三维试验粒子轨道法在磁层粒子全球输运中的应用

根据磁层粒子动力学理论, 通过偶极磁场模型验证利用三维试验粒子轨道方法模拟近地球区(r < 8R_e)带电粒子运动特征的可靠性. 在此基础上, 以太阳风和磁层相互作用的全球MHD模拟结果为背景, 利用三维试验粒子轨道方法, 对非磁暴期间南向行星际磁场背景下太阳风离子注入磁层的情形进行数值模拟, 并对北向行星际磁场背景下太阳风离子注入极尖区以及内磁层的几种不同情形进行了单粒子模拟. 模拟结果反映了南向和北向行星际磁场离子向磁层的几种典型输入过程, 揭示出行星际磁场南向时太阳风粒子在磁层内密度分布的晨昏不对称性以及其在磁鞘和磁层内的大致分布, 并得出统计规律. 模拟结果与理论预测和观测结论相一致, 且通过数值模拟发现, 行星际磁场北向时靠近极尖区附近形成的非典型磁镜结构对于能量粒子经由极尖区注入环电流区域过程有重要的影响和作用.      

极端太阳风条件下的磁层顶位形

基于极端太阳风条件下的三维MHD数值模拟数据, 构建了一种极端太阳风条件下的三维非对称磁层顶位形模型. 所提出的模型考虑了行星际南向磁场(IMF) B_z日下点距离侵蚀的饱和效应, 太阳风动压B_d对磁层顶张角影响的饱和效应, 赤道面、昼夜子午面磁层顶的不对称性以及极尖区的内凹结构和内凹中心的移动, 并利用Levenberg-Marquart多参量非线性拟合方法拟合了模型参数. 数值模拟研究表明, 在极端太阳风条件下, 随B_d增大, 磁层顶日下点距离减小, 磁层顶磁尾张角几乎不变; 随南向(IMF)B_z增大, 磁层顶日下点距离略有减小, 磁层顶磁尾张角减小, 极尖区内凹中心向低纬移动. 通过对2010年8月1日太阳风暴事件验证发现, 本文所建立的模型能够描述极端太阳风条件下的三维磁层顶位形.      

火星空间磁场结构特征

在火星空间模拟的单流体MHD模型的基础上, 研究了火星空间磁场结构及火星表面局部磁异常对磁场结构的影响. 在太阳风与火星相互作用的过程中, 形成弓激波和磁堆积区, 行星际磁场弯曲并向两极移动且被拖拽变形, 大部分磁力线从火星两极绕过, 通过火星之后在磁尾留下V字形结构. 火星表面附近局部磁异常也对火星磁场结构产生不可忽视的影响. 不同位置和强度的磁异常与太阳风相互作用形成结构及形态各异的微磁层, 如被拖拽的微磁层和存在开磁力线的微磁层等. 局部磁异常改变了近火磁场结构, 并可能改变等离子体的分布.      

太阳风向磁层输入电磁能量研究

利用全球磁流体力学（MHD）模拟结果,通过确立包含磁层顶的太阳风流线内边界来识别三维磁层顶位形,并以极尖区位置作为磁层顶日侧与夜侧的分界线,在此基础上定量研究了不同条件下穿过磁层顶向磁层内输入的电磁能量. 研究发现,磁层顶的能量传输与太阳风条件密切相关,磁重联是控制电磁能量传输的重要机制. 结果表明,当IMF（行星际磁场）南向时,极尖区后方的磁尾附近存在电磁能输入最大值,当IMF北向时,电磁能输入最大值发生在极尖区附近;南向IMF条件下,在IMF强度增大或太阳风密度增大时,磁层顶电磁能传输的电磁能量比北向IMF条件时增加更显著. 太阳风通过调节磁层顶面积间接影响到磁层顶能量传输大小. 研究还发现,北向IMF与南向IMF条件下穿过磁层顶的电磁能输入的比值范围约为10%～30%,此比值一定程度上反映了北、南方向IMF与地磁场磁重联效率的比值.      

