磁暴主相期间环电流分布特性模拟研究

磁暴主相期间对流电场驱动等离子体片中的能量粒子经历E×B漂移，被地磁场俘获形成环电流，在此理论基础上充分考虑电荷交换造成的环电流损失与离子沉降的影响，改善并验证了磁暴主相期间环电流离子分布模式.模拟了不同强度磁暴主相期间磁层环电流离子的分布特征，研究了部分环电流离子对对流电场的响应.结果表明：不对称的环电流是磁暴主相期间环电流的重要组成部分，其分布特性表现为晨昏不对称和日夜不对称以及离子投掷角分布的各向异性等.对流电场与能量离子通量强度和分布范围之间正相关.模拟结果与观测有很好的一致性，证明了模型的可行性 关键词： 部分(不对称)环电流 磁暴主相 离子通量分布 对流电场     

Electric field and field-aligned currents produced by asymmetric ring current

The formation of the problem concerning calculation of the electric field and field-aligned currents in the magnetosphere and ionosphere produced by asymmetric ring current is considered with the approach and equations developed by [1–3]. These equations were used previously for estimation of the electric field in the ionosphere and magnetosphere appearing in the process of spreading of energetic particles injected into the trapping zone of the magnetosphere as a result of nuclear explosion. According to this theory, energetic particles injected into a ring current produce an asymmetric divergent ring current, field-aligned currents, a global electric field and currents in the ionosphere. Space Research Center, Polish Academy of Sciences, Warsaw, Poland. Published from Izvestiya Vysshikh. Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 4, pp. 423–431, April, 1998.     

Structure of the magnetic field of the Jovian magnetosphere

We exactly solved the problem of the interaction between the rotating magnetic field of Jupiter and the equatorial plasma disk formed by the gases flowing from the Jovian satellite Io. The disk is shown to expel the Jovian magnetic field in both directions, inward, toward Jupiter, compressing its dipole magnetic field, and outward. Jupiter spins up the disk up to velocities that correspond to nearly constant angular rotation, but with an angular frequency lower than the angular frequency of Jupiter itself. The radial velocity of the plasma in the disk approaches its azimuthal velocity. We determined the power of Jupiter’s rotational energy losses. Part of this energy is transferred to the disk, and the other part goes into heating the Jovian ionosphere. We show that the Pedersen surface conductivity of the Jovian ionosphere must have a lower limit to maintain the electric current that arises in the disk-rotating magnetic field system. This current in the Jovian magnetosphere flows only along the preferential magnetic surfaces that connect the inner and outer edges of the disk to the ionosphere.     

Magnetosphere-Ionosphere Interactions-Near-Earth Manifestations of the Plasma Universe

As the universe consists almost entirely of plasma, the understanding of astrophysical phenomena must depend critically on our understanding of how matter behaves in the plasma state. In situ observations in the near-earth cosmical plasma offer an excellent opportunity for gaining such understanding. The near-earth cosmical plasma not only covers vast ranges of density and temperature, but is the site of a rich variety of complex plasma physical processes which are activated as a result of the interactions between the magnetosphere and the ionosphere. The geomagnetic field connects the ionosphere, tied by friction to the earth, and the magnetosphere, dynamically coupled to the solar wind. This causes an exchange of energy and momentum between the two regions. The exchange is executed by magnetic-field-aligned electric currents, the so-called Birkeland currents. Both directly and indirectly (through instabilities and particle acceleration) these also lead to an exchange of plasma, which is selective and therefore causes chemical separationi. Another essential aspect of the coupling is the role of electric fields, especially magnetic-field-aligned ("parallel") electric fields, which have important consequences both for the dynamics of the coupling and, especially, for energization of charged particles.     

The effect of plasma drift on the electromagnetic cyclotron instability

It is shown that the drift of plasma across a homogeneous magnetic field causes the generation of a wave electric field which, for waves propagating along the magnetic field in the whistler mode, is in the direction of the magnetic field. This leads to Landau damping of the wave field by the background electron distribution, simultaneously with amplification via the electromagnetic cyclotron instability. The drift velocity of the plasma for zero net growth of a whistler mode signal is calculated. It is suggested that such a process occurs in the equatorial region of the magnetosphere during a geomagnetic storm and accounts for the missing band of emissions at half the equatorial gyrofrequency.     

