Interchange instability as a mechanism of magnetotail current disruption at the magnetic storm recovery phase

The theory of relaxation of geomagnetic depression observed during magnetic storm has been proposed based on the knowledge of the interaction between the Dst index and the magnetotail current. It has been indicated that the disruption of the tail current that was enhanced during the storm main phase can be caused by the interchange instability, which develops in the boundary plasma sheet due to the sheet curvature in the near to the Earth region and due to a sharp, directed toward the curvature center, plasma pressure gradient at the boundary between the plasma sheet and the tail lobe. The dispersion equation and expression for the instability growth rate have been obtained. The theoretically predicted characteristic time of storm depression relaxation τ is ～10 h and is in good agreement with the experimental estimate.     

大功率高频电波加热电离层中参量衰减不稳定性研究(1):数值模拟

参量衰减不稳定性(Parametric Decay Instability,PDI)在大功率高频(High frequency,HF)电波与电离层等离子体相互作用的过程中扮演着十分重要的角色,本文采用广义Zakharov方法对常规的等离子体流体力学方程组进行相应处理后,并在近似实际的电离层背景和电波传播模型下,构建了高频电波加热电离层激发PDI的数值计算模型.模拟结果发现:在毫秒量级的时间尺度上,大功率高频电波在寻常波(Ordinary wave,O波)反射点高度附近激发出了朗缪尔波(Langmuir wave)和离子声波(Ion-Acoustic wave)两种等离子体静电波模,模拟中产生的朗缪尔波和离子声波相应波数为5~11rad·m~(-1),结果与利用色散关系求出的理论值4~7 rad·m~(-1)近似一致,密度扰动幅值从10~6m~(-3)量级指数级增长到了10~(10)m~(-3)量级,直至能显著影响与"低频"密度背景相关的等离子体频率后,出现了等离子体"空穴"结构以及朗缪尔波被"俘获"现象,在扰动空间内的小尺度静电场幅值最高能达到100 V·m~(-1)量级,最终造成一种强烈的局地化"空穴"湍流现象.本文的研究有助于深入理解PDI的物理机制,对研究大功率高频电波与电离层等离子体之间复杂的非线性相互作用也有着非常重要的意义.     

Plasma disturbance sources in the postsunset low-latitude outer ionosphere according to the Intercosmos-Bulgaria-1300 satellite

The satellite low-latitude and midlatitude measurements of the disturbed postsunset plasma density and electron temperature at altitudes of ～900 km have been compared with the data of incoherent scattering and high-altitude rocket launching at the corresponding local time. It has been found that plasma density disturbances are independently caused by the turbulent interaction between atmospheric masses of gas and plasma ascending from heated and not yet cooled ionospheric regions and cooling masses descending from protonospheric altitudes. Plasma regions with an energetically nonequilibrium vertical density distribution of the mixture of heavy ion impurity (O⁺) and major light ions (H⁺) can simultaneously appear, as a result of which the gradient-drift impurity instability is generated. If this instability is sufficiently developed, there appears an anomalous ion drift with the formation of real plasma regions of decreased density. All these phenomena generate different irregularities in a wide range of scales: from several tens or hundreds of meters to several hundreds of kilometers.     

Measurements of the direction of the solar wind using interplanetary scintillation

EISCAT observations of the interplanetary scintillation of a single source were made over an extended period of time, during which the orientation of the baselines between the two observing sites changed significantly. Assuming that maximum correlation between the scintillations observed at the two sites occurs when the projected baseline is parallel to the direction of plasma flow, this technique can be used to make a unique determination of the direction of the solar wind. In the past it has usually been assumed that the plasma flow is radial, but measurements of eleven sources using this technique have indicated conclusively that in at least six cases observed at mid or high heliocentric latitude there is a significant non-radial component directed in four cases towards the heliocentric equator and in two cases towards the pole.     

Formation of strong stationary vortex turbulence in the terrestrial magnetosheath

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.     

