大尺度赤道扩展F的数值模拟

利用数值模拟，研究了不同条件下赤道电离层等离子体交换不稳定性的演变和扩展Ｆ不均匀体的形态。使用一维或二维初始密度扰动时，交换不稳定性可以发展成为等离子体泡，但不能产生泡壁上的羽毛状结构．大气重力波触发的交换不稳定性能在更短的时间内增长成为等离子体泡．当使用重力波和一个较小尺度密度扰动作为初始扰动时，重力波确定了赤道扩展Ｆ不均匀体的外尺度，较小尺度密度扰动则增长成为泡壁上的羽毛状结构．数值模拟结果与大量观测现象符合得很好 关键词：     

大气重力波产生中纬电离层不均匀体的理论

研究中纬电高层Ｆ区大尺度不均匀休的基本性质及其与大气重力波的关系。分析了等离子体Ｐｅｒｋｉｎｓ不稳定性的非线性发展，发现这种不稳定性饱和在很小的幅度上。讨论了Ｐｅｒｋｉｎｓ不稳定性与重力波的耦合，表明重力波能触发中纬电离层Ｆ区等离子体不稳定性。由重力波触发的等离子体不稳定性可能演变成大幅度的波形结构，空间和时间调制的不均匀体理论揭示了大尺度中纬电离层不均匀体的产生机制。 关键词：     

热电子等离子体低频不稳定性的非线性理论

本文分析了热电子等离子体中低频漂移不稳定性和交换不稳定性的非线性性质,导出了扰动幅度随时间变化的非线性耦合方程,得到了等离子体密度扰动的饱和幅度,讨论了热电子成分对饱和幅度的影响。漂移波引起的等离子体密度扰动相对幅度约20％,交换模引起的等离子体密度相对扰动幅度约5％。当热电子成分达到线性稳定条件所要求的阈值时,漂移波和交换模的饱和幅度降为零。 关键词：     

等离子体交换不稳定性的模耦合理论

本文研究部分电离等离子体中交换不稳定性的爆炸型模耦合。从磁流体动力学方程出发,导出交换模相干三波相互作用的模耦合方程,分析产生爆炸不稳定的可能的耦合类型,具体讨论产生爆炸不稳定的条件。结果表明,非线性效应能使交换模达到饱和状态表现为小幅度的正弦型扰动,也能通过模耦合而导致大幅度扰动的爆发。本文的分析,适用于磁镜位形的等离子体和电离层等离子体。 关键词：     

相对论效应对大振幅电子等离子体振荡破裂影响的数值模拟

通过数值求解符拉索夫方程和泊松方程，研究了相对论效应和温度效应对等离子体振荡破裂的影响. 不考虑相对论效应情况下，初始扰动幅度较小时，不会发生等离子体振荡破裂，系统具有时间周期性. 此时电子温度的增加，会使得等离子体振荡最大幅度减小. 考虑相对论效应时，即使初始的等离子体电子密度扰动幅度不大，随着时间演化，相对论效应也能导致等离子体振荡破裂，而且初始电子密度扰动越小，产生等离子体振荡破裂所需时间越长. 在初始电子密度扰动较大时，无论考虑和不考虑相对论效应都会出现波破裂，但两者的结果有很大不同. 此外温度效应会降低能发生等离子体波破裂的阈值；等离子体波的相速度越大，能产生的波破裂现象也越明显. 关键词： 等离子体振荡 相对论效应 振荡破裂     

热电子对低频等离子体漂移波的稳定作用

本文用磁流体理论导出了热电子等离子体中,等离子体密度梯度驱动的低频漂移波的色散关系,分析了热电子的稳定作用。热电子成分稳定等离子体低频扰动的物理机制是charge uncovering效应,它只依赖于热电子同等离子体的密度比α,而不依赖于热电子的β值。热电子能降低等离子体交换模和漂移波的增长率,减少漂移波引起的等离子体反常输运损失。稳定等离子体交换模要求α≈2％,稳定等离子体漂移波要求α≈40％。理论上预示了在热电子等离子体中,等离子体漂移波是最重要的低频不稳定性。 关键词：     