多种观测数据驱动的三维行星际太阳风MHD模拟

三维磁流体力学（MHD）数值模拟是行星际太阳风研究的重要手段.本文发展了一种由多种观测数据驱动的三维行星际太阳风MHD数值模型.模型的计算区域为0.1AU到1AU附近，使用Lax-Friedrich差分格式在六片网格系统中进行数值求解.边界条件中磁场使用GONG台站观测的光球磁图外推获得，密度通过LASCO观测的白光偏振亮度反演得到，速度根据以上两种观测数据并利用一种基于人工神经网络技术（ANN）的方法得到，温度通过自洽方法根据磁场和密度导出.利用该模型模拟了第2062卡灵顿周（CR2062）时期的行星际太阳风，模拟结果显示出丰富的观测特征，并与OMNI以及Ulysses的实际观测值符合得较好.该模型可用于提供接近真实的行星际太阳风，有助于提高空间天气预报的精度.      

高速太阳风条件下日侧磁层顶磁通量传输事件的全球磁流体力学模拟结果

利用全球磁流体力学模拟,研究了高速太阳风条件下日侧磁层顶的磁通量传输事件（FTE）发生率的空间分布.从模拟结果中得到了FTE信号,并且这些FTE信号的特征与观测结果基本一致.磁层顶上的10个取样点共观测到39个FTE信号.统计分析表明,越靠近翼侧则观测到的FTE信号越少.这一现象可能是磁鞘中太阳风速度分布差异导致的.      

能量粒子进入磁层的数值模拟研究

来自行星际的能量粒子进入磁层的过程一直是磁层研究的热点,也是空间天气研究关注的焦点之一,而以往的工作大都集中在讨论不同行星际条件下粒子进入磁层的统计规律.本文在T89磁层模式的基础上,建立了太阳能量粒子进入磁层运动的程序,计算了几种不同能量的质子从不同方位角入射到磁层的运动轨迹.模拟结果表明,能量粒子沿着磁力线方向才可能穿越磁层到达地球表面,越偏离这个方向,则越早被反弹.能量越高的粒子进入到地球磁层上空的角度范围越大,但仍然只有沿着磁力线入射的粒子才能到达地球表面.这些结果与理论预言是一致的.      

中国地球空间双星探测计划科学研讨会召开

中国地球空间双星探测计划科学研讨会于2002年9月2至7日在山东省潍坊市举行.参加会议的有来自国家航天局、国家自然科学基金委、中国科学院空间科学与应用研究中心、中国科学院地质与地球物理研究所、中国科学技术大学、中国科学院紫金山天文台、北京大学、武汉大学、大连理工大学、中国极地研究所、浙江大学以及潍坊学院的代表共75名.会议的主题为中国地球空间双星探测计划的关键科学问题研究.会议首先邀请有关专家学者就双星计划科学应用分系统的进展情况、目前空间物理方面的一些主要研究方向的研究现状、主要结果和发展趋势做了报告.报告内容主要集中在太阳风与磁层的相互作用、磁层亚暴和磁暴的触发机制、资源1号卫星高能粒子辐射事件及磁层与电离层耦合、亚暴期间空间电流体系、磁层粒子的来源及电离层上行     

行星际磁场时钟角与地球磁层开放磁通的关系

地球磁层开放磁通F_pc是研究磁层动力学过程的重要参数之一,其与日侧和夜侧磁尾的磁场重联具有密切关系. 日侧重联率控制稳定状态下磁层开放磁通的大小,主要受各种太阳风条件的影响. 其中,行星际磁场（IMF）的时钟角是影响日侧重联率的一个重要因素. 通过全球MHD模拟,研究了行星际磁场时钟角θ_c与地球磁层开放磁通F_pc 之间的关系. 结果表明,开放磁通F_pc随着行星际磁场时钟角 θ_c逐渐接近180°（纯南向）而逐渐增加,两者之间的关系近似为F_pc∝sin3/2（θ_c/2）. 由于表征行星际磁场与地球磁场剪切程度的θ_c影响日侧重联率,从而控制F_pc,该关系反映了二者之间的物理联系.      

