磁层顶通量传输事件的经验重构

在地球磁层顶附近观测到的通量传输事件（Flux Transfer Event,FTE）一般被认为是瞬态局域磁重联的产物,是太阳风质量、动量和能量进入地球内磁层的重要通道.重构FTE的磁场结构可促进对其形成、演化过程及其与周围等离子体环境相互作用的理解.Grad-Shafranov重构法和磁通量绳拟合法等传统磁场重构方法适用于满足特定物理条件的磁场结构.基于平面线性插值原理,设计了一种不受具体物理条件限定的二维FTE磁场结构重构法.模型测试以及对THEMIS和Cluster卫星簇分别观测到的两个FTE的实际应用表明,在合适的多卫星位形条件下,该方法能快速有效重构出FTE的磁场空间分布,有助于推测FTE的磁场线位形,理解卫星测量数据的时间变化,以及分析等离子体物理量相对于FTE的磁场空间分布特征.      

质子地磁垂直截止刚度在2004年11月7-8日两个时刻处的数值模拟

利用单粒子轨道理论, 在T04和IGRF2000磁场模式建立的磁层模型基础上, 应用四阶龙格库塔方法, 模拟计算宇宙线带电质子在地球磁层中的运动以及沿天顶方向入射到达地球磁场内的某一特定位置, 得到了距地球表面450km高度处全球质子垂直截止刚度在2004年11月7-8日中两个时刻的计算值. 根据计算得到的684个不同位置处的截止刚度值, 分析了同一时刻地磁垂直截止刚度随磁纬和磁经的变化. 与此同时, 模拟计算了相同时刻下磁纬为30°, 磁经为0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°处, 地磁有效垂直截止刚度随高度的变化情况. 结果表明, 在磁纬30°处, 其质子有效垂直截止刚度随距离地心高度的变化沿向阳处向磁尾处方向, 变化越来越缓慢.      

火星磁层顶形成和变化的理论研究

考虑太阳风动压与行星电离层中的带电粒子热压及磁压之和平衡,建立了有大气（电离层）的行星磁层顶形成的理论模型,结合卫星对火星的观测数据,对子午面内向日侧火星磁层顶位形进行了数值计算和分析,研究了火星磁层顶位形及其与太阳风动压之间的变化关系．结果认为,火星磁层顶位形与地球磁层顶相似．太阳风动压越大,火星磁层顶越靠近火星;太阳风动压越弱,火星磁层顶越远离火星．根据火星内秉磁矩从古到今逐渐减小的观点,探索了大尺度磁场（内禀磁矩）对火星磁层顶的贡献作用,结果认为大尺度磁场越强,火星磁层顶越远离行星．这对于进一步研究火星磁层的长期演化以及其他行星磁层的位形变化都具有重要的意义．     

Galactic cosmic ray flux simulation and prediction.

A dynamic galactic cosmic ray model is proposed to quantitatively describe the z=1-28 ions and electrons of E=10-10(5) MeV/nucleon and their particle flux variations around the Earth's orbit and beyond the Earth's magnetosphere due to diverse large-scale variations of solar activity factors. The variations of large-scale heliospheric magnetic fields and the galactic cosmic ray flux variation time delays relative to solar activity variations are simulated. The lag characteristics and sunspot number predictions having been determined in detail, the model can be used to predict galactic cosmic ray flux levels.     

磁扰日向阳面对流电场转向区位置的晨昏不对称性(STARE、TRIAD、AE-C观测综合分析)

本文通过STARE观测的晨不连续性及其与TRIAD观测的场向电流分界区、AE-C卫星观测的电场转向区位置的比较,提出了在高扰日向阳面对流电场转向区位置存在着晨不对称性——晨半面所处纬度低于昏半面.该现象间接说明向阳面磁层边界层也存在某种不对称性.并在观测基础上对可造成该不对称性的物理因子进行了探讨,认为行星际磁场螺线结构对重连区位置的影响及其产生的激波结构的晨昏不对称性很可能与本文中讨论的现象有一定联系.      

