行星际激波导致的磁尾等离子片中ULF波动事件

磁层中的超低频（ULF）波动在太阳风和磁层之间的能量输运过程中具有重要作用.ULF波动主要发生在内磁层，且内磁层中ULF波动影响粒子的加速及沉降，而在夜侧磁层尤其是磁尾等离子片中观测到的ULF波动比较少.基于中国自主磁层探测卫星TC-1的观测数据，发现了两例行星际激波导致的磁尾中心等离子片中ULF波动事件，并发现这两例ULF事例都包含很强的环向模驻波分量，与以往THEMIS卫星报道的同类事件观测特征相符.根据ULF波的观测特征，分析了这两例ULF波动的可能触发机制.研究结果有助于深入理解磁层对行星际激波的全球响应.      

Statistical survey on sawtooth events,SMCs and isolated substorms

Solar wind driving can cause a variety of different responses in the magnetosphere. Strong and steady driving during geomagnetic storms may result in sawtooth events. Strong to moderate driving may be followed by either sawtooth events or steady magnetospheric convection (SMC) events. Lower solar wind energy input typically leads to the formation of isolated non-storm substorms. This study uses superposed epoch analysis to reveal the typical properties of these three event groups as well as their similarities and differences. We use IMF and solar wind parameters, as well as ground-based indices (AL, SYM-H, ASY-H, PCN) to examine the level of solar wind driving and its response in the magnetosphere. Our results show that sawtooth events are associated with the strongest ionospheric activity. The subgroups of events during constant solar wind _EY$E_Y$ show that the key difference between the events is the average solar wind speed. Particularly, the high activity during sawtooth events is driven by high solar wind speed, while the lowest average speed during the SMCs may explain the lack of substorm activity during the steady convection periods.     

Contribution of geometry of interaction between interplanetary and terrestrial magnetic fields into global magnetospheric state and geomagnetic activity

The paper presents results of our study of dependence of geomagnetic activity from geoeffective parameters taking into account mutual orientation of the interplanetary magnetic field, electric field of the solar wind and geomagnetic moment. We attract a reconnection model elaborated by us made allowance for changes of geometry of the solar wind–magnetosphere interaction during annual and diurnal motions of the Earth. We take as our data base the interplanetary magnetic field and solar wind velocity measured at 1 a.u. at ecliptic plane for the period of 1963–2005 and K_p, D_st, a_m indices. Taken as a whole a geoeffective parameter suggested by us explains 95% of observed variations of the indices. Changes of the geometric factor determined by mutual orientation of the solar wind electric field and geomagnetic moment explain larger than 75% of observed statistical variations of D_st and a_m indices. Based on our results we suggest a new explanation of semi-annual and UT variation of geomagnetic activity.     

A coordinated study of field-aligned currents and Pc5 ULF waves during ejecta 1997

We show examples of long period Pc5 magnetic field pulsations near field-aligned current (FAC) regions in the high-latitude magnetosphere, observed by INTERBALL-Au, and coordinated with POLAR, GOES-9 and ground-based observations during 11 January and 11 April 1997. Identification of corresponding magnetosphere regions and subregions is provided by electrons and protons in the energy-range of 0.01–100 keV measured onboard the spacecraft. The ULF Pc5 wave occurrence is observed in both upward and downward FACs. A fairly good correlation is demonstrated between these ULF Pc5 waves and the consecutive injection of magnetosheath low energy protons. The constancy of the observed frequency peak at 1.8 mHz during quite unsteady solar wind pressure conditions could be reconciled with the surface wave mode model. The 3.1 mHz peak location area probably resembles field-line fluctuations with an interesting appearance of poloidal mode oscillation. It is suggested that the 1.3 mHz wave and its harmonic 2.6 mHz represent global compressional oscillations.     

使用地磁脉动参数定量预报地球同步轨道相对论电子通量的建模研究

磁层超低频波(ULF波)对种子电子的加速机制是磁层相对论电子产生的一个重要机制, 而地磁脉动参数可以作为此机制的有效指标. 本文采用地磁脉动参数作为输入参数, 借鉴线性预测滤波器技术, 构建一个多参量非线性函数, 进而利用此函数以及卡尔曼滤波技术, 建立一个地球同步轨道相对论电子通量日积分值预报模式, 提供提前一天的预报值. 使用2004年数据对该模式进行训练, 预报结果的预报效率为0.73, 线性相关系数为0.85. 使用2005-2006年的数据对该模式进行测试, 预报值与实测值之间的线性相关系数为0.83, 预报效率为0.69, 相比Persistence模式具有较大提升, 与仿REFM模式的预报效率相当      

