磁层系统的能量输入、输出与日地耦合

用１９７８年和１９８２年３６个磁暴期间的太阳风、行星际磁场（ＩＭＦ）和地磁资料，分析和检验已有的两类太阳风－磁层能量耦合函数．结果表明：Ａｋａｓｏｆｕ提出的耦合函数ε能大致地预报亚暴和磁暴的发生。ε开始起重要作用时即出现亚暴；电离层能耗达到饱和值是发生磁暴的标志。ε与磁层体系能耗之间有接近于对数量的线性关系．用１９７８－１９８６年的资料，分析环电流和极光区电离层能耗在１２１个太阳自转周内的分布表明，日面上可能存在相对持久的活动区域     

行星际磁场北向时太阳风－磁层的能量耦合

利用量纲分析法研究太阳风磁层的能量耦合问题。得到了在考虑磁层对太阳风的粘滞作用情况下，行星际磁场北向时的太阳风－磁层能量耦合函数，并首次在耦合函数中引入太阳风温度变量，在此基础上得到了一般情况下的太阳风－磁层耦合函数．     

行星际磁场北向时太阳风－磁层的能量耦合

利用量纲分析法研究太阳风磁层的能量耦合问题。得到了在考虑磁层对太阳风的粘滞作用情况下，行星际磁场北向时的太阳风－磁层能量耦合函数，并首次在耦合函数中引入太阳风温度变量，在此基础上得到了一般情况下的太阳风－磁层耦合函数．     

磁暴期间太阳风-磁层-电离层间的耦合过程

本文用行星际和地面磁场以及电离层资料,讨论了三次磁暴期间高、中纬电离层电场对太阳风和磁层内变化的响应。 分析表明,当IMF的B_x分量由北向转为南向时,太阳风驱动的磁层对流变化能直接反映出高纬电离层电位的变化。但持续南向的B_x再次增强时,太阳风输入的主要能量耗损于内磁层过程;电离层的响应表现为一个弛豫过程。当B_x由南转北时,环电流的消失对电离层的作用同样有弛豫的特点。此时,驱动电位已撤消,环电流是维持电离层电位的唯一外源。 本文用电路类比及简单模式法结论对上述几种实测情况进行了讨论。     

对流电场、场向电流和极光区电集流变化的地磁响应

对流电场、场向电流和极光区电集流是磁层一电离层耦合的主要物理过程．它们的演化发展时间分别为几分钟至半小时的量级．本文用１００°Ｅ和３００°Ｅ的两个地磁经度链附近各１１个台站的１ｍｉｎ均值地磁Ｈ和Ｚ分量资料,分析了１９９４年４月１６-１７日磁暴期间磁层耦合过程对极光区和中低纬区电离层扰动的地磁特征．强磁暴开始时,台站所处的地方时位置不同,则观测到的电离层和地磁响应也完全不同．这是磁层对流和一、二区场向电流共同作用的结果．一般说,扰时极光区的西向电集流变化更为强烈．随着耦合的发展,极光区范围会向南北扩展,电集流中心带则向低纬侧移动．在中低纬区,二区场向电流的建立能屏蔽一区场向电流所产生的扰动,并引起反向的电流及地磁变化．由此,中低纬区夜间有可能出现短时间的东向电场,又可通过ＥＸＢ的垂直向上漂移作用抬升Ｆ层等离子体,并发生同一经度链附近的多站电离层ｈ＇Ｆ同时突增现象．另一方面,磁赤道附近的台站则更多地受内磁层赤道环电流和电离层赤道电集流的影响．     

东亚赤道异常区电离层CT诊断──实验及初步结果

国际上第一个低纬电离层层析（ＣＴ）探测台链于１９９３年１１月建成，并开始数据采集．该ＣＴ台链沿１２０°Ｅ子午圈由６个卫星信标差分多普勒接收站组成，北起我国上海，南至菲律宾的马尼拉，纬度覆盖范围约２０°．该台链专为电高层赤道异常区电子密度大尺度结构ＣＴ成像而设计，其目的是监测研究赤道异常形态与动力学、电离层等离子体泡、行优以及暴时磁层－电离层－热层耦合过程等重要的赤道与低纬区电离层现象．本文介绍该低纬电离层ＣＴ实验的有关技术问题，包括接收台站布设、实验设备、数据采集软件和数据预处理方法．文中还给出利用ＣＴ技术，由实测斜电子含量数据反演电离层电子密度二维分布图像的几个实例．结果表明，利用低纬电离层ＣＴ台链可以有效地监测电离层赤道异常及其它低纬电高层电子密度大尺度结构的时空变化．     

