多频段EMIC波共振散射辐射带相对论电子的损失时间尺度研究

作为地球磁层中一种分布广泛的电磁波，电磁离子回旋波(Electromagnetic ion cyclotron waves,简称EMIC波)是地球辐射带相对论电子的重要损失机制.EMIC波通常呈现H⁺、He⁺和O⁺三种不同频段，不同频段对相对论电子的散射效应和损失时间尺度大不相同.准线性理论是定量分析不同频段EMIC波对地球辐射带相对论电子散射效应的重要工具，我们利用基于准线性理论开发的Full Diffusion Code(FDC),分别计算了H⁺、He⁺、O⁺三种频段EMIC波在不同空间范围、背景等离子体条件以及不同传播角模型下对辐射带相对论电子的弹跳平均投掷角散射系数，建立了L=1.5～7,背景等离子体参数α^*(=f_pe/f_ce)=6～30范围内的多频段EMIC波电子散射系数矩阵库.进而，我们计算了辐射带相对论电子在不同频段EMIC波散射作用下的损失时间尺度，获得了在不同磁层条件下EM...     

2003年Hallowe’en磁暴后新质子带形成和损失机制的研究

本文利用低高度极轨卫星NOAA/POES的观测数据,对2003年Hallowe'en磁暴期间新质子带的形成和损失机制做了细致的研究和分析.结果表明新质子带的形成是诸多因素共同作用的结果.包括强太阳质子事件(Solar Proton Events,SPEs)、大的地磁暴和行星际激波.所有这些因素构成了新质子带形成的前提条件,尤其是行星际激波是形成新质子带不可缺少的因素.此外本文提出了磁暴主相对高能质子注入磁层稳定捕获区起到重要贡献.本文还运用绝热捕获判据分析了新质子带的损失机制,证明了由于磁暴期间环电流积累造成磁场大的扰动,破坏绝热不变量的守恒,导致新质子带粒子的损失.     

2003年Hallowe′en磁暴后新质子带形成和损失机制的研究

本文利用低高度极轨卫星NOAA/POES的观测数据,对2003年Hallowe'en磁暴期间新质子带的形成和损失机制做了细致的研究和分析. 结果表明新质子带的形成是诸多因素共同作用的结果,包括强太阳质子事件（Solar Proton Events, SPEs）、大的地磁暴和行星际激波.所有这些因素构成了新质子带形成的前提条件,尤其是行星际激波是形成新质子带不可缺少的因素.此外本文提出了磁暴主相对高能质子注入磁层稳定捕获区起到重要贡献.本文还运用绝热捕获判据分析了新质子带的损失机制,证明了由于磁暴期间环电流积累造成磁场大的扰动, 破坏绝热不变量的守恒,导致新质子带粒子的损失.     

基于CARISMA地磁台链观测的IPDP事件的统计分析

亚暴期间磁尾等离子体片离子注入内磁层能够激发电磁离子回旋(EMIC)波.对应于这种EMIC波,地面磁力仪可观测到周期逐渐减小的地磁脉动(IPDP).利用GOES卫星数据,地磁指数和加拿大CARISMA地磁台站的数据,我们研究了IPDP事件的产生与亚暴磁尾注入的关系.同时利用CARISMA地磁台链中的MCMU和MSTK两个台站,从2005年4月到2014年5月期间的观测数据,统计分析了亚暴期间的IPDP事件,研究了IPDP事件的出现率关于季节和磁地方时的分布特征.我们总共获得128个两个台站同时观测的IPDP事件.该类事件关于季节分布的发生率,冬季最小,为13.28%,春季最大,为32.81%,结果表明IPDP事件关于季节分布的发生率受到电离层电导率及亚暴发生率的影响.两个台站同时观测到的IPDP事件最大出现率出现在15—18 MLT(磁地方时),结果表明IPDP事件主要由亚暴期间产生的能量离子注入内磁层,西向漂移遇到等离子体层羽状结构(Plume)区的高密度等离子体所激发.     