Study of waves in the magnetotail region with cluster and DSP

The study of the neutral sheet is of fundamental importance in understanding the dynamics of the Earth’s magnetosphere. From the earliest observation of the magnetotail, it has been found that the neutral sheet frequently appears to be in motion due to changing solar wind conditions and geomagnetic activity. Multiple crossings of the neutral sheet by spacecraft have been attributed to a flapping motion of the neutral sheet in the north–south direction, a wavy profile either along the magnetotail or the dawn–dusk direction. Cluster observations have revealed that the flapping motions of the Earth’s magnetotail are of internal origin and that kink-like waves are emitted from the central part of the tail and propagate toward the tail flanks. This flapping motion is shown here to propagate at an angle of ∼45° with x_GSM. A possible assumption that the flapping could be created by a wake travelling away from a fast flow in the current sheet is rejected. Other waves in the magnetotail are found in the ULF range. One conjunction event between Cluster and DoubleStar TC1 is presented where all spacecraft show ULF wave activity at a period of approximately 5 min during fast Earthward flow. These waves are shown to be Kelvin–Helmholtz waves on the boundaries of the flow channel. Calculations show that the conversion of flow energy into magnetic energy through the Kelvin–Helmholtz instability can contribute to a significant part of flow breaking between Cluster and DoubleStar TC1.     

Mercury's magnetosphere

The Mariner 10 observations of Mercury's miniature magnetosphere collected during its close encounters in 1974 and 1975 are reviewed. Subsequent data analysis, re-interpretation and theoretical modeling, often influenced by new results obtained regarding the Earth's magnetosphere, have greatly expanded our impressions of the structure and dynamics of this small magnetosphere. Of special interest are the Earth-based telescopic images of this planet's tenuous atmosphere that show great variability on time scales of tens of hours to days. Our understanding of the implied close linkage between the sputtering of neutrals into the atmosphere due to solar wind and magnetospheric ions impacting the regolith and the resultant mass loading of the magnetosphere by heavy planetary ions is quite limited due to the dearth of experimental data. However, the influence of heavy ions of planetary origin (O⁺, Na⁺, K⁺, Ca⁺ and others as yet undetected) on such basic magnetospheric processes as wave propagation, convection, and reconnection remain to be discovered by future missions. The electrodynamic aspects of the coupling between the solar wind, magnetosphere and planet are also very poorly known due to the limited nature of the measurements returned by Mariner 10 and our lack of experience with a magnetosphere that is rooted in a regolith as opposed to an ionosphere. The review concludes with a brief summary of major unsolved questions concerning this very small, yet potentially complex magnetosphere.     

Cometary magnetospheres: a tutorial

The nucleus of an active comet, such as comet Halley near its perihelion, produces large quantities of gas and dust. The resulting cometary atmosphere, or coma, extends more than a million kilometers into space, where it interacts with the solar wind. An “induced” cometary magnetosphere is a consequence of this interaction. Cometary ion pick-up and mass loading of the solar wind starts to take place at very large cometocentric distances. Eventually this mass loading leads to the formation of a weak cometary bow shock. Even closer to the nucleus, collisional processes, such as ion-neutral chemistry, become important. Other features of the magnetosphere of an active comet include a magnetic barrier, a magnetotail, and a diamagnetic cavity near the nucleus. X-ray emission from comets is produced by the interaction of the solar wind with cometary neutrals and this topic is also discussed. A broad review of the cometary magnetosphere will be given in this paper.     

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.     

The response of the Hermean magnetosphere to the interplanetary magnetic field

The interaction between the solar wind and Mercury is anticipated to be unique because of Mercury’s relatively weak intrinsic magnetic field and tenuous neutral exosphere. In this paper the role of the IMF in determining the structure of the Hermean magnetosphere is studied using a new self-consistent three-dimensional quasi-neutral hybrid model. A comparison between a pure northward and southward IMF shows that the general morphology of the magnetic field, the position and shape of the bow shock and the magnetopause as well as the density and velocity of the solar wind in the magnetosheath and in the magnetosphere are quite similar in these two IMF situations. A Parker spiral IMF case, instead, produces a magnetosphere with a substantial north–south asymmetric plasma and magnetic field configuration. In general, this study illustrates quantitatively the role of IMF when the solar wind interacts with a weakly magnetised planetary body.     

X-ray, γ-emission and energetic particles in near-Earth space as measured by CORONAS-F satellite: From maximum to minimum of the last solar cycle

The Russian solar observatory CORONAS-F was launched into a circular orbit on July 31, 2001 and operated until December 12, 2005. Two main aims of this experiment were: (1) simultaneous study of solar hard X-ray and γ-ray emission and charged solar energetic particles, (2) detailed investigation of how solar energetic particles influence the near-Earth space environment. The CORONAS-F satellite orbit allows one to measure both solar energetic particle dynamics and variations of the solar particle boundary penetration as well as relativistic electrons of the Earth’s outer radiation belt during and after magnetic storms. We have found that significant enhancements of relativistic electron flux in the outer radiation belt were observed not only during strong magnetic storms near solar maximum but also after weak storms caused by high speed solar wind streams. Relativistic electrons of the Earth’s outer radiation belt cause volumetric ionization in the microcircuits of spacecraft causing them to malfunction, and solar energetic particles form an important source of radiation damage in near-Earth space. Therefore, the present results and future research in relativistic electron flux dynamics are very important.     

