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1.
Parameters of field-aligned currents reconstructed by ground-based measurements of magnetic field in the Scandinavian countries (IMAGE) and ionospheric conductivity for specific events of the 6 and 8 December 2004 are represented here. Ionospheric conductivity was calculated from precipitating electron flux measured at DMSP-13 satellite and electron density EISCAT incoherent scattering radar direct measurements. There is a high correlation between field-aligned currents, calculated from DMSP-13 satellite data and field-aligned currents calculated from radar measurements for the December 6, 2004 in the presence of developed ionospheric current system. The comparison of field-aligned currents, reconstructed by the proposed method, with the currents calculated by the variation of magnetic field on the DMSP satellites, confirms correctness of the offered algorithm. 相似文献
2.
磁暴的发生与环电流的变化密切相关.除了对称环电流外,部分环电流在磁暴的发展过程中也起到了重要的作用,同时部分环电流通过场向电流与极区电离层中的电流形成回路.本文应用INTERMAGNET地磁台网北半球中低纬区域地磁台站数据,对不同强度4个磁暴事件主相和恢复相期间部分环电流和场向电流的磁地方时分布进行了分析和讨论.对于每一个磁暴事件,在低纬地区（地磁纬度约0°—40°N）选用地磁经度上大致均匀的8个台站,通过坐标转换计算平行于磁偶极轴的地磁场水平分量H来分析磁暴期间环电流所引起的磁场扰动;在低纬地区8个台站的基础上增加中纬地区（地磁纬度约40°N—60°N）地磁经度上大致均匀的6个台站,计算地磁坐标系下地磁场东西分量Y来分析磁暴期间场向电流在中低纬地区引起的磁场扰动.结果表明,磁暴主相期间的部分环电流主要作用于磁地方时昏侧和夜侧扇区,并且主相和恢复相期间部分环电流引起的磁场变化随着磁暴级别的增大而增大;磁暴主相期间向下的场向电流多出现在夜侧至晨侧扇区,向上的场向电流多出现在昏侧至午后扇区,且中纬地区向下和向上场向电流的展布范围明显大于低纬地区;恢复相期间弱、中磁暴事件的场向电流呈现与部分环电流相同的减弱趋势,而强、大磁暴事件在恢复相末期场向电流引起的磁场变化明显不同于恢复相的其他时刻,这可能与高纬较强的亚暴活动有关. 相似文献
3.
The electrodynamic flare model is based on numerical 3D simulations with the real magnetic field of an active region. An energy
of ∼1032 erg necessary for a solar flare is shown to accumulate in the magnetic field of a coronal current sheet. The thermal X-ray
source in the corona results from plasma heating in the current sheet upon reconnection. The hard X-ray sources are located
on the solar surface at the loop foot-points. They are produced by the precipitation of electron beams accelerated in field-aligned
currents. Solar cosmic rays appear upon acceleration in the electric field along a singular magnetic X-type line. The generation
mechanism of the delayed cosmic-ray component is also discussed. 相似文献
4.
Wen-Yao Xu 《Pure and Applied Geophysics》1989,131(3):371-393
Geomagnetically quiet day variations in the polar region are reviewed with respect to geomagnetic field variation, ionospheric plasma convection, electric field and current. Persistently existing field-aligned currents are the main source of the polar regionSq. Consequently, the morphology and variability of the polar regionSq largely depend upon both field-aligned currents and ionospheric conductivity. Since field-aligned currents are the major linkage between the ionosphere and the magnetosphere, the latter is controlled by solar wind state, in particular, the interplanetary magnetic field, the polar regionSq exhibits remarkable IMF dependence. 相似文献
5.
The effects of the dayside and dusk plumes of the plasmasphere during the ring current recovery phase on the disturbance level
of the ground geomagnetic field horizontal component have been considered. It has been indicated that the geomagnetic field
horizontal component changes specifically and synchronously in the region corresponding to the plasmaspheric dayside plume.
Outside the plume the time variations in the geomagnetic field horizontal component pronouncedly differs. A spectral analysis
of disturbances in the geomagnetic field horizontal components in the range of geomagnetic pulsations indicated that the intensity
in the range of Pc4 pulsations increases at magnetic stations located on field lines corresponding to the dayside and dusk
plumes of the plasmasphere. These pulsations detected in the dynamic spectrum of the geomagnetic field horizontal components
in the dayside plume region of the plasmasphere, probably reflect the resonance oscillations of magnetic field lines in the
region of field-aligned currents at comparatively low altitudes. We assume that this is caused by the instability of field-aligned
currents originating as a result of the interaction between the ring current energetic ions and electromagnetic waves in the
region with a relatively dense background plasma of the dayside plume. 相似文献
6.
