共查询到20条相似文献，搜索用时 31 毫秒
1.
S.-I. Akasofu 《Planetary and Space Science》1982,30(4):389-393
It is suggested that the ionosphere plays an active role in many substorm processes by generating field-aligned currents associated with the Hall current. Various substorm phenomena, such as the cross-tail current interruption, the asymmetric main phase field and the poleward expanding auroral bulge, may be closely related to the closure of the Hall current circuits in the magnetosphere. 相似文献
2.
Kyoung W. Min 《Astrophysics and Space Science》1990,163(1):95-107
Magnetospheric substorm in the magnetotail region is studied numerically by means of a three-dimensional MHD code. The analytic solution for the quiet magnetotail is emloyed as an initial configuration. The localized solar wind is modeled to enter the simulation domain through the boundaries located in the magnetotail lobe region. As a result of the interaction between the solar wind and the magnetosphere, the magnetic field lines are stretched, and the plasma sheet becomes thinner and thinner. When the current-driven resistivity is generated, magnetic reconnection is triggered by this resistivity. The resulting plasma jetting is found to be super-magnetosonic. Although the plasmoid formation and its tailward motion is not quite clear as in the two-dimensional simulation, which is mainly because of the numerical model chosen for the present simulation, the rarification of the plasmas near thex-point is observed. Field-aligned currents are observed in the late expansive stage of the magnetospheric substorm. These field-aligned currents flow from the tail toward the ionosphere on the dawn side and from the ionosphere toward the tail on the dusk side, namely in the same sence of the region 1 current. As the field-aligned currents develop, it is found that the cross-tail current in the Earthside midnight section of the magneticx-point is reduced. 相似文献
3.
Walter J. Heikkila 《Solar physics》1983,88(1-2):329-336
It has been proposed that magnetospheric substorms and solar flares are a result of the same mechanism. In our view this mechanism is connected with the escape, or attempted escape, of energized plasma from a region of closed magnetic field lines bounded by a magnetic bottle. In the case of the Earth, it must be plasma that is able to maintain a discrete auroral arc, and we propose that the cross-tail current connected to the arc is filamentary in nature to provide the field-aligned current sheet above the arc. A localized meander of such an intense current filament could be caused by a tearing instability in the neutral sheet. Such a meander will cause an inductive electric field opposing the current change everywhere. In trying to reduce the component of the induction electric field parallel to the magnetic field lines, the plasma must enhance the transverse or cross-tail component; this action leads to eruptive behavior, in agreement with tearing theories. This enhanced induction electric field will cause a discharge along the magnetic neutral line at the apex of the magnetic arches, constituting an impulsive acceleration of all charged particles originally near the neutral line. The products of this phase then undergo betatron acceleration for a second phase. This discharge eventually reduces the electric field along the neutral line, and thereafter the enclosed magnetic flux through the neutral line remains nearly constant. The result is a plasmoid that has definite identity; its buoyancy leads to its escape. The auroral breakup (and solar flare) is the complex plasma response to the changing electromagnetic field. 相似文献
4.
It is assumed that the three-dimensional current system of a substorm passes three successive stages. (1) When a dawn-to-dusk magnetospheric electric field appears, a current system with field-aligned currents at the poleward boundary of the auroral zone arises. An equivalent ionospheric current system calculated, taking into account a day-night asymmetry of ionospheric conductivity, looks like the well-known DP-2 system including an eastward low-latitude current and a greater magnitude of the dusk vortex in comparison with the dawn one. (2) An electric drift of plasma towards the Earth leads to the appearance of a westward partial ring current increasing in time. This current is closed by field-aligned currents at the equatorward boundary of the auroral zone. The calculated equivalent current system is similar to the well-known one of the precursory phase. (3) An increase of the auroral ionospheric conductivity during the expansive phase produces an increase of all currents and a turning of field-aligned currents at the equatorward boundary of the auroral zone relative to those at the poleward one. The calculated equivalent current system is similar to the DP-1 system. 相似文献
5.
S. Matsushita 《Planetary and Space Science》1982,30(9):875-878
The mean electromotive force perpendicular to the mean current (Rädler effect) by random hydromagnetic waves in a collisionless plasma is derived. The results are applied to the field-aligned currents in the Earth's magnetotail. It is shown that the Rädler-effect electric field is large enough to give the observed value of the field-aligned currents and can be identified as a possible source for the field-aligned currents. 相似文献
6.