The ionosphere as a load on the global atmospheric electrical circuit

Low-frequency electric-mode excitation in the earth-ionosphere cavity is considered with the aid of Maxwellequation vector mode transformation with allowance for field penetration into the ionosphere and magnetosphere. It is shown that for atmospheric current generators, the ionosphere can exhibit the properties of a conductor or an insulator, depending, on frequency. The penetration of atmospheric electric fields from the earth into the ionosphere can cause corresponding unitary variatary variations of geophysical parameters.     

The solar wind interaction with the Earth's magnetosphere: atutorial

The size of the terrestrial magnetosphere is determined by the balance between the solar wind dynamic pressure and the pressure exerted by the magnetosphere, principally that of its magnetic field. The shape of the magnetosphere is additionally influenced by the drag of the solar wind, or tangential stress, on the magnetosphere. This drag is predominantly caused by the mechanism known as reconnection in which the magnetic field of the solar wind links with the magnetic field of the magnetosphere. The factors that control the rate of reconnection of the two fields are not understood completely, but a southward direction of the interplanetary field is critical to enabling reconnection with the dayside low-latitude magnetosphere, resulting in magnetic flux transfer to the magnetotail. Numerical simulations suggest that the conductivity of the ionosphere controls the rate of reconnection, but this has not been verified observationally. Although solar wind properties ultimately control the interaction, the properties of the plasma that make direct contact with the magnetosphere are different than those of the solar wind, having been altered by a standing bow shock wave. This standing shock is necessitated by the fact that the flow velocity of the solar wind far exceeds the velocity of the compressional wave that diverts the solar wind around the Earth. The upper atmosphere is the final recipient of all the energy and momentum that enters the magnetosphere. Coupling takes place along the magnetic field Lines principally in the polar and auroral region via current systems that close across the magnetic field both at low and high altitudes and flow parallel to the magnetic field between high and low altitudes     

Modeling of field-aligned currents produced by asymmetric ring current during strong magnetic storms

The modeling of field-aligned currents (FACs) produced by an asymmetric ring current is presented. Our first results of the modeling of FACs in the magnetosphere, which were based on the theory advanced in [1–5], were obtained in [6]. It was shown that FACs develop as spiral structures. Extending this work, we came to the conclusion that FACs, appearing in the magnetosphere and ionosphere as a result of ion or electron injections, generally develop as clockwise (ion injections) or anticlockwise (electron injections) spirals that are independent of the number and energy spectra or space distributions of injected particles. A sharp maximum of FACs or an FAC jet in such spirals can be present at middle latitudes. The value of currents in a midlatitudinal FAC jet during strong magnetic storms and substorms could be of the same order as experimentally observed in the polar region. The model presented describes the dependence of ion FACs as well as FAC jets in the magnetosphere and ionosphere, on the parameters of injected particles. Space Research Center, Polish Academy of Sciences, Warsaw, Poland. Published in Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 5, pp. 551–566, May, 1998.     

Thermal effects on parallel resonance energy of whistler mode wave

In this short communication, we have evaluated the effect of thermal velocity of the plasma particles on the energy of resonantly interacting energetic electrons with the propagating whistler mode waves as a function of wave frequency and L-value for the normal and disturbed magnetospheric conditions. During the disturbed conditions when the magnetosphere is depleted in electron density, the resonance energy of the electron enhances by an order of magnitude at higher latitudes, whereas the effect is small at low latitudes. An attempt is made to explain the enhanced wave activity observed during magnetic storm periods.     

Identification of Radial Distance of Plasma Dispersionless Injection Boundary from the Injection Source

Measurements of energetic particles obtained by the two geosynchronous satellites （1991-080 and LANL-97A） are performed to investigate the plasma injection boundary and source region during the magnetospheric substorms. The measurement method is developed to allow remote sensing of the plasma injection time and the radial distance of injection boundaries by using measured energy dispersion and modelling particle drifts within the Volland-Stern electric field and the dipole magnetic field model. The radial distance of the injection boundary deduced from a dispersion event observed by the LANL-97A satellite on 14 June 1998 is 7.1RE, and the injection time agrees well with the substorm onset time identified by the Polar Ultraviolet Imager. The method has been applied to an event happened at 22.9 UT on 11 March 1998, when both the satellites （1991-080 and LANL-97A） observed the dispersionless character. The results indicate that the radial distance of injection source locates at 8.1RE at magnetotail, and particles move earthward from magnetotail into inner magnetosphere at 22.5 UT.     