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． 相似文献
7.
Fluid theories explain the origin of region-2 field-aligned currents as the closure of the ring current, driven itself by the azimuthal pressure gradients generated in the magnetospheric ring plasma by the sunward convection. Although the structure of pressure gradients appears experimentally complex, observations confirm that a close connection exists between the region-2 field-aligned currents and the ring current. The fluid linear theory of the adiabatic transport by convection of the ring plasma gives a first estimate of this process, and leads ultimately to phase quadrature (in terms of magnetic local time) between the region-2 field-aligned currents and the convection potential. When significant non-adiabatic processes are taken into account, such as precipitations at auroral latitudes, the theoretical phase difference rotates toward opposition. We determine experimentally the phase relationship between the region-2 field-aligned currents and the convection potential from recent statistics, depending on the magnetic activity index Kp, and performed from the EISCAT data base. For geometrical reasons of sufficient probing of region 2, it is only computed in the case of a moderate magnetic activity corresponding to 2\leqKp<4. Region-2 field-aligned currents are found to be in phase opposition with the convection electrostatic potential at auroral latitudes. This confirms the importance of non adiabatic processes, especially ion losses, in the generation of region-2 field-aligned currents, as theoretically suggested. 相似文献
8.
根据Cluster卫星在中高度极尖区的观测数据,分析研究了两次连续磁暴期间极尖区场向电子事件的持续时间以及与Dst值和Dst时间变化率之间的关系.结果表明,磁暴期间场向电子事件的持续时间的范围为6~54 s,大多数场向事件的持续时间小于34 s;极尖区场向电子事件的最大密度和最大场向通量与Dst值没有明显的相关关系;而随着Dst变化率的增加,场向电子最大密度和最大通量也随之增加,场向电子最大密度与Dst变化率之间的相关系数为0.81,场向电子最大通量与Dst变化率之间的相关系数为0.56,下行电子最大通量与Dst变化率之间的相关系数为0.85.经讨论认为行星际磁场持续南向、太阳风速度和动压的急剧增加是引起场向电子通量增加的主要原因. 相似文献
9.
We have used the global numerical model of the coupled ionosphere-thermosphere-protonosphere system to simulate the electric-field, ion- and electron-temperature and -concentration variations observed by EISCAT during the substorm event of 25 March 1987. In our previous studies we adopted the model input data for field-aligned currents and precipitating electron fluxes to obtain an agreement between observed and modelled ionospheric variations. Now, we have calculated the field-aligned currents needful to simulate the substrom variations of the electric field and other parameters observed by EISCAT. The calculations of the field-aligned currents have been performed by means of numerical integration of the time-dependent continuity equation for the cold mag-netospheric electrons. This equation was added to the system of the modelling equations including the equation for the electric-field potential to be solved jointly. In this case the inputs of the model are the spatial and time variations of the electric-field potential at the polar-cap boundaries and those of the cold magnetospheric electron concentration which have been adopted to obtain the agreement between the observed and modelled ionospheric variations for the substorm event of 25 March 1987. By this means it has been found that during the active phase of the substorm the current wedge is formed. It is connected with the region of the decreased cold magnetospheric electron content travelling westwards with a velocity of about 1 km s–1 at ionospheric levels. 相似文献
10.
In this paper we study an instability of the plasma moving towards the Earth near the inner plasma sheet boundary. We include both the interchange instability of the plasma sheet and the magnetosphere-ionosphere interaction instability caused by an effect of field-aligned currents (connected with electron precipitation) on ionospheric conductivity. The instability leads to the separation of steady-state magnetospheric convection into parallel layers. This instability may be responsible for the appearance of quiet auroral arcs inside region 2 of field-aligned currents flowing out of the ionosphere. This instability allows us to explain also the existence of crossing auroral arcs. 相似文献
11.
对Ⅱ区场向电流及其伴随的部分环电流和电离层电流组成的内磁层三维电流体系（PRFI电流系）的磁场效应进行了数值计算.这一三维电流体系在中低纬度地面产生的磁场呈现出特殊的纬度分布:X分量几乎不随纬度变化,Y分量随纬度增高近似呈线性变化.这些特征明显不同于对称环电流的磁场分布特征（X∝ cosφ,φ是纬度,Y=0）,也不同于DP2、Sq、L等电流体系的磁场分布特征.利用这一特征我们可以从地磁台子午链观测到的磁场扰动中分离出PRFI电流系的贡献.用1989年3月磁暴的实例检验了上述模型,观测结果与理论结果符合得很好.分析结果还表明,最大的Dst指数并不一定对应着最强的对称环电流. 相似文献
12.