磁层顶对磁层磁场的影响

太阳风与地磁场相互作用形成的磁层顶对磁层内磁场有重要影响。本文假定地磁场为偶极子,太阳风为理想导体,在太阳风与磁层的边界上满足磁场法向分量为零的边界条件。采用最小二乘法求得磁层顶电流在磁层内产生的磁场的球谐系数。从计算结果可以看出磁层顶对磁层磁场的影响。结果表明,向阳面的磁场、中性点、极光区的位置与形状与实际观测比较接近;磁尾磁场与实际观测相差较远,原因是没有加上磁尾片电流。文中还给出了太阳风与地磁轴交不同角度时的磁层磁场的计算结果。      

The accuracy of present models of the high altitude polar magnetosphere

The Polar satellite has explored the high-latitude, high-latitude magnetosphere out to 9 Earth radii (Re). The magnetic field data returned from this mission can be used both to provide data for new empirical models and to test existing models. Tests include comparing the observed location of the polar cusp with its position in the empirical models and comparing the strength of the magnetic field in the surrounding region. Near the cusp the magnetosphere is quite sensitive to solar wind conditions. In particular the energy density of the cusp plasma depends on the pressure of the solar wind applied to the interface of the cusp and the sheath. The applied pressure in turn depends on the shape of the magnetopause and the orientation of that interface, both controlled by the direction of the interplanetary magnetic field. Magnetohydrodynamic (MHD) models provide a coarse picture of the magnetosphere at high latitudes. While generally quite realistic, these too require testing against observations because even the MHD models must make some simplifying assumptions.     

行星际激波导致的磁尾等离子片中ULF波动事件

磁层中的超低频（ULF）波动在太阳风和磁层之间的能量输运过程中具有重要作用.ULF波动主要发生在内磁层,且内磁层中ULF波动影响粒子的加速及沉降,而在夜侧磁层尤其是磁尾等离子片中观测到的ULF波动比较少.基于中国自主磁层探测卫星TC-1的观测数据,发现了两例行星际激波导致的磁尾中心等离子片中ULF波动事件,并发现这两例ULF事例都包含很强的环向模驻波分量,与以往THEMIS卫星报道的同类事件观测特征相符.根据ULF波的观测特征,分析了这两例ULF波动的可能触发机制.研究结果有助于深入理解磁层对行星际激波的全球响应.      

The Physical Foundation of Forecasting Disturbances in the Geospace From Solar Disk Characteristics

The five main types of antisunward propagating energetic fluxes (particles and emission) may be thought of as well established to date, the effects of which lead to a particilar character of disturbance in the near-terrestrial environment (the Earth's magnetosphere, ionosphere and atmosphere). The strongest global restructuring of the magnetosphere and ionosphere is caused by fluxes of relatively dense n of 1-70 cm-3 at the Earth's orbit) Solar Wind (SW) quasi-neutral, low-energy (E ＜ 10 keV) plasma which cause magnetospheric and ionospheric storms lasting 24 hours or longer. For that reason, main attention is given to their study at the initial stage of research. The physical essence of the method of predicting disturbances in the near-terrestrial space environment, the amplitude of which can be expressed in, for example, the Kp index units, involves:(1) identifying all the most geo-effective SW streams of type, (2) determing their sources on the solar disk,and (3) quantifying the correlations between the characteristics of their solar sources with a maximum value of the Kp-index that is caused by the concerned type of SW stream. Semi-phenomenological relations have been obtained, which relate parameters of type SW stream sources to characteristics of geomagnetic storms:storm commencement, the time at which the storm intensity reaches its maximum values, the storm duration,as well as to the storm amplitude expressed in terms of geomagnetic indeces.      