The electrojet phenomenon

The term ‘electrojet’ is frequently used to describe the intense bands of electric curent which flow at certain times in the earth's ionosphere at an altitude of about 100 km. Two main forms of electrojet current are distinguished; an equatorial electrojet which flows during the daylight hours in a narrow band of latitudes centred on the magnetic equator, and an auroral electrojet which flows during the main phese of magnetic storms in auroral regions. Both are accompanied by abnormally large changes in the geomagnetic field components as measured at the earth's surface. This article reviews the main features of the two forms of electrojet and discusses the present theories for their origin. Ionospheric irregularities are associated with both types of electrojet, and the experimental evidence so far accumulated indicates that these are produced by plane plasma waves generated by a two-stream instability in the plasma and travelling with the acoustic velocity of about 360 m s^?1.     

Poynting flux impulses and the ionospheric switching of geomagnetic substorms

Observations were made of impulse events in Poynting flux calculated from electric and magnetic disturbances encountered by the Polar satellite when on high-latitude field-lines in the magnetotail. These were found to be coincident within±6 min with impulsive spikes in cosmic radio background absorption in the D region of the ionosphere as detected by the Imaging Riometer for Ionospheric Studies riometer in Finland. They were also coincident with substorm onset at the same geomagnetic latitude as determined by a change of gradient in International Monitor for Auroral Geomagnetic Effects’ X-component magnetograms. The interpretation of the observations was that magnetospheric compression waves from the geomagnetic equator region of the magnetotail were coupling to progressively initiate field-guided Alfvén shear waves towards higher geomagnetic latitudes over a large volume of the magnetosphere. The study suggested that they were then able either directly or indirectly to ionise the D region of the ionosphere and in the process to cut deep electrically conducting channels between the magnetosphere and the ionosphere through which currents could flow and initiate the characteristic signature of geomagnetic substorms in ground magnetograms.     

Magnetospheric dynamics during the storm of February 14, 2009

The structure of the magnetic field in the magnetospheric during the storm of February 14, 2009 is studied. The model parameters that characterize the magnetospheric magnetic field are calculated every hour on the basis of solar wind data and the evolution of the magnetic field during the storm is reproduced using the A2000 model of the Earth’s magnetosphere. It is shown that extremely quiet geomagnetic conditions in 2009 promoted the expansion of the magnetosphere and were favorable for the formation of magnetic-island-like structures (plasmoids) in the geomagnetic tail. It is ascertained that negative variations in the B_z component could occur in the nightside magnetosphere in situations where the magnetic flux through the tail lobes exceeded certain thresholds, which depend on the parameters of the magnetospheric current systems. It is shown that the formation of magnetic islands decreases the magnetic flux through the tail lobes and prevents excessively strong development of the magnetic field in the tail.     

Comparing the geomagnetic thresholds of cosmic rays for two empirical models of the magnetosphere during the period of an extreme geomagnetic storm in November 2003

The accuracy of determining the geomagnetic cutoff rigidity (the geomagnetic threshold) is closely related to that of describing the magnetic field of the magnetosphere with the model used for calculations. Geomagnetic thresholds are calculated for two empirical models of the magnetosphere, Ts0l and Ts04, constructed on the basis of the same initial experimental data. The Ts01 model describes the average magnetosphere for certain conditions in the solar wind and interplanetary field. The Ts01 model focuses on describing the large-scale evolution of magnetospheric currents during a storm. A comparison of the geomagnetic thresholds for Ts0l and Ts04 with experimental thresholds calculated by the Spectrographic Global Survey from data of the CR global network stations shows that the Ts01 model describes the magnetic field of the magnetosphere more realistically. Our study was conducted for the period of a strong geomagnetic storm in November 2003.     