P.L. Israelevich I.M. Podgorny A.K. Kuzmin N.S. Nikolaeva E.M. Dubinin 《Planetary and Space Science》1988,36(12):1317-1328
Electric and magnetic fields and auroral emissions have been measured by the Intercosmos-Bulgaria-1300 satellite on 10–11 January 1983. The measured distributions of the plasma drift velocity show that viscous convection is diminished in the evening sector under IMF By < 0 and in the morning sector if IMF By > 0. A number of sun-aligned polar cap arcs were observed at the beginning of the period of strongly northward IMF and after a few hours a θ-aurora appeared. The intensity of ionized oxygen emission [O+(2P), 7320 Å] increased significantly reaching up to several kilo-Rayleighs in the polar cap arc. A complicated pattern of convection and field-aligned currents existed in the nightside polar cap which differed from the four-cell model of convection and NBZ field-aligned current system. This pattern was observed during 12 h and could be interpreted as six large scale field-aligned current sheets and three convective vortices inside the polar cap. Sun-aligned polar cap arcs may be located in regions both of sunward and anti-sunward convection. Structures of smaller spatial scale correspond to the boundaries of hot plasma regions related to polar cap arcs. Obviously these structures are due to S-shaped distributions of electric potential. Parallel electric fields in these S-structures provide electron acceleration up to 1 keV at the boundaries of polar cap arcs. The pairs of field-aligned currents correspond to those S-structures: a downward current at the external side of the boundary and an upward current at the internal side of it. 相似文献
7.
We have considered disturbances produced by a field-aligned current flowing through a thin layer with a finite conductivity along the magnetic field. The layer conductivity is an arbitrary function of transverse coordinates and time. It is shown that a suddenly emerging layer of the anomalous resistivity in the region of the auroral field-aligned currents leads to a generation of an Alfvén impulse with an amplitude up to 100 gammas. All electromagnetic disturbances appear to be localized inside the magnetic field tube passing through the anomalous resistivity region. An attempt to hinder the field-aligned current with an insulator does not stop the current, but forces it to flow round the insulator. 相似文献
8.
Electric fields and currents in the ionosphere generated by field-aligned currents observed by TRIAD
On the basis of the experimental data on the ionospheric conductivities and field-aligned currents the electric fields and currents in the ionosphere generated by the field-aligned currents were computated for various magnetic activity conditions. The model of the ionospheric conductivities by Vanyan and Osipova (1975) was used taking into account the influence of the universal time seasons and magnetic activity. The field-aligned current patterns and their change with magnetic activity was set on the basis of the TRIAD data. It is shown that the calculated patterns of the ionospheric electric fields and currents are in agreement with the measured electric fields and the equivalent current systems of the magnetic disturbances in high latitudes. The conclusion is made that the magnetospheric field-aligned currents are the main sources of the presently known polar magnetic disturbances. 相似文献
9.
《Planetary and Space Science》1987,35(6):759-768
A serendipitous event is reported in which the MAGSAT satellite intercepted an auroral arc over Svalbard, Norway where an all-sky television camera, a photographic camera and a meridian scanning photometer were making continuous measurements. The high time resolution of the optical measurements and the high spatial resolution of the magnetometer data are combined to investigate the relationship between the fine structure in the field-aligned current reversals and the temporal and spatial morphology of the auroral structure. Meridian scans of several optical emissions in the auroral arc, which had its upper portion in sunlight, are utilized to derive the total energy input and the intensity of the precipitating energetic electrons. The MAGSAT satellite apparently intercepted a fold within an extended intense upward current sheet. The current carried by the energetic electrons responsible for the optical aurora is found to be smaller than the field-aligned current derived from the magnetic perturbations, implying that there may be a large flux of low energy particles in this arc. Within the spatial-temporal constraints of this event there is a suggestion that the rayed structure is related to the field-aligned current reversals. 相似文献
10.
A numerical simulation method is used to show the possibility of forming a current sheet in the solar corona in an active region with four magnetic poles. The evolution of the quasi-stationary current sheet can lead to its transfer to an unsteady state. The MHD instability of this sheet causes its decay, accompanied by a set of events which characterizes the solar flare. The electrodynamical model of a solar flare includes a system of field-aligned currents typical of a magnetospheric substorm. Several events in substorms and solar flares are explained by the generation of field-aligned currents. 相似文献
11.
Zmuda and Armstrong (1974) showed that the field-aligned currents consist of two pairs; one is located in the morning sector and the other in the evening sector. Our analysis of magnetic records from the TRIAD satellite suggests that in each pair the poleward field-aligned current is more intense than the equatorward current, a typical ratio being 2:1. This difference has a fundamental importance in understanding the coupling between the magnetosphere and the ionosphere. We demonstrate this importance by computing the ionospheric current distribution by solving the continuity equation using the “observed” distribution of j∥ for several models of the ionosphere with a high conductive annular ring (simulating the auroral oval).It is shown that the actual field-aligned and ionospheric current system is neither a simple Birkeland type, Boström type nor Zmuda-Armstrong type, but is a complicated combination of them. The relative importance among them varies considerably, depending on the conductivity distribution, the location of the peak of the field-aligned currents, etc. Further, it is found that the north-south segment of ionospheric current which connects the pair of the field-aligned currents in the morning sector does not close in the same meridian and has a large westward deflection. Thus, it has an appreciable contribution to the westward electrojet. One of the model calculations shows that the entire north-south closure current contributes to the westward electrojet. 相似文献
12.