电离层等效电流体系对行星际激波的响应研究

行星际激波是导致地球磁层-电离层系统发生扰动的重要原因之一,其可以通过对磁层-电离层系统电流体系的改变来影响地磁变化.本文采用全球三维磁流体力学数值模拟方法,分析了行星际激波作用下电离层等效电流体系的即时响应.模拟结果表明,在激波作用下伴随着异常场向电流对的产生,电离层在午前午后出现一对反向的等效电流涡.这对涡旋一边向极侧和夜侧运动,一边经历强度增强和减弱直至消失的过程.激波过后等效电流体系图像逐渐演化为激波下游行星际条件控制的典型图像.这个响应过程与行星际激波强度有关,激波强度越强,则反向的等效电流涡旋强度越大,寿命也就越短.      

第24太阳活动周地球附近磁云与非磁云事件的统计分析

为研究第24太阳活动周中磁云（Magnetic Clouds,MC）与非磁云（Non-Magnetic Clouds,non-MC）的等离子体性质及其对空间天气的影响,使用1AU处的观测数据对2008-2015年168个ICME事件进行统计与分析,其中认证出磁云事件68个,占总数的40.48%.通过分析磁云与非磁云等离子体参数对空间天气环境的影响及与太阳活动的关系,整体性质的对比及在第23和24太阳活动周中性质的对比,可以发现:在第24太阳周中,磁云引起的磁暴强度普遍大于非磁云,南北向磁场分量是引起磁暴的重要参数;磁云数和太阳黑子数有很好的相关性,非磁云数与行星际日冕物质抛射总数及黑子数的相关性稍弱,磁云数在太阳周的不同阶段表现出不同的分布特性;磁云的磁场强度和南向磁场分量整体强于非磁云,两者质子温度、密度等参数差异不大.第24周磁云事件引起的地磁效应整体上弱于第23周磁云事件,这与第24周磁云事件最大南向磁场分量、传播速度以及质子温度整体小于第23周磁云事件有关.      

基于对抗神经网络有限角度的磁层边界CT重构技术

对地球磁层进行软X射线成像探测是近年来磁层研究的前沿方向.由二维X射线成像图重构三维磁层边界的方法研究是与成像探测相关的重要研究课题.传统的计算机断层成像技术（CT）重构方法在图像数据很少时无法得到较好的重构结果,甚至无法重构三维结构.考虑到地球磁层空间分布范围方面的约束,当前卫星任务的轨道设计很难满足扫描角度的全方位覆盖,只能从有限角度观测磁层,这给磁层的CT重构带来困难.作为三维重构研究的基础,本文考查简化的二维磁层结构重构方法,采用基于对抗神经网络的CT技术对简化的地球磁层边界结构进行重构.首先使用改进的生成式对抗网络（GAN）对有限角度的卫星扫描图像进行图像补全,进而使用代数迭代重建方法（ART）重构磁层.实验表明,当扫描角度大于90°时,生成式对抗网络能有效准确地补全缺失图像,重构效果较好.      

磁层顶的Kelvin-Helmholtz不稳定性(III)可压缩不稳定波的能量和动量输运

本文在假定磁层顶为切向间断面的近似下分析了可压缩K-H不稳定波在磁层顶两侧的能量分配及能量和动量输运,讨论了相应的物理机制.计算表明,K-H不稳定性确实能在太阳风-磁层耦合中起重要作用.      

Laboratory experiments and space phenomena

Two types of convection were observed in the laboratory model of the magnetosphere: viscous convection and convection due to field lines common to both the magnetosphere and artificial solar wind. With a southward field component in the solar wind, convection from the Sun is observed in the polar cap, while with a large northward component, convection is directed toward the Sun. Merging of the field lines occurs in the cleft. With the southward component, a visor appears in front of the magnetosphere boundary. The decay of the visor into small magnetic structure is observed. The formation of an induced magnetosphere with a magnetic tail is shown in the experiments of the simulated conditions near non-magnetic bodies with a plasma shell (Venus, comets). A combined induced-intrinsic magnetosphere also was investigated.     