Earthquakes and global electrical circuit

Based on recent experimental and theoretical model results, the role of earthquakes and processes of their preparation as electricity sources in the global electric circuit (GEC) is discussed. In addition to the traditional elements of the GEC, such as thunderstorm currents, ionosphere currents, fair weather currents, and telluric currents, hypothetical seismogenic currents flowing between the faults and the ionosphere are considered. The ionization sources for these currents are presumably the radiation of radioactive gases and the ionization by the electric field of so-called “positive holes” created by the compression of tectonic plates, whereas transportation of electric charges between the Earth and the ionosphere occurs under the action of electric fields and turbulent diffusion (for heavy charged species). Seismogenic currents deliver electric charges into the ionosphere, which give rise to electric fields in it and in the magnetically conjugated region. The drift of magnetized plasma in the ionosphere F2-region and plasmasphere plasma under the action of these fields causes disturbances in the electron density and total electron content (TEC) of the ionosphere, which are observed by GPS satellites before strong earthquakes. The typical features of these disturbances (magnitudes, dimensions, stability, nighttime predominance of the relative TEC disturbances, geomagnetic conjugacy) are well reproduced in theoretical model calculations based on the solution of the equation for the electric ionosphere potential with specified seismogenic electric current at the lower boundary of the ionosphere if this current is strong enough (comparable with thunderstorm currents). The feasibility of such seismogenic currents is discussed. It is argued that the TEC disturbances observed before strong earthquakes cannot be explained by neutral atmosphere disturbances. These TEC disturbances can be treated as ionospheric earthquake precursors created by seismogenic GEC disturbances.     

Electric current control of creation and annihilation of sub-100 nm magnetic bubbles examined by full-field transmission soft X-ray microscopy

The effect of electric current pulses on a sub-100 nm magnetic bubble state in a symmetric Pt/Co multilayer was directly observed using a full-field transmission soft X-ray microscope (MTXM). Field-induced evolution of the magnetic stripe domains into isolated bubbles with their sizes down to 100 nm was imaged under varying external magnetic fields. Electric current pulses were then applied to the created magnetic bubbles, and it was observed that the bubbles could be either created or annihilated by the current pulse depending on the strength of applied magnetic field. The results suggest that the Joule heating plays a critical role in the formation and/or elimination of the bubbles and skyrmions. Finally, the schematic phase diagram for the creation and annihilation of bubbles is presented, suggesting an optimized scheme with the combination of magnetic field and electric current necessary to utilize skyrmions in the practical devices.     

Axisymmetric particle-in-cell simulations of diamagnetic-cavityformulation in vacuum

Axisymmetric simulations of the expansion of a hot plasma suddenly introduced into a vacuum containing a weak magnetic field were performed using an electromagnetic particle-in-cell code. Both uniform and gradient fields have been used, with the simulation axis along the principal field direction. The formation of a diamagnetic cavity requires an initial plasma β>1; as the expansion proceeds, β diminishes, and the field eventually recovers. The maximum spatial extent of the cavity and its duration can be obtained from simple dynamical considerations. Field-aligned ion acceleration behind the electron front is observed in all field geometries and strengths. In the case of expansion into a divergent field, the plasma is found to move down the field gradient by ambipolar diffusion. These simulations are relevant to active release experiments in the Earth's magnetosphere, to pellet ablation experiments, and to the naturally occurring diamagnetic bubbles observed at the Earth's foreshock     

Characteristics of Polar Wind Flows at Altitudes of about 20000 km

The problem of the outflow of ionospheric plasma into the magnetosphere is considered. In particular, the phenomenon of the polar wind observed in the polar cap is studied. The study of this phenomenon is complicated by the fact that the field-alined velocities of individual ions are small, and therefore, the electric field of the positively charged satellite prevents their measurement. This paper examines the measurements carried out on the Interball-2 satellite at altitudes of ~20000 km and compares them with the results of simulations within the framework of the GSM TIP model. It has been demonstrated the GSM TIP model well describes the outflow of H⁺ ions from the ionosphere to the magnetosphere in the polar cap.     

Core plasmas in space weather regions

In recent years, there has been strong interest in “space weather,” owing to increasing recognition of the myriad effects that such phenomena may have on space and even ground systems of considerable importance to man. The authors describe the presence of “core” plasmas in the ionosphere and magnetosphere, which may influence various space weather phenomena. Core plasmas are defined as plasmas with energies from zero to 50 eV (Horowitz, Rev. Geophys., 1987) and originating in the terrestrial ionosphere. They first describe the ionosphere as the basic core plasma region for the overall magnetosphere-ionosphere system. They then describe the principal inner/middle magnetospheric regions-the plasmasphere, ring current, and plasma sheet regions-and how core plasmas from the ionosphere, either with little or with substantial energization, become major components of these magnetospheric regions, which are prime “space weather” regions