斜入射非线性电离层Langmuir扰动的电磁波传播特性

基于广义Zakharov模型,结合斜入射等离子体的时域有限差分(FDTD)方法与双流体力学方程,通过由二维麦克斯韦方程等价转换的一维麦克斯韦方程,与等离子体流体力学方程建立了一个电磁波以不同角度入射电离层传播的数值模型.分析推导出TE_z波在斜入射非线性电离层等离子体的支配方程,然后推导了适用于计算电离层电磁波传播特性的FDTD算法.通过仿真来证明该方法在较小倾角下,电磁波对电离层加热形成Langmuir扰动及其传播特性的准确性和有效性.结果表明,在小角度入射下,大功率高频电磁波在电离层等离子体中的O波反射点附近激发出了Langmuir波,同时波粒相互作用导致O波转换为Z波并向电离层更高区域传播.本文进一步研究了基于电离层等离子体的电磁波传播特性,为全面深入分析电离层Langmuir扰动对电离层电波传播特性影响奠定数值算法的基础.     

简单磁镜中热电子等离子体的基本特性

本文叙述了简单磁镜中,热电子等离子体的实验结果。微波在基频共振层击穿气体产生等离子体,二次偕振加热产生热电子环。等离子体激发了低频交换模和漂移波,热电子环对等离子体的扰动有稳定作用。     

化学复合率对激发赤道等离子体泡影响的数值模拟

本文模拟研究了背景电离层在一维和二维扰动下产生等离子体泡的过程,在模拟过程中引入行进式电离层扰动(traveling ionosphere disturbances,TIDs)模型激发生成电子密度的二维扰动,同时通过改变化学复合率来研究不同复合率对等离子体泡结构形态的影响.模拟结果表明,复合率对等离子体泡的生成速度有较大影响,复合率越大,激发等离子体泡所需时间越长.另外,在二维扰动情况下电离层生成等离子体泡的速度要比一维扰动情况下的速度慢.在一维扰动情况下,不同复合率对等离子体泡结构形态影响不大,而在TIDs激发的等离子体泡中,不同复合率对等离子体泡的结构形态有较大影响.在较小复合率的情况下,TIDs激发的等离子体泡可以产生分叉结构,并伴有大量小尺度的等离子体泡结构,同时模拟结果存在等离子体泡底部收缩现象.模拟结果还表明,当存在大量小尺度等离子体泡时,单个等离子体泡周围的极化电场方向在非线性的演化过程中可能会发生变化,因此并不是所有底部等离子体泡都能够抬升到电离层顶部,只有其周围极化电场方向一直是东向的等离子体泡,才能够进一步抬升到电离层顶部.     

基于化学物质释放的电离层闪烁抑制方法研究

中低纬地区经常发生的电离层闪烁,严重影响卫星链路的无线电信号传播过程,导致卫星通信导航信号质量下降,甚至中断.在电离层闪烁发生前的酝酿生成期,通过向电离层闪烁"种子因素"的等离子体泡内释放电子密度增强类化学物质,填充等离子体泡,改变等离子体环境特性,调控电离层动力学过程,能够降低电离层等离子体不稳定性增长率,进而抑制闪烁的发生.本文开展了基于化学物质释放的电离层闪烁抑制理论及方法研究,根据化学物质释放对电离层等离子体环境的影响,定量计算控制因素改变对不稳定性增长率的贡献,建立了基于电子密度增强类化学物质释放的电离层闪烁抑制物理模型,仿真了等离子体泡的填充过程及等离子体不稳定性增长率的演化过程.仿真结果表明该方法具有较好的闪烁抑制效果,为我国中低纬地区卫星信号电离层闪烁抑制研究奠定了理论基础.     

