地球极区电离层对行星际激波的响应

本文就地球电离层对行星际激波的动力学响应进行三维全球数值模拟研究．背景行星际磁场为螺旋场，南北分量为零；初始电离层由Ⅰ区场向电流和相应的晨昏电场所主导；行星际激波沿日地连线方向撞击地球．模拟结果表明，在激波的作用下，电离层Ⅰ区电流系统向子夜方向运动，在向阳侧相继出现与原Ⅰ区电流反向的异常场向电流对和同向的新生Ⅰ区电流对．该异常场向电流对在极盖区形成瞬间昏晨电场，尾随原Ⅰ区电流向夜侧方向漂移直至湮没．与此同时，新生的Ⅰ区电流不断增强并向夜侧和赤道方向延伸，最终取代原Ⅰ区电流，相应极盖区又恢复到原来的晨昏电场状态．这一响应过程和行星际激波强度有关：激波强度越强，新生的Ⅰ区场向电流也越强，它向赤道方向延伸的距离也越大，能到达的纬度也越低．上述结果在趋势上与观测到的输运对流涡旋和亚极光块的运动特征一致．     

极光电激流的地方时和季节变化特性研究:CHAMP卫星观测

极光电激流是极区电流系的重要组成部分.本文利用CHAMP卫星10年的高精度标量磁场数据研究了极光电激流的地方时和季节变化特征,并对卫星与地面台站观测到的极光电激流进行了对比分析.结果表明,日侧极光电激流主要受太阳辐射的影响,而夜侧极光电激流主要受亚暴的影响.极光电激流具有明显的年、半年变化特征.夏季东向电激流和日侧西向电激流强于冬季,而夜间西向电激流冬季强于夏季.东向电激流和日侧的西向电激流在两至点增强,夜侧的西向电激流则在两分点增强.西向电激流与AL、SML指数有较好的相关性,东向电激流与SMU指数有较好的相关性,而与AU指数有一定差异,这与地磁台站的有效探测范围有关.     

地球磁层里磁泡的跨尾尺度研究

爆发流(Busty Bulk Flows)事件是发生在地球磁层里的等离子体输运现象,磁泡模型能很好地解释这一过程.现有的理论和观测事实已给出了对磁泡在跨尾方向上的尺度以及其他重要的物理参数的估计,但由于观测手段的限制这些参数并不十分精确,而只是个数值域.本文从最新的Tsyganenko磁层模型出发,利用磁泡在极光区根部的位置参数和自编的磁力线跟踪程序,通过映射给出了对应的磁泡在磁赤道面跨尾方向上的尺度.计算结果与理论预计和观测事实相符.     

基于ARTEMIS卫星数据的月球轨道附近地球弓激波位型研究

地球弓激波是超音速太阳风和地球磁层相互作用的产物,以往由于数据所限,人们发展的模型仅考虑了近地情况,而对于远地弓激波的位型,以及其他因素例如行星际磁场B_y对弓激波位型的影响,人们还不是很清楚.通过统计分析ARTEMIS卫星2011年1月至2015年1月期间的弓激波穿越事件,首先拟合修正了Chao弓激波模型(最常用的弓激波模型之一)中尾部张角a表达式的系数,得到适用于中远地(月球轨道处,地心距离-20R_EX-50R_E)弓激波的模型系数,然后研究了行星际磁场B_y分量对弓激波尾部张角a的影响.结果表明:(1)拟合的模型系数相对于原系数来说,在中远地与观测结果更吻合;(2)弓激波尾部张角a随行星际磁场B_y分量的增大而增大,且正的B_y对张角的影响比B_y为负的情况影响更大.研究结果为进一步建立包含行星际磁场B_y分量的弓激波模型提供了参考.     