地磁亚暴期间低高度ENA辐射事件的抵近观测与反演

2004年11月12日的系列地磁亚暴期间, TC-2卫星上的中性原子成像仪(NUADU)在飞临近地点附近的南、北极上空观测到低高度能量中性原子(ENA)辐射.通过对高时空分辨探测数据的反演,我们首次给出亚暴期间环电流能量离子沉降和注入过程的全球视场展示,展示的时间分辨率高达1min.探测结果表明,观测到的ENA辐射主要来自低高度、高纬极区.由于沉降能量离子沿磁力线运动,在该区域通过电荷交换产生ENA的几率更大.因此,利用低轨道卫星探测高时间和高空间分辨率的ENA成像数据是监测地磁活动期间环电流离子动力学过程演化的最佳方法.     

太阳平静期地磁场与电离层时空变化相互作用分析

作为地球空间环境的重要组成部分,地磁场和电离层是地球物理研究中的重要方向.新的观测数据和处理方法为人们更加深入地认识地磁场和电离层时空变化之间的相互作用发挥了巨大的促进作用.本文利用欧洲轨道测定中心(CODE)提供的全球电离层垂直总离子浓度地图(GIM)数据和Swarm卫星的观测数据,基于数据统计的方法,对太阳平静期不同纬度地区地磁场和电离层时空变化之间的相互作用进行了分析.从地磁场对电离层时空变化的作用来看,本文利用Swarm卫星数据发现电离层电子浓度在赤道地区呈"马鞍"形分布,在高纬度地区变化剧烈,验证了因地磁场对电离层时空变化影响导致的电离层赤道异常和极盖吸收等现象的存在,同时利用GIM数据通过张量秩-2分解和主成分析发现沿地磁场方向电离层的空间变化更加迅速,体现出地磁场对电离层时空变化的约束作用.从电离层对地磁场时空变化的作用来看,基于CHAOS-5模型对地磁内源场和磁层环电流磁场的预测,本文从Swarm卫星磁测数据中分离出电离层中电流体系的磁效应,其中包括赤道电集流、中纬度地区的Sq电流体系和极区电集流的磁效应,为进一步反演电离层电流体系奠定了基础.     

NOAA系列卫星高能粒子数据一致性统计分析

顶部电离层是低轨道卫星的运行空间,是能量粒子沉降的重要区域,认识这个空间的能量粒子分布特征对研究各种空间天气事件、地震、火山以及其他人类活动引起的扰动具有重要的现实意义.本文利用位于顶部电离层的5颗NOAA系列卫星数据,统计研究了100~300keV的电子和80~2500keV的质子的全球分布特征.研究发现:高能电子和质子主要分布在两极辐射带和南大西洋异常区,两极辐射带观测到的高能电子通量比南大西洋异常区高几倍到一个数量级,而质子则相反;高能电子在两极辐射带地区通量分布具有不对称性,主要表现为在北辐射带西经75°到东经90°存在低值区,相对应的是粒子主要聚集在其磁共轭区,且其边界和南大西洋异常区相交;高能质子两极辐射带对称分布,在南半球东经0°至东经50°存在高值区.利用概率密度统计分析发现,各颗卫星在南大西洋异常区和两极辐射带的高能电子和高能质子通量总体上均呈正态分布.在南大西洋异常区,NOAA-15观测到的高能电子通量比其他卫星的低,NOAA-16观测的高能电子通量比其他卫星的高,各卫星的高能质子观测结果基本相同.在两极辐射带,各卫星观测的高能电子通量结果基本相同,NOAA-18和NOAA-19观测的质子通量最高,NOAA-16和NOAA-17次之,NOAA-15最低,其中NOAA-19比NOAA-15观测到的质子通量要高一个数量级左右.在磁暴期间顶部电离层高能电子的变化表明地磁指数Dst和空间粒子通量变化具有时间同步性.本文的研究成果将为我国下一代电磁卫星设计提供基础依据.     

