo transmitters. This simulation study demonstrates that the method significantly improves retrieval accuracy compared to the standard Abel inversion approach that assumes a spherically symmetric ionosphere. Our method incorporates horizontal gradient information available from global maps of Total Electron Content (TEC), which are available from the International GNSS Service (IGS) on a routine basis. The combination of ground and space measurements allows us to improve the accuracy of electron density profiles near the occultation tangent point in the E and F regions of the ionosphere. 相似文献
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针对多层电离层,采用反抛物层作为连接层来描述电离层之间区域的电子密度分布.以电子密度和其相对于高度的一阶偏导数连续为依据,拟合出连接层的临界频率、半厚度和底高等电离层参数.将电离层的准抛物模型和连接层的反抛物模型中计算出来的等离子频率代入Appleton-Hartree公式和Snell定理,结合射线的几何结构完成多层电离层中的射线追踪,同时计算群路径、相路径和传输距离这3种重要的路径参数.分析当给定频率时,路径参数与入射角之间的关系,群路径、相路径与传输距离之间的关系,频率对路径参数之间变化关系的影响;同时分析了给定入射角时,路径参数与射线工作频率之间关系和入射角对于路径参数之间变化关系的影响. 相似文献
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Sachindra Naik U. Mukherjee B. Paul C.S. Choi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
Our work focuses on a comprehensive orbital phase-dependent spectroscopy of the four High Mass X-ray Binary Pulsars (HMXBPs) 4U 1538-52, GX 301-2, OAO 1657-415 and Vela X-1. We hereby report the measurements of the variation of the absorption column density and iron-line flux along with other spectral parameters over the binary orbit for the above-mentioned HMXBPs in elliptical orbits, as observed with the Rossi X-ray Timing Explorer (RXTE) and the BeppoSAX satellites. A spherically symmetric wind profile was used as a model to compare the observed column density variations. Out of the four pulsars, only in 4U 1538-52, we find the model having a reasonable corroboration with the observations, whereas in the remaining three the stellar wind seems to be clumpy and a smooth symmetric stellar wind model appears to be quite inadequate in explaining the data. Moreover, in GX 301-2, neither the presence of a disk nor a gas stream from the companion was validated. Furthermore, the spectral results obtained in the case of OAO 1657-415 and Vela X-1 were more or less similar to that of GX 301-2. 相似文献
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基于传播矩阵法计算了均匀半空间电离层的反透射系数, 同时解Booker复系数四次方程得到电离层的复折射指数, 分别研究了电离层反射透射系数及折射指数随VLF频段入射电波频率、入射角和地磁倾角、电离层电子浓度及碰撞频率的变化规律. 计算结果表明, 在VLF频段, 垂直电偶极子辐射的横磁(Traverse Magnetic)波更易透射进入电离层, 而水平电偶极子辐射的横电(Traverse Electric) 波易被限制在地-电离层波导内来回反射. 电离层电子密度较低时 (如夜间), 在高纬度地区, 观测到地震电离层VLF异常的概率更大. 当考虑地磁场 的影响时, 电离层将允许地震辐射的超低频(Ultra Low Frequency ,ULF)/甚低频 (Very Low Frequency, VLF)部分的电磁波透射进入电离层, 这一点已有很多卫星观测事实为证, 但其进一步的物理机制尚需深入研究. 相似文献
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《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2001,27(6-7):1259-1263
The r.m.s. errors in ionospheric parameters studied by the vertical HF-sounding method were determined for a monotonic height distribution of the electron density. Numerical estimates were obtained for errors in real heights, in vertical velocities of plasma motion and in effective electron collision frequencies deduced from experimental measurements of virtual heights, Doppler frequency shift and radio wave absorption respectively. Their dependencies on signal polarisation, working frequency range and geo-magnetic latitude of the observation point were determined. 相似文献
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《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1986,6(3):157-175
The plasmasphere is filled with very low energy plasma upwelling from the topside ionosphere. The field-aligned distribution of this thermal ionospheric plasma is controlled by the gravitational and centrifugal potential distribution. There are two extreme types of hydrostatic plasma distribution in this field-aligned potential : the Diffusive Equilibrium distribution and the Exospheric Equilibrium distribution corresponding respectively to a saturated and to an almost empty magnetic flux tube. As a result of pitch angle scattering by Coulomb collisions an increasing number of ions escaping from the ionosphere are stored on trapped orbits with mirror points at high altitudes in the low density region. As a result of collisions the field-aligned density distribution gradually changes from exospheric equilibrium with a highly anisotropic pitch angle (cigar like) distribution to a diffusive equilibrium with a nearly isotropic pitch angle distribution. It is shown that the suprathermal ions become anisotropic much more slowly than ions of energies smaller than 1 eV. The Coulomb collision times have been estimated for flux tubes at different L values. A numerical simulation of the flux tube refilling process has been presented. The diurnal variation of the equatorial plasma density has been illustrated for plasma elements convected along drift paths which have a large dawn- dusk asymetry. The formation of a Light Ion Trough is discussed. Finally, evidence has also been given for the existence of a ‘plasmaspheric wind’ corresponding to a slow subsonic and continuous radial expansion of the plasma stored in the plasmasphere. 相似文献