IMF北向时太阳风粒子向磁层输运的试验粒子模拟研究

以ACE卫星实时观测数据驱动的全球磁流体模拟为背景场,选取2003年10月22－24日行星际磁场（IMF）持续北向的事件,使用试验粒子方法,对太阳风粒子向磁层输运的过程进行模拟研究,分析北向IMF下太阳风粒子注入磁层过程中粒子在磁层内的空间分布和时间演化特征。IMF北向期间,进入环电流区域的粒子在晨侧区域的密度大于昏侧,且晨侧的粒子分布范围更广。背阳面磁鞘中的太阳风粒子可以通过低纬边界层进入磁层,但很难通过南北侧磁层顶进入磁层。进入磁尾的太阳风粒子聚集形成冷而密的等离子体片（CDPS）,模拟中CDPS的空间分布和密度大小与观测数据符合。在IMF长时间北向期间,磁尾的粒子数量呈现随时间增长的趋势,并存在约20 min的小幅度准周期变化和约5~6 h的较大幅度的准周期变化。      

International Meridian Circle Program

The Earth is buffered from the ferocious onslaught of the solar wind by a thin layer of matter known as the atmosphere and geospace. This layer absorbs energy from irradiance and outburst from the Sun, as well as from disasters, transient phenomena and anthropogenic emissions originated from Earth. Through complicated physics, the absorbed energy changes the atmospheric and geospace state and sometimes gets re-released to power extreme events such as space weather. Taking place globally, these complicated processes cannot be understood unless they are studied globally. The Chinese scientists have proposed the International Meridian Circle Program (IMCP) to meet this demand. By operating nearly 1000 instruments encompassing all latitudes along with the 120°E-60°W longitudes, IMCP aims, for the first time, to construct comprehensive 3D data representation of the atmosphere and geospace on a global scale and empower interdisciplinary research to tackle key questions related to Earth's environment and climate change.      

Recent Advances in Observation and Research of the Chinese Meridian Project

The Chinese Meridian Space Weather Monitoring Project (Meridian Project) is a ground-based geospace monitoring chain in China. It consists of 15 ground-based observation stations located roughly along 120°E longitude and 30°N latitude. In recent two years, using data from the Meridian Project, significant progress has been made in space weather and space physics research. These advances are mainly in four aspects:regional characteristics of space environment above China or along 120°E meridian line, coupling between space spheres at different heights and different physical processes, space weather disturbance and its propagation along the meridian chain, and space weather effects on ground technical facilities.      

Transient effects of solar energetic particle flux enhancements on the inner magnetosphere of the earth

In one type of space weather, the sun emits intermittent enhancements of solar energetic particle (SEP) fluxes. A fraction of these fluxes that reach the envelope of geospace can be injected into the magnetospheric particle confinement region after transiting the geomagnetic tail domain, the polar cleft/cusp region, or directly through the front side magnetopause. Common for these processes is that they provide inward diffusive “leakage” whenever the immediate external flux environment is more intense than in the outer trapping region. Conversely, following injection events outward leakage can also occur whereby the confinement region becomes a source of Magnetosheath particles. Numerical modeling has been carried out to investigate the effects on the ambient fluxes in the Earth's radiation belts from this effect.     

上行离子源区卫星探测的轨道需求分析

极区从电离层到磁层的上行粒子流探测研究是空间天气建模中的重要问题,其起源和加速机制是磁层-电离层-热层耦合小卫星星座计划的主要科学目标. 磁层-电离层-热层耦合小卫星星座计划拟定由两颗磁层星和两颗电离层/热层星组成星座对极区进行联合观测. 其中,上行粒子源区附近的就位探测是电离层-热层耦合机制研究的重点,也是电离层/热层星轨道设计的关键. 根据相关空间探测计划和卫星观测结果,通过比较圆轨道和椭圆轨道两种方案,确定电离层/热层星采用椭圆轨道.      