地球磁层对磁云边界层的大尺度响应分析——个例研究

主要分析了WIND飞船2004年11月9日探测的磁云边界层引起的大尺度地球磁层活动.磁层响应主要包括以下3个方面:(1)磁云边界层内本身持续较强南向磁场驱动了一个强磁暴的主相.(2)由于磁云边界层内部较强南向磁场持续一段时间后发生向北偏转触发了一个典型磁层亚暴.文中详细分析了亚暴膨胀相发生时夜侧磁层各区域的观测现象,包括极光观测、高纬地磁湾扰、地球同步轨道无色散粒子注入现象、Pi2脉动突然增强以及等离子体片偶极化现象等.(3)磁云边界层和前面鞘区组成一个动压增强区,此动压增强区强烈压缩磁层,致使磁层顶进入地球同步轨道以内;当磁云边界层扫过磁层时,位于向阳侧地球同步轨道上的两颗GOES卫星大部分时间位于磁层磁鞘中,以致很长时间内直接暴露在太阳风中.利用Shue(1998)模型计算得到当磁云边界层扫过磁层时磁层顶日下点的位置被压缩至距地心最近距离为5.1RE,磁云边界层的强动压结构以及强间断面决定了磁云边界层对磁层的强压缩效应.强动压结构、多个强间断结构以及持续较长时间的强南向磁场是许多磁云边界层的共性,这里以此磁云边界层事件为例分析了磁云边界层的地球磁层响应.     

大尺度场向电流及其与单色极光电子的联系--Swarm卫星观测

Swarm卫星A/C在480km左右高度伴飞,通过二者磁场观测数据,可在不需假设无限大垂直电流片的情况下更加真实地计算出场向电流(FAC).本文利用最新的Swarm观测数据,研究了大尺度场向电流的时空分布特征,及其对行星际条件的依赖;结合极光沉降粒子时空分布信息,探究了场向电流可能载流子及其源区.分析发现:(1)IMF Bz分量主要控制FAC的强度大小,By分量主要改变FAC的结构与分布,最为明显的是0区FAC;(2)昏侧1区上行FAC与单色极光电子的高发区域具有较高的重合度,且在不同行星际条件下均表现出相类似的纬度分布;(3)在上述区域内,FAC密度与单色极光电子能通量表现出较好的相关性.这表明单色极光电子对昏侧1区上行电流起着重要贡献.     

磁暴期间亚极光区极化流（SAPS）的DMSP观测与RAM模拟的比较研究

亚极光区极化流（Subauroral Polarization Streams, SAPS）为快速流动的西向等离子体流,位于昏侧-子夜前亚极光区,是磁层-电离层-热层耦合的重要过程之一.本文利用密西根大学的RAM （Ring current-Atmosphere Interaction Model）模型对一次典型磁暴期间发生的SAPS事件进行了模拟,并与DMSP卫星观测值进行了比较.结果表明：模拟结果能大致反映观测现象;模拟得到的SAPS峰值速度所在纬度随磁暴时间的变化与观测值有较大差别;SAPS速度观测值在约18∶00 UT和约20∶00 UT左右出现两个峰值,而模拟值只有一个峰值,出现在约18∶00 UT,主要原因是模型对亚暴过程的模拟存在不足.     

地球磁层对磁云边界层的大尺度响应分析——个例研究

主要分析了WIND飞船2004年11月9日探测的磁云边界层引起的大尺度地球磁层活动．磁层响应主要包括以下3个方面：（1）磁云边界层内本身持续较强南向磁场驱动了一个强磁暴的主相．（2）由于磁云边界层内部较强南向磁场持续一段时间后发生向北偏转触发了一个典型磁层亚暴．文中详细分析了亚暴膨胀相发生时夜侧磁层各区域的观测现象,包括极光观测、高纬地磁湾扰、地球同步轨道无色散粒子注入现荆、Pi2脉动突然增强以及等离子体片偶极化现象等．（3）磁云边界层和前面鞘区组成一个动压增强区,此动压增强区强烈压缩磁层,致使磁层顶进入地球同步轨道以内;当磁云边界层扫过磁层时,位于向阳侧地球同步轨道上的两颗GOES卫星大部分时间位于磁层磁鞘中,以致很长时间内直接暴露在太阳风中．利用Shue（1998）模型计算得到当磁云边界层扫过磁层时磁层顶日下点的位置被压缩至距地心最近距离为5．1RE,磁云边界层的强动压结构以及强间断面决定了磁云边界层对磁层的强压缩效应．强动压结构、多个强间断结构以及持续较长时间的强南向磁场是许多磁云边界层的共性,这里以此磁云边界层事件为例分析了磁云边界层的地球磁层响应．     

