不同上边界条件下的极区电离层数值模拟

利用一维自洽的极区电离层模型,研究了沿磁力线方向不同电离层-磁层耦合条件下极区电离层的响应.此模型在110-610km的电离层空间区域内,综合求解描述极区电离层的连续性方程、动量方程和能量方程,以得到电离层数值解.研究发现,上边界条件在200 km以上的高度能显著地影响电离层参量的形态.较高的O+上行速度对应较低的F层峰值和较高的电子温度.不同边界O+上行速度对应的温度高度剖面完全不同.200km以上电子温度高度剖面不但由来自磁层的热流通量所控制,同时还受到场向O+速度的影响.对利用电离层模型研究电离层内部物理过程提出了建议.      

1994年2月21日行星际激波引起的磁暴

利用Imp-8,Geotail和Goes-6等卫星资料,研究了1994年2月21日0900UT到达地球磁层的行星际激波引起的磁暴期间,从太阳风向磁层传输能量的有关问题.结果指出:（1）南向行星际磁场（IMF）的长持续时间不是太阳风向磁层输能的必要条件.南北振荡的,较强IMF也能产生显著的能量传输;（2）行星际扰动磁场通过弓激波和磁层顶后扰动磁能增加,增幅将近5倍;（3）在磁层内扰动磁场的Bz分量在1×10-4Hz附近显著被吸收.这一低频扰动磁场可能是磁暴期间导致氧离子和质子等环电流粒子向内扩散并被加速的原因之一.     

2010年4月地球同步轨道相对论电子增强事件分析

为研究2010年4月地球同步轨道相对论电子通量异常增强事件的原因, 选取了2004-2010年之间高速太阳风下7个类似事件进行对比分析. 探讨了多种可能导致此次异常事件的太阳风和地磁条件. 结果表明, 较弱的磁暴使得相对论电子高通量区域更接近同步轨道, 此外, 哨声波加速很可能在2010年4月地球同步轨道相对论电子通量异常增强事件中起到重要作用. 磁暴强度与种子电子的注入深度密切相关, 表现为Dst指数曲线的形态与能量为30～100keV的电子高通量区域的下边缘高度吻合. 能量为30～100keV电子的注入深度影响了能量大于300keV的电子出现的磁层区域. 此事件中, 由于磁暴相对较弱, 种子电子向内磁层注入的深度较浅, 更靠近同步轨道区域, 这使得相对论电子大量出现的区域也靠近同步轨道, 最终导致同步轨道相对论电子通量异常增强. 另外, 2010年4月地球同步轨道相对论电子通量异常增强事件中, 高强度的亚暴提供了充足的种子电子并加强了波粒相互作用, 这也是相对论电子增强的必要条件.      

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.      

低轨道中等能量电子对地磁扰动的响应

低轨道高度上能量电子通量变化与地磁扰动程度密切相关.利用我国资源2号(ZY-2)03星空间环境监测分系统在轨工作期间所获得的能量电子探测数据,以及美国NOAA-15,NOAA-16,NOAA-17三颗卫星中等能量电子探测器自1998年以来积累的太阳同步轨道中等能量电子探测数据,结合地磁活动观测数据,对低轨道高度上中等能量电子对地磁扰动的响应特性进行了统计分析.结果表明,该区域的中等能量电子通量在磁暴、磁层亚暴期间有显著增强,增幅大小与地磁活动程度呈正相关关系,强磁暴期间增幅可达一个数量级左右,在响应时间上存在电子通量变化滞后于磁扰的时间特性.      

极区顶部电离层离子上行的太阳活动依赖性研究

利用第23太阳活动周DMSP F12,F13和F15卫星数据,分别对南北半球极区顶部电离层离子上行的太阳活动依赖性进行了研究.结果表明,南北半球上行事件对太阳活动的响应特征基本一致,即高（低）太阳活动时,离子上行通量以及上行数密度较大（小）,但是上行速度及上行发生率较低（高）.以南半球高纬为例,计算得到离子上行通量、数密度、速度及发生率在高低太阳活动条件下的比值分别约为2.26,3.35,0.71,0.51.对离子上行太阳活动依赖性的可能原因进行了分析.不同太阳活动水平下,光致电离及高能粒子沉降的差异会导致电离层离子密度的不同,而电离层离子密度的变化会改变离子elax-elax中性大气之间的碰撞频率,这是影响离子上行发生率的一个重要原因.      