中国高层大气与电离层耦合研究进展

近年来,地球高层大气与电离层之间的耦合研究为众多学者所关注.在回顾这一领域国际上若干研究方向进展的基础上,着重介绍了中国学者的近期研究工作与贡献.首先,扼要介绍了中国高层大气观测的新发展,包括激光雷达、FP干涉仪、全天空气辉成像仪等光学探测,MST雷达、全天空流星雷达等无线电探测手段.在高层大气变化特性研究中,介绍了高层大气的气候学及各种大气波动的研究进展.在高层大气与低电离层的耦合研究方面,介绍了突发钠层及低热层钠层的观测研究和钠层模式的研究进展,以及突发E层与大气行星波之间的耦合研究工作.在高层大气波动过程与电离层F2层耦合研究中,着重介绍了电离层四波经度结构与高层大气非迁移潮汐之间的耦合特性与机理研究.在热层与电离层耦合的研究方向上,介绍了热层背景大气风场和重力波对电离层的作用、带电粒子对赤道热层的影响与热层赤道异常的形成机理研究等热层电离层相互耦合工作.综合认为,近年来中国学者在高层大气与电离层耦合的研究领域进行了大量工作,包括实验观测及数据分析、模式化与理论研究等.中国学者取得的研究成果为这一领域近年来的进展与突破做出了重要贡献.     

用非相干散射雷达链的观测资料研究高、低纬电离层间的耦合

本文用美国NCAR非相干散射雷达链的观测资料进行了两个事例分析。结果表明,在所选事例的中、弱磁扰期间,高低纬电离层间以动力耦合效应为主,即扰动电离层发电机的特征较明显。由于赤道电离层特性和赤道站雷达观测灵敏度较高,从而也观测到与扰动电场从高纬直接穿透过来相关的电动耦合现象。最后,对有关的物理过程进行了讨论。     

基于行星际/太阳风和地磁条件的紫外极光卵边界建模和预测

极光卵的尺度大小与太阳风-磁层-电离层能量耦合过程紧密相关,准确预测其大小对空间天气研究和预报具有非常重要的意义.本文基于模糊c均值聚类算法,从Polar卫星紫外极光图像中自动提取极光卵边界数据(~1215000个赤道向边界点和~3805000极向边界点),统计分析其与太阳风等离子体、行星际磁场、地磁指数等之间的相关特性,并构建了以行星际、太阳风为模型参数(模型1)和以行星际、太阳风及地磁指数为模型参数(模型2)的2种极光卵边界多元回归模型.以模型预测的极光卵边界与实际极光卵边界之间的平均绝对误差作为模型评价标准,将本文预测模型与Carbary(2005)模型和Milan(2009)模型进行了对比.结果表明,模型2对极光卵极向、赤道向边界预测的平均绝对误差为1.55和1.66地磁纬度,优于Carbary和Milan模型(Carbary模型极向、赤道向边界的平均绝对误差为2.18和5.47地磁纬度,Milan模型极向、赤道向边界的平均绝对误差为1.71地磁纬度和1.90地磁纬度).     

大气重力波产生的大尺度赤道电离层扰动

本文研究了大气重力波产生的大尺度赤道电离层扰动的性质．当重力波的传播方向与磁场方向倾斜相交时，重力波在Ｆ区产生行进电离层扰动．当重力波垂直于磁场传播时，能触发等离子体Ｒａｙｌｅｉｇｈ－Ｔａｙｌｏｒ不稳定性，形成大尺度赤道扩展Ｆ不均匀体．重力波引起的扩展Ｆ主要出现于晚上，行进电离层扰动则可能出现于任何时间．本文建立了行进电离层扰动和大尺度赤道扩展Ｆ的统一理论模型，深入全面地揭示了电离层扰动的性质．     

Solar wind-magnetosphere-ionosphere coupling and chaotic dynamics

Electromagnetic fields and currents connect various regions of the earth's near space environment extending upto the magnetopause. Realization of this fact has lead to the concept of Global Electric Circuit (GEC) to describe the electromagnetic environment of the earth's atmosphere. Solar wind - magnetosphere - ionosphere coupling forms a vital component of GEC. Magnetospheric substorms represent a global interaction between the solar wind, the magetosphere, and the ionosphere. This article gives an overview of the solar wind - magnetosphere- ionosphere coupling processes with emphasis on the nonlinear particle dynamics in the magnetotail. Those aspects of the substorm processes which involve the chaotic dynamics are highlighted. Various methods based on nonlinear particle dynamics, linear prediction filtering techniques, phase space reconstruction techniques, and dynamical anologue models of geomagnetic activity are reviewed. It is shown that the solar wind- magnetosphere - ionosphere system behaves as a strongly coupled nonlinear dynamical system which could be driven from regular to chaotic behavior with low dimensionality when the solar wind forcing is strong enough.     