南向行星际磁场事件与磁暴关系的研究

利用172-182年IMP-8飞船的太阳风观测资料和相应地磁活动性指数Dst和AE,研究了43个南向行星际磁场事件期间太阳风和磁层的耦合问题. 与这43个事件对应的地磁暴是中等的和强的磁暴(Dst＜-50nT). 结果表明:(1) 在43个事件中有11个(约占25.6髎)紧随激波之后,18个处于激波下游流场中(占42髎),其余14个(占33髎)和激波没有关连. 绝大多数事件都伴有太阳风动压和总磁场强度的增加;(2) 当行星际晨昏向电场强度EI＞-4mV/m时,只引起磁亚暴,对Dst指数没有明显影响. 仅当EI＜-5mV/m时,磁亚暴和磁暴才会同时出现;(3) 太阳风动压的增加会增强能量向环电流的输入,但不是密度和速度单独起作用,而是以PK=ρV2的组合形式影响能量的输入;(4) 虽然行星际磁场(IMF)南向分量BZ对太阳风和磁层的耦合起着关键作用,但IMF的BX和BY分量相对于BZ的大小对太阳风向磁层的能量传输也有一定影响. 当BX、BY相对BZ较大时能量耦合加强.     

基于范阿伦双星EMFISIS观测数据的NWC和NAA人工甚低频台站信号的内磁层全球统计分布

地球表面的人工甚低频台站信号可以穿透电离层泄漏进地球磁层导致内辐射带电子沉降到两极大气.因此研究人工甚低频台站信号的空间全球分布特性对于分析辐射带电子的损失具有重要科学意义.本文使用范阿伦双星从2013年到2018年共计6年的高质量的波动观测数据,统计了 NWC(19.8 kHz)、NAA(24.0 kHz)两个人工VLF台站信号的全球分布,分析了台站信号的电场功率谱密度对地理经纬度、磁壳值L、磁地方时MLT、地磁活动水平的依赖性.结果表明,在内磁层中,人工台站VLF信号主要沿着台站位置对应的磁力线传播,夜侧强度高于日侧,冬季高于夏季.这种日夜和夏冬差异的形成是因为夜侧和冬季的日照强度较弱,电离层电子密度较低,VLF信号较容易穿透电离层进入磁层.此外人工VLF台站信号的全球分布受地磁活动的影响很弱.这些统计观测结果给出了 NWC和NAA两个重要人工VLF台站信号强度的全球分布特征,为进一步分析人工VLF台站信号与地球辐射带电子的波粒相互作用提供了关键信息.     

Auroral fading structure before breakup: A review

This review is devoted to auroral fading before beginning of the substorm active phase. This initial stage of the active phase called breakup is accompanied by a sharp brightening of auroras and their rush toward the pole. Auroral fading before breakup was first detected in discrete auroras in the nightside sector and consisted in that a short-term decrease in brightness of an arc moving toward the equator below the level observed during the preliminary phase was observed during the substorm preliminary phase 2–3 min before breakup. During fading, the velocity of equatorward motion of auroral arcs decreased up to their complete stoppage. Auroral fading in the noon sector was registered simultaneously with fading on the Earth’s nightside before the beginning of the active phase. Short-term background fading was also observed both equatorward and poleward of an arc on the nightside. It was subsequently indicated that similar fading is observed in various geophysical phenomena. It was detected that a radar aurora signal fades before breakup, if auroral substorm is observed in a radar pattern and substorm source is located under good aspect conditions. Riometer absorption decreases simultaneously with auroral fading. Geomagnetic pulsations decay on dayside and nightside immediately before breakup. Such a multiform manifestation of fading in various geophysical phenomena indicates that fading is related to some global processes proceeding in the magnetosphere when energy accumulation in this region comes to the end before its explosive release into the polar ionosphere.     

亚暴期间极光电集流带的变化

极光活动加剧和极光电集流增强是磁层-电离层能量耦合的两种重要表现形式,它们同为磁层带电粒子向电离层沉降的结果,但是变化规律却非常不同.本文用地基磁场资料,反演极区等效电流体系,研究地磁平静期和扰动期极光电集流带的运动特点.研究表明,Harang间断把极光电集流带分为两段：下午—黄昏段的东向电集流带较弱,而晨侧和子夜—凌晨段的西向电集流带较强.在亚暴膨胀相,随着AE指数增大,整个极光卵向赤道扩展,而极光电集流带却表现出分段差异的特点：下午—黄昏东向电集流带向低纬移动,晨侧西向电集流带也向赤道移动,而子夜—凌晨西向电集流带则向极移动.电动力学分析表明,在不同地方时段,控制电流的主要因素不同,因而,电流及其磁扰有不同的特点：下午—黄昏东向电集流和晨侧西向电集流组成了DP2电流体系,主要受控于磁层对流电场,反映了“驱动过程”的行为;而子夜—凌晨西向电集流是DP1电流体系的基本部分,主要受控于电导率,反映了“卸载过程”的特点.     