Asymmetry of nonlinear interactions of solar MHD discontinuities with the bow shock

Oblique interaction between the solar fast shock wave, which is a typical nonstationary strong discontinuity in the interplanetary space, and the bow shock front upstream of an Earth-type planetary magnetosphere is studied. Attention has been paid to the qualitative and quantitative (with respect to the proton density distribution) dawn-dusk (or morning-evening) asymmetry of the discontinuities refracted into the magnetosheath, which originates in the ecliptic plane on different sides of the Sun-Earth line. The results under discussion have been corroborated experimentally by the gas-kinetic pattern of the bow-shock front and the WIND and ISEE 3 spacecraft measurements of the plasma density.     

Interplanetary scintillation observations of interaction regions in the solar wind

Co-rotating interaction regions (CIRs) between fast and slow streams of plasma are a prominent feature of the solar wind. Measurements of interplanetary scintillation (IPS) using the three widely separated antennas of the EISCAT facility have been used to detect the compression regions at the leading edges of interaction regions and to determine the location and velocity of the structure. Observations show that interaction regions have developed as close to the Sun as 25–30 solar radii, a result supported by theoretical modelling which shows that the conditions needed for CIRs to develop exist inside 30 solar radii.     

The association between giant pulsations (Pgs) and the auroral oval

Two features of giant pulsations (Pgs) which still require an explanation are firstly, why Pgs occur mainly in the early morning sector (i.e. 03:00-07:00 MLT) and not at other times of day, and secondly, why Pgs occur preferentially in a narrow latitudinal band (approximately 63○-68○ geomagnetic latitude). Using statistics from 34 Pg events observed by the EISCAT magnetometer cross, a comparison has been made between the location of the Pg resonant field lines and the equatorward edge of the auroral oval. The majority of these Pg events appear to occur just poleward of this boundary. Using these results, an explanation of the two features of Pgs as detailed above is made. This explanation involves the interaction of protons, which may be responsible for the Pg events, with the inner edge of the plasma sheet or with its ionospheric equivalent, the equatorward edge of the auroral oval.     

INTERACTION BETWEEN AIRGUNS*

In the design of linear airgun arrays the interaction between the airguns is usually neglected. We review the different formulae which have been proposed for the minimum separation between airguns at which the interaction is negligible. These formulae can all be approximated by a linear function of a single variable. We have analyzed a large number of measurements in order to establish the amount of interaction between two airguns of various volumes at different pressures and depths. The resulting far-field signature has been measured and compared with the sum of the signatures from the two airguns measured in the same experimental situation. The changes in primary pulse amplitude, bubble period and primary/bubble peak-to-peak amplitude ratio were computed from the measurement data as a function of airgun separation, chamber volume, chamber pressure and airgun depth. The influence of a waveshape kit was investigated, and the effects of interaction and the effects of using a waveshape kit were compared.     

Gel- and ultramembrane filtration of aquatic humus: A comparison of the two methods

Fractionation is considered to be a necessary approach in order to obtain information about the complex composition of aquatic humus. Gel filtration has been used for this purpose for the last decade and recently ultramembrane filtration has been found useful. The two techniques are briefly described and results of a combined use of the two methods reported. The results show a poor correspondence, with regard to molecular size, between the two methods. Due to uncontrollable interaction between the gel used (Sephadex) and humus, the ultramembrane filtration technique is considered to be preferable for desalting and molecular size fractionation of aquatic humus.     

A method for assessing kinematic bending moments at the pile head

The conventional design methods for seismically loaded piles still concentrate in providing adequate resistance from the pile to withstand only the inertial bending moments generated from the oscillation of the superstructure, thus neglecting the effect of kinematic interaction between pile and soil. By contrast there has been extensive research on kinematic effects induced by earthquakes and a number of simplified methods are available for a preliminary evaluation of kinematic bending moments at the interface between two soil layers. Less attention has been paid to the effects of kinematic interaction at the pile‐head. The paper summarizes recent research work on kinematic response analysis of fixed‐head piles aimed at the performance evaluation of a piled foundation. Results from an extensive parametric study, undertaken by means of three‐dimensional FE analyses, suggest a new criterion to predict kinematic bending effects at the pile head, where the combination of kinematic and inertial effect may be critical. Copyright © 2010 John Wiley & Sons, Ltd.     