数据同化在空间天气学中的应用

由太阳活动引起的耀斑和日冕物质抛射等短时间尺度变化的空间天气事件会影响并危害地球磁层、电离层、中高层大气、卫星运行安全以及人类健康,因此对这些空间天气事件的预测显得尤为重要。数据同化在稀疏观测和异步采集的情况下能够增加模型的预测能力,对模型变量进行自洽分析。在数值预报中引入数据同化方法,能够提高预测可信度。本文从数据同化方法的角度出发,主要分析了数据同化目前在大气、电离层、磁层、太阳及其他行星科学研究中的应用,并初步讨论了数据同化未来在空间天气方面的应用。      

KuaFu Mission

The KuaFu mission-Space Storms, Aurora and Space Weather Explorer-is an "L1+Polar" triple satellite project composed of three spacecraft: KuaFu-A will be located at L1 and have instruments to observe solar EUV and FUV emissions, and white-light Coronal Mass Ejections (CMEs), and to measure radio waves, the local plasma and magnetic field,and high-energy particles. KuaFuB1 and KuaFu- B2 will bein polar orbits chosen to facilitate continuous 24 hours a day observation of the north polar Aurora Oval. The KuaFu mission is designed to observe the complete chain of disturbances from the solar atmosphere to geospace, including solar flares, CMEs, interplanetary clouds, shock waves, and their geo-effects, such as magnetospheric sub-storms and magnetic storms, and auroral activities. The mission may start at the next solar maximum (launch in about 2012), and with an initial mission lifetime of two to three years. KuaFu data will be used for the scientific study of space weather phenomena, and will be used for space weather monitoring and forecast purposes. The overall mission design, instrument complement, and incorporation of recent technologies will target new fundamental science, advance our understanding of the physical processes underlying space weather, and raise the standard of end-to-end monitoring of the Sun-Earth system.     

Real-time global MHD simulation of the solar wind interaction with the earth’s magnetosphere

We have developed a real-time global MHD (magnetohydrodynamics) simulation of the solar wind interaction with the earth’s magnetosphere. By adopting the real-time solar wind parameters and interplanetary magnetic field (IMF) observed routinely by the ACE (Advanced Composition Explorer) spacecraft, responses of the magnetosphere are calculated with MHD code. The simulation is carried out routinely on the super computer system at National Institute of Information and Communications Technology (NICT), Japan. The visualized images of the magnetic field lines around the earth, pressure distribution on the meridian plane, and the conductivity of the polar ionosphere, can be referred to on the web site (http://www2.nict.go.jp/y/y223/simulation/realtime/).The results show that various magnetospheric activities are almost reproduced qualitatively. They also give us information how geomagnetic disturbances develop in the magnetosphere in relation with the ionosphere. From the viewpoint of space weather, the real-time simulation helps us to understand the whole image in the current condition of the magnetosphere. To evaluate the simulation results, we compare the AE indices derived from the simulation and observations. The simulation and observation agree well for quiet days and isolated substorm cases in general.     

ULF wave index as magnetospheric and space-weather parameters

Waves in the Ultra Low Frequency (ULF) band owe their existence to solar wind turbulence and transport momentum and energy from the solar wind to the magnetosphere and farther down. Therefore an index based on ULF wave power could better characterize solar wind–magnetosphere interaction than K_P, Dst, AE, etc. indices which described mainly quasi-study state condition of the system. We have shown that the ULF wave index accurately characterize relativistic electron dynamics in the magnetosphere as these waves are closely associated with circulation, diffusion and energization of relativistic electrons in the magnetosphere. High speed solar wind streams also act as a significant driver of activity in the Earth’s magnetosphere co-rotating interaction region and are responsible for geomagnetic activities. In the present paper, we have analyzed various cases related with very weak (quiet) days, weak days, storm days and eclipse events and discussed the utility of the ULF wave index to explain the magnetospheric dynamics and associated properties. We have tried to explain that the ULF wave index can equally be useful as a space weather parameter like the other indices.