南极中山站F-lacuna特征分析

F-lacuna是高纬极区电离层测高仪频高图上经常出现的一种F层回波描迹部分或全部消失的现象,直接影响电离层参数的标定,其表征的电离层物理过程尚未定论.利用南极中山站测高仪频高图数据,本文统计分析了Flacuna在不同太阳风速度水平下的发生频率,主要对2012年2月15日一次F2-lacuna观测实例的粒子沉降及电离层特性进行了分析.观测特征表明,F2-lacuna发生期间,电离层电子总含量TEC明显减小,昭和站SuperDARN高频雷达观测到的中山站上空电离层Bragg后向散射增强,但对应来自磁层的电子和离子沉降并不明显.这可能是由磁层亚暴引起的极区电离层电流体系扰动,触发电离层F-B不稳定性,产生沿场向排列的小尺度不规则体,其热效应导致F2层密度减小,F2-lacuna出现.     

电离层人工调制激发的VLF波在磁层的传播特性及应用研究

电离层人工调制可以激发甚低频（VLF）波,其中向上传播进入磁层的VLF波,不但能够用来研究磁层中的各种物理现象,且具有人工沉降高能粒子,消除辐射带等实际用途.本文使用射线追踪方法,模拟电离层调制激发的VLF波在磁层的传播路径,分析激发纬度和调制频率对传播路径和传播特性的影响;并基于低频波的色散方程和波粒共振条件,分析VLF波传播路径上与磁层高能粒子的最低共振能及其分布.研究表明,VLF波通过在磁层来回反射向更高的L-shell传播,最终稳定在某一L-shell附近.以较低的调制频率或者从较高的纬度激发的VLF波能够传播到更高的L-shell,但是,当激发纬度过高时,低频波也可能不发生磁层反射而直接进入电离层和大气层.低频波在磁层的传播过程中,在较高的纬度或者较低的L-shell能够与较高能量的电子发生共振相互作用,在较高的L-shell并且低纬地区,能够与较低能量的电子发生共振相互作用.共振谐数越高,能发生波粒共振的电子能量越高.     

FY2D卫星与GOES卫星空间粒子观测结果的对比分析

风云二号D星(FY2D)搭载的空间粒子探测器可以观测10～300 MeV的质子和≥350 keV与≥2 MeV的电子.卫星在轨测试阶段,空间粒子探测器观测到了空间环境宁静期间地球同步轨道的电子昼夜周期变化的典型特征,并在卫星发射后的12月15日首次观测到了有代表性的 2级太阳质子事件(SEP),观测到的较高能量质子比较低能量质子更快地恢复到平静时的状态.通过比较FY2D卫星与GOES卫星的探测结果,既显示了同步轨道区域不同位置高能电子通量扰动时间的一致性,也显示了高能电子通量具强烈的晨昏不对称性.通过对太阳质子事件和地磁平静时期该轨道空间高能粒子环境特征的分析和研究,并与GOES卫星同期的观测结果进行相关性分析,结果表明仪器确实具备了监测空间环境扰动和预警能力,探测结果可以用于研究地球同步轨道粒子空间分布、起源和传输等科学目的.     