磁层-电离层电动耦合与中纬地磁指数的变化

本文探讨磁层一电离层耦合过程内中纬地磁指数的变化特点,并与极光电集流和赤道电集流(指数)变化相比较。相关分析和时序叠加分析均表明,高、中、低纬地磁指数变化可归结为磁层一电离层电动耦合的统一物理图象。有R事件的磁暴主相初期和无R事件的磁扰期内,赤道电集流和中纬地磁指数的变化各不相同。这再次证明,耦合分析中将磁层源扰动的直接穿透作用与经电离层内动力过程的效应二者加以区分和综合研究是很重要的。      

亚极光区极化流发生期间电离层离子下行的统计

亚极光区极化流是地球磁层–电离层耦合过程中最重要的现象之一,对电离层具有重要的调制作用.多数情况下,亚极光区极化流发生时会伴随局地离子上行流动,目前已对其有充分的研究,但对离子下行的研究却甚少.本文分析了DMSP卫星在2001-2015年间16个地磁暴中的观测数据,在483个亚极光区极化流事件中找到102个离子下行事件...     

太阳纯电子事件和质子-电子事件的电子能谱的机制

本文计算、分析了太阳耀斑加速电子在日冕中传输时激发的等离子体尾场的效应,认为耀斑电子的高能成份激发的尾场,能够加速低能耀斑电子,低能耀斑电子的能量增值可达几十keV至上百keV,这种尾场加速将软化约100keV以下的能量范围内(探测阈之上)的耀斑电子能谱。结合考虑尾场效应,本文提出了太阳耀斑加速电子从加速区到形成电子事件之间的能谱演化模式,说明了太阳纯电子事件的双幂律电子能谱和太阳质子-电子事件的单幂律电子能谱的形成,认为两类事件的电子能谱差异为耀斑电子日冕传输中不同程度的尾场效应所致,前者尾场效应弱,电子能谱呈双幂律,后者尾场效应较强,电子能谱为单幂律谱。      

磁层－电离层电动耦合与中纬地磁指数的变化

本文探讨磁层一电离层耦合过程内中纬地磁指数的变化特点，并与极光电集流和赤道电集流（指数）变化相比较．相关分析和时序叠加分析均表明，高、中、低纬地磁指数变化可归结为磁层一电离层电动耦合的统一物理图象．有Ｒ事件的磁暴主相初期和无Ｒ事件的磁扰期内，赤道电集流和中纬地磁指数的变化各不相同．这再次证明，耦合分析中将磁层源扰动的直接穿透作用与经电离层内动力过程的效应二者加以区分和综合研究是很重要的．     

Current carriers for the field-aligned current system

Recently the Dynamics Explorer satellites have returned a large body of data containing high resolution magnetometer measurements and distributions of charged particles of all but thermal electrons. From these data a systematic study has begun of the relations of the field-aligned currents to particle precipitation structures and the identification of the charge carriers. The data have been separated into three levels of magnetic activity and three local time sectors. Results of this study include the following:1. During very quiet periods, field-aligned currents exist primarily as fine structure.2. During onset of substorms, Region 1 and Region 2 become clearly evident but contain significant structure.3. As magnetic activity subsides, current regions become less distinct, and structure becomes more dominant.4. The distribution of the upward currents derived from magnetometer data and calculated from suprathermal electron data agree remarkably well in shape but not necessarily in magnitude.5. At all local times, >5 eV electrons seldom carry most of the upward current.6. Except for the accelerated Inverted-V electrons, the dominant upward current carriers which are measured are below 500 eV and are distributed in energy.7. Dusk upward currents (Region 1) are associated with the Boundary Plasma Sheet (BPS).8. Suprathermal electron bursts are important current carrying structures.     

Field-aligned flows of ionospheric plasma in the magnetosphere

Data are presented from occasions when one of the detectors of the Suprathermal Plasma Analyser on GEOS-2 observed along the magnetic field direction. Electrons were seen with larger fluxes along the field-aligned direction than at 80° to it. One particular class of these events was identified on the night-side when electrons in the energy range 10's to 100's eV were seen. These electrons of ionospheric origin may be associated with suprathermal electron bursts or the permanent power law population of the diffuse auroral zone.     

由高能电子引发的风云二号C星跳变事件概率分析

通过对地球同步轨道高能电子监测数据(来自GOES)与风云二号卫星跳变事件的对比分析发现, 跳变事件均发生在高能电子增强事件即所谓高能电子暴期间, 因此初步断定, 跳变事件与高能电子引起的卫星介质深层充放电事件有关. 通过对不同通量高能电子增强事件期间所发生的跳变事件发生率进行量化计算, 给出跳变事件发生概率的计算方法, 为卫星在轨运行管理及防护提供参考.      