The works in the alternative direction of magnetospheric studies are reviewed. In contrast to the traditional approach, where the basis process is magnetic field line reconnection, transformation of kinetic energy into electromagnetic one at the bow shock front is the basis process in the proposed approach. It has been indicated that this new paradigm makes it possible to overcome the main difficulties that remained within the scope of the previous paradigm. It has been briefly demonstrated how several following processes and phenomena are explained within the scope of the new approach: (1) transformation of the solar wind kinetic energy into the electromagnetic energy; (2) electromagnetic energy transfer into the magnetosphere; (3) organization of the system of bulk currents, formation of field-aligned currents from the magnetosphere, and compatibility of these currents with the ionospheric current systems; (4) shape, value, and dynamics of the particle precipitation auroral regions; and (5) substorm expansion (auroral breakup). Other possibilities of the new approach and paradigm replacement consequences are briefly considered. 相似文献
13.
E. E. Grigorenko R. Koleva L. M. Zelenyi J. -A. Sauvaud 《Geomagnetism and Aeronomy》2010,50(6):720-732
We present an analysis of two crossings of the plasma sheet boundary layer (PSBL) in Earth’s magnetotail by a quartet of Cluster
satellites, accomplished both in the absolutely quiet geomagnetic interval and in the restoration period between two substorms.
It is found that in the quiet period, field-aligned electric currents were not observed in the PSBL, in spite of presence
in this region of high-velocity ions moving toward Earth along the magnetic field lines at velocities of ∼1400 km/s. This
means that in the given event, ions and electrons moved together; i.e., high-velocity ions were a part of the accelerated
plasma flow. In the disturbed period, the Cluster satellites detected a system of two oppositely directed field-aligned currents,
which can be associated with the presence of the X line rather close to the Earth. Owing to multipoint Cluster observations, we managed to estimate the spatial size of a current
structure (along the normal to the PSBL surface), which was equal, for a current flowing toward Earth along the high-latitude
PSBL boundary, to about 1600 km, which is comparable with the value of the inertial radius of ions. This agrees with the scenario
of spatial separation of charges and formation of the Hall system of currents in the magnetic reconnection region. The duration
of observation of the given current structure was ∼12 min., which points to the quasi-steady-state character of reconnection. 相似文献
14.
A statistical study of field-aligned electron beams associated with upflowing ion conics is presented from Exos-D (Akebono) observations below 10 000 km. The electron beams are narrowly collimated along the field line and generally have energies of several tens of eV. They are divided in the analysis into three types: upflowing, downflowing, and counterstreaming. All the types of electron beams are almost equivalent in their energy and pitch angle characteristics and their association rate with upflowing ion events. About 50% of ion conies are found to be coincident with field-aligned electron beams. There is also a correlation in energy between the field-aligned electrons and ion conics. These show that the association is not a mere coincidence but rather that the field-aligned acceleration of electrons is related to the perpendicular energization of ions. The association rate of upflowing electrons is high on the nightside, while that of downflowing electrons is high on the dayside. The association rate of downflowing electrons is high at low altitudes, and the rates of the three types of electron beams become equivalent at high altitudes. Data indicate that the height of the electron acceleration region is lower on the nightside. It is suggested that the average height of the electron acceleration region is around the satellite apogee (–10000 km), and the average thickness of the region is about thousands km. 相似文献
15.
The M flare that arises after magnetic field emersion in a small spot is analyzed. The disturbance, which propagated downwards and generated a source of acoustic waves (sunquake), was simultaneous with an outburst of hard X-radiation. The reasons of such sunquakes are discussed. Rearrangement of the magnetic configuration in the analyzed event is confirmed: field lines and strong currents at low altitudes above the polarity boundary line are transformed into the currents along the system of loops oriented at wide angles to the neutral line. This rearrangement occurred in the proximity of a small region (sigmoid) presumably identified by the location of the primary pulse energy release. In this case, there was no development of a high-energy sigmoid flare with the formation and ejection of large-scale magnetized ropes. Apparently, this was hindered by the nonstationarity of the phenomena at this activity center with a magnetic field of composite topology and multiple flare-generating centers. 相似文献
16.