Relativistic electron losses related to EMIC waves during CIR and CME storms

The losses of radiation belt electrons to the atmosphere due to wave–particle interactions with electromagnetic ion-cyclotron (EMIC) waves during corotating interaction region (CIR) storms compared to coronal mass ejections (CME) storms is investigated. Geomagnetic storms with extended ‘recovery’ phases due to large-amplitude Alfvén waves in the solar wind are associated with relativistic electron flux enhancements in the outer radiation belt. The corotating solar wind streams following a CIR in the solar wind contain large-amplitude Alfvén waves, but also some CME storms with high-speed solar wind can have large-amplitude Alfvén waves and extended ‘recovery’ phases. During both CIR and CME storms the ring current protons are enhanced. In the anisotropic proton zone the protons are unstable for EMIC wave growth. Atmospheric losses of relativistic electrons due to weak to moderate pitch angle scattering by EMIC waves is observed inside the whole anisotropic proton zone. During storms with extended ‘recovery’ phases we observe higher atmospheric loss of relativistic electrons than in storms with fast recovery phases. As the EMIC waves exist in storms with both extended and short recovery phases, the increased loss of relativistic electrons reflects the enhanced source of relativistic electrons in the radiation belt during extended recovery phase storms. The region with the most unstable protons and intense EMIC wave generation, seen as a narrow spike in the proton precipitation, is spatially coincident with the largest loss of relativistic electrons. This region can be observed at all MLTs and is closely connected with the spatial shape of the plasmapause as revealed by simultaneous observations by the IMAGE and the NOAA spacecraft. The observations in and near the atmospheric loss cone show that the CIR and CME storms with extended ‘recovery’ phases produce high atmospheric losses of relativistic electrons, as these storms accelerate electrons to relativistic energies. The CME storm with short recovery phase gives low losses of relativistic electrons due to a reduced level of relativistic electrons in the radiation belt.     

Generation of EMIC Waves in the Magnetosphere and Precipitation of Energetic Protons: Comparison of the Data from THEMIS High Earth Orbiting Satellites and POES Low Earth Orbiting Satellites

Regions of the detection of electromagnetic ion-cyclotron (EMIC) waves on the THEMIS satellites near the equatorial plane and the precipitation of energetic protons on POES low Earth orbiting satellites are compared with the magnetospheric magnetic field model. It is confirmed that low Earth orbiting satellites detect the precipitation of energetic protons in the regon associated with observations of EMIC waves in the magnetosphere. This is consistent with the idea that protons are scattered in the loss cone as a result of ioncyclotron interaction. Thus, observations of fluxes of energetic protons in low Earth orbits can be used to monitor ion-cyclotron instability regions in the magnetosphere. Simultaneous observations at high and low Earth orbits contribute to the construction of a spatiotemporal pattern of the interaction region of EMIC waves and energetic protons. In addition, it is shown that proton precipitation associated with EMIC waves can cause errors in determining the latitude of the isotropic boundary (the equatorial boundary of isotropic fluxes of energetic protons), which is an indicator of the configuration of the magnetic field in the magnetosphere.     

Energetic proton precipitation related to ion–cyclotron waves

This brief review summarizes recent findings related to particle precipitation associated with electromagnetic ion–cyclotron (EMIC) waves seen on the ground as geomagnetic Pc1 and IPDP pulsations.Particle precipitation signatures of ion–cyclotron interaction are described as revealed from low-altitude satellite measurements of the energetic proton fluxes as well as from observations of the proton aurora. As a result, localized proton precipitation patterns situated equatorward of the isotropy boundary are disclosed. One of the patterns is a proton precipitation spot in the morning sector, presumably mapped onto plasmapause; another one is an elongated region of the precipitation, presumably mapped onto the plasmaspheric plume.Clear evidence of the pitch-angle scattering associated with the ion–cyclotron wave activity is found near the equatorial plane in the region conjugated with the localized proton precipitation at low altitude.Thus, the revealed precipitation patterns determine the location of the region of intense pitch-angle scattering of energetic protons, and, therefore, their observations can be used to monitor the region of the ion–cyclotron interaction and to study its origin and properties. Some examples of such application of the low-altitude observations of energetic particles are described.     

On the role of collective interactions in asymmetric ring current formation

The contribution of resonant wave-particle interactions to the formation and decay of the magnetospheric ring current is analysed in the framework of a self-consistent set of equations which take into account azimuthal plasmasphere asymmetry. It is shown that the cyclotron interaction of westward drifting energetic protons with Alfven waves in the evening-side plasmaspheric bulge region leads to the formation of a ring current asymmetry located near 18:00 MLT. The time-scale of this asymmetry is determined by the proton drift time through the plasmaspheric bulge and is about 1 - 3 h. A symmetrical ring current decays mainly due to charge exchange processes. The theory is compared with known experimental data on ions and waves in the ring current and on low-latitude magnetic disturbances. New low-latitude magnetometer data on the magnetic storm of 24 - 26 July 1986 are also discussed. The model presented explains the observed localization of an asymmetrical ring current loop in the evening sector and the difference in relaxation time-scales of the asymmetry and the D_st index. It also explains measured wave turbulence levels in the evening-side plasmasphere and wave observation statistics.     