Interplanetary Shocks, Magnetopause Boundary Layers and Dayside Auroras: The Importance of a Very Small Magnetospheric Region

Dayside near-polar auroral brightenings occur when interplanetary shocks impinge upon the Earth's magnetosphere. The aurora first brightens near local noon and then propagates toward dawn and dusk along the auroral oval. The propagation speed of this wave of auroral light is 10 km s^-1 in the ionosphere. This speed is comparable to the solar wind speed along the outer magnetosphere. The fundamental shock-magnetospheric interaction occurs at the magnetopause and its boundary layer. Several physical mechanisms transferring energy from the solar wind directly to the magnetosphere and from the magnetosphere to the ionosphere are reviewed. The same physical processes can occur at other solar system magnetospheres. We use the Haerendel (1994) formulation to estimate the acceleration of energetic electrons to 50 keV in the Jovian magnetosphere/ionosphere. Auroral brightenings by shocks could be used as technique to discover planets in other stellar systems.     

The discovery and the first studies of the auroral oval: A review

The auroral oval concept radically changed the view that existed for a century in geophysics on the patterns in aurora planetary spatial–temporal distributions. The auroral zone, which is located around the geomagnetic pole as a continuous ring at a constant angular distance of ~23°, was replaced by the auroral oval in 1960. The auroral oval spatial position reflects the shape of the Earth’s magnetosphere, which is compressed by the solar wind on the dayside and stretches into the magnetotail on the nightside. The oval is fixed relative to the direction toward the Sun and is located around the geomagnetic pole at altitudes of the upper atmosphere at an angular distance of ~12° at noon and ~23° at midnight. After an animated discussion over several subsequent years, the existence of the auroral oval was accepted by the scientific community as a paradigm of a new science, i.e., solar–terrestrial physics. The oval location indicates the zone where electron fluxes with energies varying from ~100 eV to ~20 keV precipitate into the upper atmosphere and is related to the structure of plasma domains in the Earth’s magnetosphere. The paper describes the scientific studies that resulted in the concept of the auroral oval existence. It has been shown how this concept was subsequently justified in the publications by Y.I. Feldstein and O.B. Khorosheva. The issue of the priority of the auroral oval concept introduction into geophysics has been considered. The statement that the concept of the oval is an archaic paradigm of solar–terrestrial physics has been called into question. Some scientific fields in which the term auroral oval or simply oval was and is the paradigm have been listed.     

The dynamic cusp aurora on 30 November 1997: response to southward turning of the IMF

We document the detailed dynamics of the dayside aurora in the ≈1200–1600 MLT sector in response to a sharp southward turning of the interplanetary magnetic field (IMF) under negative IMF B_y conditions. Features not documented in previous work are elucidated by using two meridan scanning photometers (separated by 2 h) and an all-sky auroral imager in Ny Ålesund, Svalbard (75.5^MLAT) in combination with magnetograms from stations on Svalbard, covering the latitude range 71^–75^MLAT. The initial auroral response may be divided into three phases consisting of: (1) intensification of both the red (630.0 nm) and green (557.7 nm) line emissions in the cusp aurora near 1200 MLT and ≈100 km equatorward shift of its equatorward boundary, at ≈75^MLAT, (2) eastward and poleward expansions of the cusp aurora, reaching the 1430 MLT meridian after 5–6 min, and (3) east-west expansion of the higher-latitude aurora (at ≈77^–78^MLAT) in the postnoon sector. The associated magnetic disturbance is characterized by an initial positive deflection of the X-component at stations located 100–400 km south of the aurora, corresponding to enhanced Sunward return flow associated with the merging convection cell in the post-noon sector. The sequence of partly overlapping poleward moving auroral forms (PMAFs) during the first 15 min, accompanied by corresponding pulsations in the convection current, was followed by a strong westward contraction of the cusp aurora when the ground magnetograms indicated a temporary return to the pre-onset level. These observations are discussed in relation to the Cowley-Lockwood model of ionospheric response to pulsed magnetopause reconnection.     

X射线极光强度与亚暴指数AE的相关关系

研究了Polar卫星的极区电离层X射线成像仪（PIXIE）得到的极光X射线成像强度AI（Auroral Intensity）与磁层亚暴指数的相关关系.本文发现,在所选取的1997年至2001年的部分数据中,从完整的X射线图像得到的极光X射线总强度和AE指数有很好的线性相关关系,在全部83组数据中有566％的数据的线性相关系数都在060以上（相关系数最大为097）.所以本文认为极光X射线总强度可以作为新的磁层亚暴卫星实时监测指数.     