Göran Marklund Lars Blomberg Carl-Gunne Fälthammar Per-Arne Lindqvist Lars Eliasson 《Annales Geophysicae》1995,13(7):704-712
High-resolution measurements by the double probe electric field instrument on the Freja satellite are presented. The observations show that extremely intense (up to 1 V m−1) and fine-structured (<1 km) electric fields exist at auroral latitudes within the altitude regime explored by Freja (up to 1700 km). The intense field events typically occur within the early morning sector of the auroral oval (01-07 MLT) during times of geomagnetic activity. In contrast to the observations within the auroral acceleration region characterized by intense converging electric fields associated with electron precipitation, upward ion beams and upward field-aligned currents, the intense electric fields observed by Freja are often found to be diverging and located within regions of downward field-aligned currents outside the electron aurora. Moreover, the intense fields are observed in conjunction with precipitating and transversely energized ions of energies 0.5-1 keV and may play an important role in the ion heating. The observations suggest that the intense electric field events are associated with small-scale low-conductivity ionospheric regions void of auroral emissions such as east-west aligned dark filaments or vortex streets of black auroral curls located between or adjacent to auroral arcs within the morningside diffuse auroral region. We suggest that these intense fields also exist at ionospheric altitudes although no such observations have yet been made. This is possible since the height-integrated conductivity associated with the dark filaments may be as low as 0.1 S or less. In addition, Freja electric field data collected outside the auroral region are discussed with particular emphasis on subauroral electric fields which are observed within the 19–01 MLT sector between the equatorward edge of the auroral oval and the inner edge of the ring current. 相似文献
17.
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. 相似文献
18.
Joachim Vogt 《Surveys in Geophysics》2002,23(4):335-377
Auroral phenomena are controlled by the geomagnetic field.Since the terrestrial field lines connect the auroral oval to the equatorial region at large distances, the collisionless plasma in this remote space environment can act as a power supply for the high-latitude upper atmosphere where auroral emissions take place. The coupling process is intimately linked to currents which flow across the local magnetic field direction both in the equatorial part and at the atmospheric end of the auroral field lines. These two auroral key regions are connected through currents flowing along the terrestrial field lines, thereby completing the auroral current circuit. Such field-aligned currents are carried by Alfvén waves, that is, magnetohydrodynamic shear waves, which are thus a means to exchange momentum and energybetween rather remote parts of the geomagnetically controlledspace environment. Auroral dynamics is further affected by a third key region in the auroral current circuit, namely the auroral acceleration region, where parallel electric fields accelerate particle to keV energies. This review focuses on key region coupling through Alfvén waves. Continuity requirements for currents and electric fields provide a convenient means to describe the interaction of Alfvén waves with different plasma regimes. Basic coupling aspects can be demonstrated with the help of a simplified model. Inhomogeneities and nonlinear feedback can lead to resonance effects and instabilities. 相似文献
19.
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. 相似文献
20.
J.-A. Sauvaud P. Koperski T. Beutier H. Barthe C. Aoustin J. J. Thocaven J. Rouzaud E. Penou O. Vaisberg N. Borodkova 《Annales Geophysicae》1997,15(5):587-595
The Toulouse electron spectrometer flown on the Russian project INTERBALL-Tail performs electron measurements from 10 to 26 000 eV over a 4 solid angle in a satellite rotation period. The INTERBALL-Tail probe was launched on 3 August 1995 together with a subsatellite into a 65° inclination orbit with an apogee of about 30 RE. The INTERBALL mission also includes a polar spacecraft launched in August 1996 for correlated studies of the outer magnetosphere and of the auroral regions. We present new observations concerning the low-latitude boundary layers (LLBL) of the magnetosphere obtained near the dawn magnetic meridian. LLBL are encountered at the interface between two plasma regimes, the magnetosheath and the dayside extension of the plasma sheet. Unexpectedly, the radial extent of the region where LLBL electrons can be sporadically detected as plasma clouds can reach up to 5 RE inside the magnetopause. The LLBL core electrons have an average energy of the order of 100 eV and are systematically field-aligned and counterstreaming. As a trend, the temperature of the LLBL electrons increases with decreasing distance to Earth. Along the satellite orbit, the apparent time of occurrence of LLBL electrons can vary from about 5 to 20 min from one pass to another. An initial first comparison between electron-and magnetic-field measurements indicates that the LLBL clouds coincide with a strong increase in the magnetic field (by up to a factor of 2). The resulting strong magnetic field gradient can explain why the plasma-sheet electron flux in the keV range is strongly depressed in LLBL occurrence regions (up to a factor of 10). We also show that LLBL electron encounters are related to field-aligned current structures and that wide LLBL correspond to northward interplanetary magnetic field. Evidence for LLBL/plasma-sheet electron leakage into the magnetosheath during southward IMF is also presented. 相似文献