激波在磁盔－电流片位场中的传播：（Ⅰ）激波与磁盔间的相互作用

利用新近获得的子午面磁盔－电流片背景太阳风稳态解，对激波从盔底沿电流片方向往外传播时与磁盔间的相互作用进行了数值模拟研究，重要新结果是：１．磁盔的存在使受扰介质速度跃变中央出现下凹，随着激波传出磁盔区并沿电流片方向传播，速度下凹逐渐减弱以致消失；２．激波将磁盔拉长并把盔顶的环形（垂直赤道面）磁场带到行星际空间，成为行星际磁场南向分量的来源之一；３．５个太阳半径（Ｒ⊙）内的磁盔部分将出现精细结构，沿盔外边界形成两条高速带，以及马蹄形密度（亮）环形结构等．这些结果表明，太阳附近高速等离子体与磁盔间存在重要的动力学相互作用过程，对行星际空间的太阳风三维结构有重要影响．     

激波在磁盔－电流片位场中的传播：（Ⅰ）激波与磁盔间的相互作用

利用新近获得的子午面磁盔－电流片背景太阳风稳态解，对激波从盔底沿电流片方向往外传播时与磁盔间的相互作用进行了数值模拟研究，重要新结果是：１．磁盔的存在使受扰介质速度跃变中央出现下凹，随着激波传出磁盔区并沿电流片方向传播，速度下凹逐渐减弱以致消失；２．激波将磁盔拉长并把盔顶的环形（垂直赤道面）磁场带到行星际空间，成为行星际磁场南向分量的来源之一；３．５个太阳半径（Ｒ⊙）内的磁盔部分将出现精细结构，沿盔外边界形成两条高速带，以及马蹄形密度（亮）环形结构等．这些结果表明，太阳附近高速等离子体与磁盔间存在重要的动力学相互作用过程，对行星际空间的太阳风三维结构有重要影响．     

K-H不稳定性在多电流片系统磁场重联中的效应

等离子体系统中存在两个或多个电流片时，电流片中发生的不稳定性可能会相互作用．行星际磁场北向时，背阳面碰层顶电流片与磁尾等离子体片之间可能发生相互作用，高纬边界层强烈的流场剪切可能促进磁场重联，产生磁层亚暴．本文运用二维可压缩磁流体模拟研究具有强流场剪切的多个电流片系统中磁场重联的演化．结果表明，Kelvin－Helmholtz不稳定性使多电流片系统的磁场重联过程明显加快；相邻电流片之间的距离越近，两者相互作用越强，重联增长率越大；在三电流片系统中，超Alfven速度强流场导致外侧两个电流片中出现强烈的磁场重联，并引发中心电流片的磁场重联．行星际磁场北向时，也可能发生磁层亚暴．     

Interaction between parallel Gaussian electromagnetic beams in the ionosphere

In this paper, the propagation of two initially (z=0) parallel Gaussian electromagnetic beams, propagating in the z-direction in ionosphere, has been investigated. The nonlinearity in the dielectric function, responsible for the interaction between the beams arises from the redistribution of the electron density, caused by the nonuniform distribution of electron temperature determined by the Ohmic heating of the electrons and the energy loss of electrons on account of collisions. The wave frequencies have been assumed to be much larger than the electron collision frequency and gyrofrequency. A self-consistent solution of the electromagnetic wave equation and energy balance equation (considering the solar radiation) has been obtained in the paraxial approximation. Second-order coupled ordinary differential equations have been obtained for the distance between the centers of the beams and the beam widths in the x and y directions as a function of the distance of propagation along the z-axis. Using the available database for the mid-latitude daytime ionosphere, the equations have been solved numerically for a range of parameters and a discussion of the results has been presented. The physical basis for the fact that the beams move towards each other, when the resulting irradiance distribution of the two beams has a maximum in the space between the two beams, has been highlighted.     