Midday reversal of equatorial ionospheric electric field

A comparative study of the geomagnetic and ionospheric data at equatorial and low-latitude stations in India over the 20 year period 1956–1975 is described. The reversal of the electric field in the ionosphere over the magnetic equator during the midday hours indicated by the disappearance of the equatorial sporadic E region echoes on the ionograms is a rare phenomenon occurring on about 1% of time. Most of these events are associated with geomagnetically active periods. By comparing the simultaneous geomagnetic H field at Kodaikanal and at Alibag during the geomagnetic storms it is shown that ring current decreases are observed at both stations. However, an additional westward electric field is superimposed in the ionosphere during the main phase of the storm which can be strong enough to temporarily reverse the normally eastward electric field in the dayside ionosphere. It is suggested that these electric fields associated with the V × Bz electric fields originate at the magnetopause due to the interaction of the solar wind and the interplanetary magnetic field.     

Specification and forecasting of scintillations in communication/navigation links: current status and future plans

The ionosphere often becomes turbulent and develops electron density irregularities. These irregularities scatter radio waves to cause amplitude and phase scintillation and affect satellite communication and GPS navigation systems. The effects are most intense in the equatorial region, moderate at high latitudes and minimum at middle latitudes. The thermosphere and the ionosphere seem to internally control the generation of irregularities in the equatorial region and its forcing by solar transients is an additional modulating factor. On the other hand, the irregularity generation mechanisms in the high-latitude ionosphere seem to be driven by magnetospheric processes and, therefore, high-latitude scintillations can be tracked by following the trail of energy from the sun in the form of solar flares and coronal mass ejections. The development of a global specification and forecast system for scintillation is needed in view of our increased reliance on space-based communication and navigation systems, which are vulnerable to ionospheric scintillation. Such scintillation specification systems are being developed for the equatorial region. An equatorial satellite equipped with an appropriate suite of sensors, capable of detecting ionospheric irregularities and tracking the drivers that control the formation of ionospheric irregularities, has also been planned for the purpose of specifying and forecasting equatorial scintillations. In the polar region, scintillation specification and forecast systems are yet to emerge although modeling and observations of polar cap plasma structures, their convection and associated irregularities have advanced greatly in recent years. Global scintillation observations made during the S-RAMP Space Weather Month in September 1999 are currently being analyzed to study the effects of magnetic storms on communication and navigation systems.     

Sun–Earth geometry,geomagnetic activity,and planetary F2 layer ion density: Part I: Signatures of magnetic reconnection

Our previous quantitative analyses have shown that geomagnetic activity and planetary ion density of the F2 layer of the ionosphere seem to share the same parent cause, the solar wind, whose entry into geospace is controlled by the Sun–Earth geometry. The thrust of this paper is four fold: (a) to establish the reality of this not clearly recognized connection, (b) to demonstrate that geomagnetic activity varies seasonally with three separate and independent components, viz. a semiannual, an annual and a Sun–Earth-distance determined component, all of which can be accurately derived from solar–terrestrial geometry alone, (c) to evaluate the contribution of each of these components which, taken together, appear to represent the steady-state signatures of the mechanism of magnetopause reconnection, and (d) to highlight the fact that the currently used planetary geomagnetic indices are deficient and therefore need to be revised. Since detailed understanding of the precise mechanism of the entry of solar wind energy into geospace is still lacking, no mechanism is suggested to show how solar wind energy is transported to the F2 layer (including low and equatorial latitudes). Magnetospheric electric fields, precipitation of energetic neutrals produced through charge exchange reactions with ions in the ring current and radiation belt particles, Joule heating, etc., may all be involved, but the energy for all such processes still comes from the solar wind. Apart from the three components of the reconnection mechanism mentioned above, a steady component due to the viscous interaction mechanism should also be present.     

Morphological aspects of a new type of counter electrojet event

The study describes the time and space morphologies of a rather new type of counter electrojet event on the basis of data from the excellent chain of magnetic and ionospheric observatories along the Indo-Russian longitude sector. Abnormally large westward currents are observed during almost the whole of the daytime hours on a series of days. These events do not form any vortices in the current system and do not apparently seem to be associated with tidal effects or any solar magnetosphere events or geomagnetic disturbances. The existence of a westward electric field over the equatorial ionosphere has been confirmed by the absence of an equatorial type of sporadic E in the ionograms at Thumba precisely during the periods when H at Trivandrum minus H at Alibag is negative. The equatorial F region anomaly was also absent on the counter electrojet day. Such counter electrojet events during the northern winter months of low solar activity years are suggested to be the result of the modified wind system in the ionosphere associated with stratospheric warming events.     

中纬电离层的低频等离子体不稳定性

本文研究了中纬电离层Rayleigh-Taylor不稳定性和漂移不稳定性的基本性质.如果不存在中性风和背景电场,中纬Rayleigh-Taylor不稳定性的增长率比赤道相应条件下的小.中性风和电场对中纬Rayleigh-Taylor不稳定性有重要影响.当中性风速度达到10m/s时,其作用就超过了重力.漂移不稳定性也受到重力、中性风和电场的影响,离子-中性粒子碰撞能降低漂移不稳定性的增长率.本文的分析表明,在赤道电离层容易产生大尺度的Rayleigh-Taylor不稳定性,在中纬电离层易产生小尺度的漂移不稳定性.