地球磁场对太阳风扰动响应的研究

分别对行星际激波、太阳风动压增大事件和减小事件的地球磁场响应进行了比较. 分析结果表明, 同步轨道磁场对太阳风扰动在向阳面产生较强的正响应, 在背阳面 响应较弱且有时会出现负响应, 地磁指数SYM-H对太阳风扰动的响应为正响应. 同时还得出, 向阳侧同步轨道磁场响应幅度d Bz与地磁指数响应幅度d SYM-H、上下游动压均方差均具有较好的相关性. 地磁指数响应幅度与同步轨道磁场响应幅度相关关系在激波和动压增大事件中具有一致性, 动压减小事件出 现明显差异, 这说明激波和动压增大事件在影响地球磁场方面具有某种共性.      

日侧外磁层ULF波调制EMIC波的MMS观测

磁层多尺度卫星(MMS-1)在日侧06:30 MLT(磁地方时,Magnetic Local Time)外磁层大于2Re(L为7.5～10.1)的范围内观测到多达21个波包的准周期性电磁离子回旋波(EMIC)事件.超低频(ULF)波和能量质子温度各向异性准周期性增强也被同步观测到.频率分析显示,ULF波的周期、质子各向...     

Solar wind dependence of the Pc1 wave activity

There are a host of factors influencing the excitation of Pc1 geomagnetic pulsations, which are ULF waves in the frequency range between 0.2 and 5 Hz. We have studied carefully the dependence of the pearl-type Pc1 activity at Sodankylä, Finland (L = 5.1) on the plasma density N in front of the magnetosphere, the bulk velocity V of the solar wind, and the intensity B of the IMF. The result is as follows: high values of N and reduced values of V are favorable to appearance of Pc1, whereas the dependence of Pc1 activity on B is practically absent. We also show that the probability of Pc1 occurrence decreases with the interplanetary electric field, and increases with solar wind impact pressure and with the plasma to magnetic pressure ratio “beta”.     

GEO轨道相对论电子日积分通量预报统计建模

基于辐射带相对论电子哨声波局地加速理论,将地磁AE指数作为源电子通量和通量各向异性的指标,将地磁Dst指数作为损失机制的指标,利用滑动窗口线性滤波器方法,建立了一个地球静止轨道大于2MeV相对论电子预报模型.利用该模型开展了2000-2009年地球静止轨道相对论电子通量预报试验.研究发现,这10年总预报效率为0.818,2003年的预报效率（0.633）最低,2009年的预报效率（0.856）最高.模型预报效果与持续模型相比有很大提高,略低于利用太阳风参数作为输入的同类预报模型的预报效果.这说明即使在缺少太阳风参数的情况下,该模型利用地磁扰动参数也能取得较好的预报效果.当模型输入参数增加了太阳风速度时,即综合考虑了行星际扰动和磁层扰动对辐射带粒子加速过程的影响,模型逐年的预报效率进一步提升.其中,2005年的预报效率提升了9.5%,这10年的总预报效率增加到0.848,预报值与实测值之间的线性相关系数为0.918,均方根误差为0.422.      

Ion-acoustic waves in unmagnetized collisionless weakly relativistic plasma of warm-ion and isothermal-electron using time-fractional KdV equation

Collisionless unmagnetized plasma consisting of a mixture of warm ion-fluid and isothermal-electron is considered, assuming that the ion flow velocity has a weak relativistic effect. The reductive perturbation method has been employed to derive the Korteweg–de Vries (KdV) equation for small – but finite-amplitude electrostatic ion-acoustic waves in this plasma. The semi-inverse method and Agrawal’s method lead to the Euler–Lagrange equation that leads to the time fractional KdV equation. The variational-iteration method given by He is used to solve the derived time fractional KdV equation. The calculations show that the fractional order may play the same rule of higher order dissipation in KdV equation to modulate the soliton wave amplitude in the plasma system. The results of the present investigation may be applicable to some plasma environments, such as space-plasmas, laser-plasma interaction, plasma sheet boundary layer of the earth’s magnetosphere, solar atmosphere and interplanetary space.     