地球磁尾的电场模式

地球磁层中的电场是磁层等离子体运动的主要驱动力。目前常用的磁层电场为均匀晨昏电场和投影电场。本文假定磁力线为电场的等位线，地球电离层电场看做磁层电场沿磁力线在电离层的投影。利用Tsyganenko磁场模式（T89），沿磁力线反电离层电场投影到磁尾，得到了一个新的磁层电场模式。文中对偶极磁场和T89磁场模式下的投影场作了比较，说明本模式突破了偶极磁场的局限，在磁层有更大的适用范围。     

磁层电场仪前端信号处理电路研究

针对磁层稀薄等离子体环境中的电场测量,设计了一种电场仪前端信号处理电路方案.双探针电场仪通过向等离子体输出驱动电流,测量两探针间的电位差,从而测量空间电场的探测仪器.在磁层稀薄等离子体环境下,等离子体阻抗较高,电场仪探针将工作在较高的工作电压上.若探针电压接近或超过电路耐压值,则可能会影响探测结果,甚至损坏电场仪.本文结合低偏置电流的电压跟随方案和反馈悬浮电源控制方案,解决了稀薄等离子体环境中电场测量的弱电流采样和高动态电位处理问题,并采用低噪声元件和特殊电路设计,控制电路噪声.测试结果显示,本方案可使探针适应±100V的悬浮电位,实现150kHz带宽的电场信号测量,且噪声小于14nV·mHz-1/2,满足目前空间电场仪测量精度需求.      

Current sheet with medium scale developed turbulence and the formation of the plasma sheet of Earth''s magnetosphere and solar prominences

A current sheet model with developed medium scale turbulence has been constructed. It is suggested that regular plasma flow in the current sheet is compensated by diffusive flux and plasma mixing, leading to temperature equalization. The analyzed turbulence has the form of electrostatic vortices in which electrons and ions move with the same velocities and hence does not lead to anomalous resistivity and current dissipation. It is possible to determine the plasma pressure dependence on magnetic vector potential and to find the Grad—Shafranov equation solutions. The theory is used to explain the Earth's magnetosphere plasma sheet characteristics. It is taken into account that experimentally observed plasma velocity fluctuations in the Earth's plasma sheet and quiescent prominences are much higher than regular plasma flow velocities. The analysis of turbulent current sheet dynamics after the regular motion weakening allows to construct the prominence formation theory. The decreasing of plasma pressure in the sheet due to diffusion leads to field-aligned plasma flow and plasma tube filling by cold chromospheric plasma by the action of siphon mechanism.     

中性原子成像探测的物理设计与仿真

研究了磁层-电离层-热层耦合星座(MIT)卫星计划中高能中性原子成像仪(NAIS-H)探测方案的原理设计和模拟仿真. 以双星中性原子成像仪设计思想为基础,依据MIT卫星计划的总体科学目标和磁层卫星的轨道环境及相应自旋姿态,给出中性原子成像仪的技术架构,并针对地磁偶极场的环电流模型进行了模拟仿真. 仿真结果表明,所研制的NAIS-H以其高时空分辨能力适用于监测和反演磁暴期间磁层等离子体的全球动力学过程.      

Plasma convection model and generation of longitudinal currents in the earth's magnetosphere

The aim of this paper is to investigate processes in the magnetosphere and in particular the problems of the interaction of the solar wind with the Earth's magnetic field to produce large-scale convection, electric fields and longitudinal currents in the magnetosphere. The investigation is carried out in the frame of magnetic hydrodynamics. The reason for such an approach can be found in /1/. When calculating the transfer coefficients, the Böhm approximation is used, i.e. it is considered that the plasma in the near-equatorial part of the magnetosphere (quasiplanar geometry is used in the problem for simplification) is sufficiently turbulent that the condition ωτ ≈ 1 is valid (ω is the Larmor frequency of electrons, τ is effective time between two Quasi-collisions). The main subjects of investigation in this paper are the input near the equatorial boundary layer and the plasma layer of the magnetosphere tail.