亚暴期间高纬黄昏-子夜扇区极光弧增亮与衰减及其与IMF的关系

利用南极中山站极光全天空摄相、地磁、地磁脉动数据和Wind卫星的行星际磁场IMF观测数据，分析了7个亚暴期间高纬黄昏-子夜扇区极光弧的短暂增亮现象.极光弧特征是，短暂增亮随后很快衰减，历时10-20min，基本沿着日-地方向，有明显黄昏方向运动.这些事件大都发生在IMFB_z南转之后，亚暴增长相或膨胀相期间，极光浪涌到达之前10-73min消失.相应的IMFB_x＞0，IMFB_y＜0.这种极光弧和亚暴极光不同，它们与地磁活动及Pi2脉动不相关.这7个极光弧的形态和IMF特征表明，极光弧的增亮很可能由尾瓣重联产生，很快衰减归因于IMFB_z南向条件，而黄昏方向运动受IMFB_y控制.     

Alfven行波涌浪携带的场向电场──极光粒子加速机制

提出一个剪切Ａｌｆｖｅｎ波加速极光粒子的新模式。频率远小于离子回旋频率的Ａｌｆｖｅｎ波由磁层向电离层传播会演化成孤波，当场向电流超过离子声不稳定性的临界电流时，激发离子声不稳定性，波与粒子的相互作用产生反常阻尼使Ａｌｆｖｅｎ波演化成行波涌浪。它携带一个方向向上的平行电场，加速极光电子形成分立极光。对等离子体密度、电场及其对应的电势进行了数值计算，结果发现满足磁层加速区条件形成Ａｌｆｖｎ行波涌浪，提供足够强的加速粒子的电场。     

Planetary features of aurorae: Results of the IGY (a review)

In the period of the International Geophysical Year (IGY), almost the entire planet was covered for the first time by ground-based geophysical observations. Their analysis led to two fundamental results: the existence of the auroral oval and auroral (magnetospheric) substorm. At the final stage of the IGY, satellite explorations of the near-Earth space began. The auroral luminosity appeared to be related to the plasma structure of the magnetosphere. That opened new possibilities for parameters diagnostics of the Earth’s magnetosphere on the basis of ground-based aurora observations. The concepts of auroral oval and magnetospheric substorm became paradigms of the new science of solar-terrestrial physics.     

Planetary distribution of geomagnetic pulsations during a geomagnetic storm at solar minimum

We investigate the features of the planetary distribution of wave phenomena (geomagnetic pulsations) in the Earth’s magnetic shell (the magnetosphere) during a strong geomagnetic storm on December 14–15, 2006, which is untypical of the minimum phase of solar activity. The storm was caused by the approach of the interplanetary magnetic cloud towards the Earth’s magnetosphere. The study is based on the analysis of 1-min data of global digital geomagnetic observations at a few latitudinal profiles of the global network of ground-based magnetic stations. The analysis is focused on the Pc5 geomagnetic pulsations, whose frequencies fall in the band of 1.5–7 mHz (T ～ 2–10 min), on the fluctuations in the interplanetary magnetic field (IMF) and in the solar wind density in this frequency band. It is shown that during the initial phase of the storm with positive IMF Bz, most intense geomagnetic pulsations were recorded in the dayside polar regions. It was supposed that these pulsations could probably be caused by the injection of the fluctuating streams of solar wind into the Earth’s ionosphere in the dayside polar cusp region. The fluctuations arising in the ionospheric electric currents due to this process are recorded as the geomagnetic pulsations by the ground-based magnetometers. Under negative IMF Bz, substorms develop in the nightside magnetosphere, and the enhancement of geomagnetic pulsations was observed in this latitudinal region on the Earth’s surface. The generation of these pulsations is probably caused by the fluctuations in the field-aligned magnetospheric electric currents flowing along the geomagnetic field lines from the substorm source region. These geomagnetic pulsations are not related to the fluctuations in the interplanetary medium. During the main phase of the magnetic storm, when fluctuations in the interplanetary medium are almost absent, the most intense geomagnetic pulsations were observed in the dawn sector in the region corresponding to the closed magnetosphere. The generation of these pulsations is likely to be associated with the resonance of the geomagnetic field lines. Thus, it is shown that the Pc5 pulsations observed on the ground during the magnetic storm have a different origin and a different planetary distribution.