Evolution of Dst index,cosmic rays and global temperature during solar cycles 20–23

We have studied conditions in interplanetary space, which can have an influence on galactic cosmic ray (CR) and climate change. In this connection the solar wind and interplanetary magnetic field parameters and cosmic ray variations have been compared with geomagnetic activity represented by the equatorial Dst index from the beginning 1965 to the end of 2012. Dst index is commonly used as the solar wind–magnetosphere–ionosphere interaction characteristic. The important drivers in interplanetary medium which have effect on cosmic rays as CMEs (coronal mass ejections) and CIRs (corotating interaction regions) undergo very strong changes during their propagation to the Earth. Because of this CMEs, coronal holes and the solar spot numbers (SSN) do not adequately reflect peculiarities concerned with the solar wind arrival to 1 AU. Therefore, the geomagnetic indices have some inestimable advantage as continuous series other the irregular solar wind measurements. We have compared the yearly average variations of Dst index and the solar wind parameters with cosmic ray data from Moscow, Climax, and Haleakala neutron monitors during the solar cycles 20–23. The descending phases of these solar cycles (CSs) had the long-lasting solar wind high speed streams occurred frequently and were the primary contributors to the recurrent Dst variations. They also had effects on cosmic rays variations. We show that long-term Dst variations in these solar cycles were correlated with the cosmic ray count rate and can be used for study of CR variations. Global temperature variations in connection with evolution of Dst index and CR variations is discussed.     

Qualitative estimation of magnetic storm efficiency in producing relativistic electron flux in the Earth’s outer radiation belt using geomagnetic pulsations data

It is well known that during many but not all of the geomagnetic storms enhanced fluxes of high-energy electrons are observed in the outer radiation belt. Here we examine relativistic (>2 MeV) electron fluxes measured by GOES at the synchronous orbit and on-ground observations of two types of ULF pulsations during 30 magnetic storms occurred during 1996–2000. To characterize the effectiveness of the chosen magnetic storms in producing relativistic electron fluxes, following to (Reeves, G.D., McAdams, K.L., Friedel, R.H.W., O’Brien, T.R. Acceleration and loss of relativistic electrons during geomagnetic storms. Geophys. Res. Lett. 30, doi:10.1029/2002GL016513, 2003), we calculate a ratio of the maximum daily-averaged electron flux measured during the recovery phase, to the mean pre-storm electron flux. A storm is considered an effective one if its ratio exceeds 2. We compare behavior of Pi1 and Pc5 geomagnetic pulsations during effective and non-effective storms and find a tendency for a storm efficiency to be higher when the mid-latitude Pi1 pulsations are observed for a long time during the magnetic storm main phase. We note also that the prolonged powerful Pc5 pulsation activity during the recovery phase of a magnetic storm is the necessary condition for the storm effectiveness. To interpret the found dependences, we suggest that there are two prerequisites for generating relativistic electron populations during a storm: (1) the availability of seed electrons in the magnetosphere, and Pi1 emissions are indicators of the mid-energy electron interaction with the ionosphere and (2) acceleration of the seed electrons to MeV energies, and interaction of electrons with the MHD wave activity in the Pc5 range is one of the most probable mechanisms proposed in the literature for this purpose.     

Solar wind and its interaction with the magnetosphere: Measured parameters

The earth's magnetosphere absorbs only a minor fraction (≈ 10^?3) of the incident solar wind energy. Variations of the solar wind can often cause lively reactions in the earth's close environment. However, the physical mechanisms involved are not yet understood. It appears now that the combined action of the solar wind momentum flux, the direction of the interplanetary magnetic field as well as its fluctuations might play the dominant role. The behaviour of these parameters is governed in some characteristic way by the solar wind stream structure which reflects the condition of the solar corona and its magnetic field topology. Transients in the sun's atmosphere associated with solar activity cause reactions in the interplanetary medium which also show some typical, though very different, signatures. Taking into account the interdependence of the solar wind parameters in context with the underlying solar phenomena, we may be able to pinpoint the mechanism which controls the action of the solar wind on the magnetosphere.     

Effects of man on geomagnetic activity and pulsations

Until recently the only known large-scale effects of man on geomagnetic activity and pulsations were those produced by high-altitude nuclear explosions. However, in just the last few years, measurements have indicated that changes can also be produced by (1) moderately-powered pulsed HF radio (1–20 MHz) transmissions into the ionosphere, (2) high-powered pulsed VLF radio transmissions (3–15 kHz) into the magnetosphere, and (3) by the ULF magnetic noise (frequencies < 5 Hz) from modern dc electric powered mass transit systems. Further, experiments reported by U.S. and Soviet scientists support the suggestion that ULF geomagnetic changes in the ionosphere and magnetosphere can be generated by the passage of a large ULF current around a peninsula in the sea. As a result of these experimental activities, it appears that controlled experiments using artificially generated ULF signals in the ionized upper atmosphere are now feasible. Finally, the report of a “weekend effect” in geomagnetic activity (as measured by the geomagnetic activity index Ap, for example) suggests that man's activities may already have been subtly influencing geomagnetic activity for many years, possibly because of the radiation from electric power distribution systems into the magnetosphere.