基于探空火箭的朗缪尔探针方案设计

为研究中国低纬电离层垂直高度的精细结构,研发了一种以探空火箭为平台朗缪尔探针,用于就位测量电离层空间等离子体的特性参数及其扰动情况.本文分析了朗缪尔探针的任务需求和目标,并在朗缪尔探针基本测量原理的基础上,对朗缪尔探针基本测量方案进行了论证分析和设计,包括传感器形状、大小和表面镀层的选取设计,双探针的设计,扫描电压和工作模式的设计,及电子学测量电路的设计.本朗缪尔探针采用两路完全相同的球形探针,两路探针同步工作,各自独立完成测量.朗缪尔探针研制完成后,分别进行了信号模拟源测试和等离子体源测试:信号模拟源测试结果显示两路探针电子学工作状态良好,对微弱电流信号的响应具有很高的线性度;在等离子体模拟装置内对电子探针整机测试的初步结果表明该载荷可以正确测量等离子体的特性参数,能够满足科学探测的需求.     

Proton interaction with quasi-electrostatic whistler mode waves in an inhomogeneous plasma (magnetosphere)

We study the interaction between energetic protons of the Earth’s radiation belts and quasi-electrostatic whistler mode waves. The nature of these waves is well known: whistler waves, which are excited in the magnetosphere due to cyclotron instability, enter the resonant regime of propagation and become quasielectrostatic, while their amplitude significantly increases. Far enough from the equator where proton gyrofrequency and transversal velocity increase the nonlinear interaction between these waves and energetic protons becomes possible. We show that plasma inhomogeneity may destroy cyclotron resonance between wave and proton on the time scale of the order of particle gyroperiod which in fact means the absence of cyclotron resonance; nevertheless, the interaction between waves and energetic particles remains nonlinear. In this case, particle dynamics in the phase space has the character of diffusion; however, the diffusion coefficients are determined by the averaged amplitude of the wave field, but not by its resonant harmonics. For real parameters of the waves and magnetospheric plasma, proton pitch-angle diffusion leading to their precipitation from the magnetosphere becomes essential.     

Inelastic seismic behavior of soil–pile raft–structure system under bi-directional ground motion

Performance based design of structure requires a reasonably accurate prediction of displacement or ductility demand. Generally, displacement demand of structure is estimated assuming fixity at base and considering base motion in one direction. In reality, ground motions occur in two orthogonal directions simultaneously resulting in bidirectional interaction in inelastic range, and soil–structure interaction (SSI) may change structural response too. Present study is an attempt to develop insight on the influence of bi-directional interaction and soil–pile raft–structure interaction for predicting the inelastic response of soil–pile raft–structure system in a more reasonably accurate manner. A recently developed hysteresis model capable to simulate biaxial interaction between deformations in two principal directions of any structural member under two orthogonal components of ground motion has been used. This study primarily shows that a considerable change may occur in inelastic demand of structures due to the combined effect of such phenomena.     

Inertial stratification of an expanding highly ionized multicomponent plasma bunch

The initial composition of a four-component plasma bunch of a high specific energy has been determined, as well as its characteristics during the process of expansion. It is shown that the interaction of particles under a high energy is of the Coulomb character and this interaction is unable to ensure the same velocity of components with different atomic masses right from the very beginning of bunch expansion, leading to their radical stratification.     

Stochastic seismic response of multiply-supported secondary systems in flexible-base structures

A formulation has been proposed for the transfer function of a secondary system response while the primary system is supported on a compliant soil and the excitation comprises of translational ground motion at its base. For this purpose, the earlier formulation of the authors for the fixed-base case, which exactly considers the interaction between the two sub-systems and is based on the use of their individual modal properties, has been extended. Also, the concept of modifying the input excitation for the interaction accelerations (associated with the soil–structure interaction) has been used. An example P–S system and three example earthquake excitations have been considered to illustrate the proposed formulation and to estimate the expected response peak amplitudes in the secondary system. This study shows that ‘detuning’ of the tuned systems may occur in case of significant soil–structure interaction. Further, for the reasons of both safety and economy, ignoring the interaction effects in designing the secondary systems may not always be justified. Copyright © 1999 John Wiley & Sons, Ltd.