切变基本纬向流中β效应的赤道Rossby孤立波包

从描写赤道Rossby 波的正压大气位涡方程出发,采用多重尺度摄动方法推导出在切变基本纬向流中具有β效应的非线性赤道Rossby波包演变满足非线性Schrdinger方程,并得到单个包络孤立子波解,分析了基本切变流,β效应对非线性赤道Rossby波的影响. 关键词： 赤道Rossby波 β效应 非线性Schrö dinger方程 包络孤立子     

Application of higher-order KdV——mKdV model with higher-degree nonlinear terms to gravity waves in atmosphere

Higher-order Korteweg-de Vries (KdV)-modified KdV (mKdV) equations with a higher-degree of nonlinear terms are derived from a simple incompressible non-hydrostatic Boussinesq equation set in atmosphere and are used to investigate gravity waves in atmosphere. By taking advantage of the auxiliary nonlinear ordinary differential equation, periodic wave and solitary wave solutions of the fifth-order KdV--mKdV models with higher-degree nonlinear terms are obtained under some constraint conditions. The analysis shows that the propagation and the periodic structures of gravity waves depend on the properties of the slope of line of constant phase and atmospheric stability. The Jacobi elliptic function wave and solitary wave solutions with slowly varying amplitude are transformed into triangular waves with the abruptly varying amplitude and breaking gravity waves under the effect of atmospheric instability.     

MHD Wave Interaction within a Plasma Perturbed by Alfvén Waves

The interaction between fast magnetoacoustic waves within a plasma with periodical nonhomogeneities, perturbed by Alfvén waves has been studied. It has been ascertained the appearance of phenomena of a decay instability and an instability involving an increase of the amplitude oscillations. A study of the influence of perturbed plasma parameters on these instability phenomena has been made. It has been found that the optimal perturbing frequency for giving rise to the instability phenomenon is twice the frequency of fast magnetoacoustic waves.     

Dissipation of Nonlinear Wave in Inhomogeneous Dust Plasma Crystal

A Korteweg-de Vires-type (KdV-type) equation and a modifiedNonlinear Schrödinger equation (NLSE) for the dust lattice wave(DLW) are derived in a weakly inhomogeneous dust plasma crystal. Itseems that the amplitude and the velocity of the dust lattice solitary waves decay exponentially with increasing time in a dust lattice. The modulational instability of this dust lattice envelope waves is investigated as well. It is found that the waves are modulational stable under certain conditions. On the other hand, the waves are modulational unstable if the conditions are not satisfied.     

Equatorial Rossby Solitary Wave Under the External Forcing

A simple shallow-water model with influence of external forcing on a β-plane is applied to investigate the nonlinear equatorial Rossby waves in a shear flow. By the perturbation method, the extended variable-coefficient KdV equation under an external forcing is derived for large amplitude equatorial Rossby wave in a shear flow. And then various periodic-like structures for these equatorial Rossby waves are obtained with the help of Jacobi elliptic functions. It is shown that the external forcing plays an important role in various periodic-like structures.     

On stochastic stabilization of the Kelvin-Helmholtz instability by three-wave resonant interaction

An analytical investigation of the effect of three-wave resonant interactions with the linearly unstable wave is proposed. We consider the waves in the Kelvin-Helmholtz model, consisting of two fluid layers with different densities and velocities. We suppose that the velocity shear is weakly supercritical, the instability is of the algebraic type, i.e., the amplitude of the unstable wave grows linearly, and the instability occurs within the framework of a single mode. The amplitudes of two other waves taking part in the nonlinear interaction are assumed to be stable. The initial amplitudes of these waves are supposed to be small in comparison with the initial amplitude of the unstable wave. We present an analysis of the system of amplitude equations derived for this case using JWKB-method. As a result, we obtain equations that couple solutions pre- and post-passing the singular point, i.e., the point where the amplitude of the unstable wave has a local minimum. These equations give us the transformation rule of a parameter that characterizes the phase shift between fast and slow waves and defines the behavior of the system. This parameter is constant between two singular points and varies by chance at a singular point. As long as it stays positive, the amplitude of the wave remains limited and performs stochastic oscillations. If this parameter passes over zero, then we leave the region of stabilization and turn out in the region, where the amplitude grows infinitely. Accordingly, the transition to the region of instability happens stochastically. However, if the time interval, when the amplitude remains bounded, is large enough, the proposed scenario can be treated as a partial stabilization of instability.     

Filamentation instability of helicons

Nonlinear interaction of a large amplitude ducted helicon (whistler wave) with slow plasma motion is considered. The low-frequency response accounts for a finite ion gyroradius effect to the usual MHD Alfvén waves. It is found that this coupling leads to a filamentation instability which grows at a rate faster than those reported earlier.