Distribution and variability of accelerated electrons at Mars

We investigate accelerated electrons observed by Mars Global Surveyor (MGS), using data from the Electron Reflectometer (ER) instrument. We find three different types of accelerated electron events. Current sheet events occur over regions with weak or no crustal fields, have the highest electron energy fluxes, and are likely located on draped magnetotail fields. Extended events occur over regions with moderate crustal magnetic fields, and are most often observed on closed magnetic field lines. Localized events have the lowest energy fluxes, occur in strong magnetic cusp regions, and are the most likely kind of event to be found on open magnetic field lines. Some localized events have clear signatures of field-aligned currents; these events have much higher electron fluxes, and are preferentially observed on radially oriented open magnetic field lines. Electron acceleration events, especially localized events, are similar in many ways to events observed in the terrestrial auroral zone. However, physical processes related to those found in the terrestrial cusp and/or plasmasheet could also be responsible for accelerating electrons at Mars.     

超高能宇宙线电子在星际介质中的传播

本文研究能量高达1012eV以上宇宙线电子在星际介质中的传播特征, 得到了一些有趣的结果。作为一种自然的猜测, 宇宙线电子高能成份的区域性特征, 可能是导致银河系γ射线辐射的非均匀成团状分布结构的直接原因。      

Plasma transport in the plasmasphere

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.     

Characteristics of the high-latitude ionospheric particle sources: Transversely accelerated ions (TAI) at 1400 km

The auroral acceleration process that produces transversely accelerated ions is studied in detail using data primarily from a single auroral oval crossing of the ISIS-2 satellite at 1400 km. This data set is of significance because a special operational mode of the soft particle spectrometers allowed unusual temporal and pitch angle resolution to be obtained. We conclude that transversely accelerated ions having a sharp cutoff in pitch angle were accompanied by the emission of a VLF saucer and the simultaneous occurrence of an upstreaming electron beam. In contrast to the very flat pitch angle distribution of the ions, the highly field-aligned upstreaming electrons (well inside the loss cone) accompanying the ions seem to imply the existence of downward directed electric field parallel to B below 1400 km with net potentials in excess of 200 volts. The occurrence of such field-aligned electrons and VLF saucers in association with some transversely accelerated ions provides additional information on the acceleration process and reveals the complexity of the active flux tube.     

Counterstreaming hydrogen and oxygen ions observed in the magnetosphere on ISEE-1

Counterstreaming ions or ions travelling simultaneously both parallel and antiparallel to the magnetic field direction have been briefly noted in the literature but have not been studied previously in depth. We have studied over 60 counterstreaming ion (CSI) events observed on the ISEE-1 satellite. They were found to occur at altitudes of about 2 to 8 Earth radii on L shells of about 5 to 12 in the evening-to-morning sector from about 1700 - 0900 LT. Often both oxygen and hydrogen ions at a number of energy levels are counterstreaming but some events show only either oxygen or hydrogen ions involved. One particularly interesting event shows only counterstreaming oxygen ions with 417 eV energy; oxygen ions of lower energy (215 eV) and above (630–17000 eV) and all the hydrogen ions between 215–17000 eV energy have lower fluxes and/or nearly isotropic pitch angle distributions. This event correlates well with wave activity in the 17–100 Hz band and is also accompanied by 200 eV downgoing and 400 eV upgoing electrons. Details of this event and the other counterstreaming events are presented.     

FY-3A卫星与NOAA系列卫星高能带电粒子实测结果的比较

FY-3A卫星是运行于830 km高度的太阳同步轨道气象卫星, 其搭载的空间环境监测器可观测3~300 MeV的高能质子和0.15~5.70 MeV的高能电子. FY-3A卫星在轨工作期间, 太阳活动处于由谷年向峰年过渡期, 空间环境非常平静, 探测结果显示3~300 MeV的高能质子分布主要集中在南大西洋辐射带异常区, 0.15~5.70 MeV的高能电子分布区域除南大西洋异常区外, 还分布在南北两极高纬区域. FY-3A与NOAA卫星测量结果反映出带电粒子强度及分布区域随投掷角变化的空间各向异性特征. 本文在充分考虑了带电粒子时间、空间分布差异以及比对探测器之间自身设计差异的前提下, 经过归一化处理后, 首次对两颗卫星同期探测结果进行相关性分析, 验证了两颗卫星相同时空条件下高能带电粒子通量分布的一致性; 说明FY-3A空间环境监测器不仅具备空间带电粒子辐射监测能力, 且探测结果有效可靠, 可用作辐射带环境数据源的组成部分, 为发展新的模型, 深入研究辐射带高能粒子的分布、起源和传输等提供新的观测依据.