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S.A. Elwakil M.A. Zahran E.K. El-Shewy A.E. Mowafy 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
A theoretical investigation has been made for adiabatic positive and negative dust charge fluctuations on the propagation of dust-ion acoustic waves (DIAWs) in a weakly inhomogeneous, collisionless, unmagnetized dusty plasmas consisting of cold positive ions, stationary positively and negatively charged dust particles and isothermal electrons. The reductive perturbation method is employed to reduce the basic set of fluid equations to the variable coefficients Korteweg–de Vries (KdV) equation. Either compressive or rarefactive solitons are shown to exist depending on the critical value of the ion density, which in turn, depends on the inhomogeneous distribution of the ion. The dissipative effects of non-adiabatic dust charge variation has been studied which cause generation of dust ion acoustic shock waves governed by KdV-Burger (KdVB) equation. The results of the present investigation may be applicable to some dusty plasma environments, such as dusty plasma existing in polar mesosphere region. 相似文献
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位于波多黎各的Arecibo非相干雷达可以获得低电离层电子和离子密度, 利用此非相干雷达数据对中纬度低电离层的运动特征进行研究. 得到了电子密度随时间和高度的变化 情况, 结果显著呈现出周日变化特征, 并分析了电子密度随高度的变化规律. 进一步对数据进行频谱分析, 深入研究低电离层电子密度的周日变化效应. 得到电子密度的高度剖面, 发现从F层底部到E层有明显的等离子体沉降. 低电离层的层结构特征及电子密度变化表明, 在该区域还存在不同程度的等离子体扰动, 由此对低电离层的作用因素 进行分析, 认为大气潮汐或声重波可能对低电离层产生扰动, 即低电离层与大气存在一定程度的耦合作用. 相似文献
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Yen-Hsyang Chu Chin-Lung SuHsiao-Tsung Ko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
With a network of ground-based ionosondes distributed around the world, the ionospheric peak electron density and its height measured by FORMOSAT-3/COSMIC satellites in terms of GPS radio occultation technique are extensively examined in this article. It is found that, in spite of the latitude, the mean values of the peak electron density measured by COSMIC satellites are systematically smaller than those observed by ground-based ionosondes. The discrepancy between them is dependent on the latitude, namely, it is small in low and mid-latitudes and large in high-latitude region. Moreover, statistical analysis shows that the slopes of the regression line that is best fitted to the scatter diagram of occultation-retrieved peak electron density (ordinate axis) versus ionosonde-observed peak density (abscissa axis) are universally less than one. This feature is believed to be the result of path average effect of non-uniform distribution of the electron density along the GSP ray during the occultation. A comparison between COSMIC-measured peak height and ionosonde-derived peak height hmF2 indicates that the former is systematically higher than the latter. The difference in the two can be as large as 20% or more in equatorial and low-latitude regions. This result implies that the peak height hmF2 derived from the virtual height through true height analysis based on Titheridge method seems to underestimate the true peak height. The correlation between COSMIC and ionosonde peak electron densities is analyzed and the result reveals that correlation coefficient seems to be dependent on the fluctuation of the occultation-retrieved electron density profile. The correlation will be higher (lower) for the electron density profiles with smaller (larger) fluctuations. This feature suggests that the inhomogeneous distribution of the electron density along the GPS ray path during the occultation plays an important role affecting the correlation between COSMIC and ionosonde measurements. 相似文献
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应用解析和数值相结合的方法,本文处理了球对称太阳引力场中具有磁场的非粘、可压缩、完全导电等离子体的二维磁流体动力学平衡问题.得到了两种不同的解:(1)一种相应于磁场具有闭合区和开场区的稳定、自洽的等离子体流动,开场区几个太阳半径之外等离子体径向速度达到大值,超过了局地声速和局地Alfén速度;(2)等离子体速度总是小于局地声速和局地Alfvén速度,并当径向距离很大时速度趋于零. 相似文献