伴随等离子体密度下降的磁声波与辐射带电子的波粒相互作用及其散射效应

利用范阿伦卫星的高质量观测数据,我们报道了伴随等离子体密度下降的磁声波现象.通过选取分别发生于2013年7月26日(事件A)和2013年9月19日(事件B)的两个相应事件进行细致分析,我们开展试验粒子模拟计算了磁声波对辐射带电子的散射系数,并求解二维福克-普朗克扩散方程量化了磁声波散射导致的辐射带电子动态变化.结果表明,事件A中的磁声波的散射作用主要发生于投掷角范围为60°～80°、能量范围为20～200keV的辐射带电子,而事件B中的磁声波的散射作用主要发生于投掷角范围为50°～80°、能量范围为20～400keV的辐射带电子;两个事件中的磁声波均能导致辐射带电子的蝴蝶状投掷角分布,但是由于事件B的磁声波幅度更强,形成的电子蝴蝶状分布更明显.     

Amplitude–frequency characteristics of ion–cyclotron and whistler-mode waves from Van Allen Probes data

Using two-hour (from 2300 UT January 25, 2013 to 0100 UT January 26, 2013) measurement data from Van Allen Probes on fluxes of energetic particles, cold plasma density, and magnetic field magnitude, we have calculated the local growth rate of electromagnetic ion–cyclotron and whistler-mode waves for field-aligned propagation. The results of these calculations have been compared with wave spectra observed by the same Van Allen Probe spacecraft. The time intervals when the calculated wave increments are sufficiently large, and the frequency ranges corresponding to the enhancement peak agree with the frequency–time characteristics of observed electromagnetic waves. We have analyzed the influence of variations in the density and ionic composition of cold plasma, fluxes of energetic particles, and their pitch-angle distribution on the wave generation. The ducted propagation of waves plays an important role in their generation during the given event. The chorus VLF emissions observed in this event cannot be explained by kinetic cyclotron instability, and their generation requires much sharper changes (“steps”) for velocity distributions than those measured by energetic particle detectors on Van Allen Probes satellites.     

Global distribution of energetic proton precipitations equatorward of the boundary of isotropic fluxes

Based on data of the NOAA POES satellite, the global distribution of the occurrence rate of precipitations of energetic protons (E > 30 keV) equatorward of the boundary of isotropic fluxes has been constructed for the first time. It has been shown that the occurrence rate of proton precipitations inside the zone of anisotropic fluxes is maximum in daytime hours (1100–1600 MLT) at latitudes L = 6–9 and decreases in evening and morning hours. Comparison of the obtained results about proton precipitations with the spatial distribution of the occurrence rate of electromagnetic ion–cyclotron (EMIC) waves in the equatorial magnetosphere according to results of satellite observations demonstrates a close relationship between them. This corroborates that precipitations of energetic protons equatorward of the boundary of isotropic fluxes are a consequence of the development of the ion–cyclotron instability in the equatorial magnetosphere.     

Proton Auroras Equatorward of the Oval as a Manifestation of the Ion-Cyclotron Instability in the Earth’s Magnetosphere (Brief Review)

Different types of proton auroras observed by the IMAGE satellite equatorward of the proton aurora oval are briefly reviewed. These auroras are caused by the precipitation of energetic protons from the Earth’s magnetosphere during the development of the ion-cyclotron instability. In addition to the previously considered types of proton auroras (spots, evening arcs, and dayside flashes), a new type is described: longlasting proton auroras on the dayside. The scheme of interrelation between different proton auroras equatorward of the oval with the distribution of cold plasmaspheric plasma is given.