The location of field-aligned currents in the evening sector with respect to the auroral electrojets is examined. The tri-axial TRIAD satellite data and the simultaneous ground magnetometer data from along the Alaska meridian are analysed. It is shown that an intense upward fieldaligned current flows out from the region of the westward electrojet where discrete auroras are located. The downward flowing current exists in the region further equatorward, namely in the region of the eastward electrojet. However, the downward current is present even when there is no eastward electrojet. The boundary between the upward and the downward currents coincides, in most cases, with the boundary between the westward and the eastward auroral electrojets. Thus, the Harang discontinuity, a narrow area separating the positive and negative H bays, is the region where there is no field-aligned current. 相似文献
13.
W.-H. Ip 《Planetary and Space Science》1979,27(2):121-125
If the structure of the magnetic field and electric current in the cometary type I tail can be represented by an electric current circuit, disruption of the cross-tail current system may lead to a current discharging through the cometary ionosphere, and the dissipation of the magnetic energy stored in the tail. From the point of view of energy budget, a tail-aligned magnetic field on the order of 10γ will be sufficient to produce a strong ionization effect of the cometary atmosphere. 相似文献
14.
Y. Nakagawa 《Astrophysics and Space Science》1990,174(1):91-94
The physical conditions needed for the development of field-aligned force-free current in astrophysical circumstances are considered. It is shown that a large-scale differential motion of magnetic regions can lead to the development of magnetic field with the preferential enhancement of force-free current. Other physical consequences of force-free current in evolving magnetic field are also discussed. 相似文献
15.
The release of plasma in the jovian magnetotail is observed in the form of plasmoids, travelling compression regions, field-aligned particle beams and flux-rope like events. We demonstrate that electrons propagate along the magnetic field lines in the plasma sheet boundary layer (PSBL), while close to the current sheet center the electron distribution is isotropic. The evidences of the counterstreaming electron beams in the PSBLs are also presented. Most of the field-aligned energetic ion beams are associated with the field-aligned electron beams and about half of them have the bipolar fluctuation of the meridional magnetic field component. Moreover they often show a normal velocity dispersion for the different species which fits well in the scenario of particle propagation from a single source. All features above are observed during jovian reconfiguration events which are typically bonded with plasma flow reversals. From all these characteristics, which are based on energetic particle and magnetic field measurements, we believe that the reconfiguration processes in the jovian magnetotail are associated with reconnection. 相似文献
16.
The discrepancy between the overhead E-region current and the magnetic D-component is studied using data obtained by the Chatanika incoherent scatter radar (L = 5.6). The F-region horizontal current is estimated to be too small to cause the observed D-deflection. Also, the assumption that the magnetic effects of the Pedersen and field-aligned currents cancel each other on the ground is shown to be inadequate to solve the problem. The significance of the inclination angle in the data analysis and the importance of the field-aligned current sheets are discussed. 相似文献
17.
Field-aligned currents in the day-time cusp-region are regarded as the superposition of various current sheets under the influence of different solar wind parameters. The principal feature of this pattern is a specific region 3 of field-aligned currents located poleward of region 1 and affected by both the azimuthal and northward components of the interplanetary magnetic field. It is shown that recent measurements carried out on the TRIAD satellite (Saflekos and Potemra, 1979) unambiguously point to the existence of region 3. The data on the transverse magnetic disturbances supplied by S3-2 satellite (Doyle et al., 1981) accord with our model on taking into account the relations between the IMF parameters and the field-aligned current intensity. 相似文献
18.
Equivalent ionospheric current systems representing IMF sector effects on the geomagnetic field in high latitudes are examined for each of the twelve calendar months by spherical harmonic analyses of geomagnetic hourly data at 13 northern polar stations for seven years. The main feature of obtained equivalent current systems includes circular currents at about 80° invariant latitude mostly in the daytime in summer and reversed circular currents at about 70° invariant latitude mainly at night in winter. Field-aligned current distributions responsible for equivalent currents, as well as vector distributions of electric fields and ionospheric currents, are approximated numerically from current functions of equivalent current systems by taking assumed distributions of the ionospheric conductivity. Two sets of upward and downward field-aligned current pairs in the auroral region, and also a field-aligned current region near the pole show seasonal variations. Also, ionospheric electric-field propagation along geomagnetic field lines from the summer hemisphere to the winter hemisphere with auroral Hall-conductivity effects may provide an explanation for the winter reversal of sector effects. 相似文献
19.
Electrostatic waves excited by a field-aligned electron current sheet of finite thickness are investigated. The finite width of the current sheet gives rise to boundary conditions to be satisfied at the sheet edge. This results in a restriction to the number of modes which may be driven unstable. Ducted and evanescent mode solutions are obtained. It is shown that the finite thickness of the current sheet partially stabilizes the system and contributes to the coherence of the excited waves. 相似文献
20.
We propose a model three-dimensional current system for the magnetospheric substorm, which can account for the new findings of the field-aligned and ionospheric currents obtained during the last few years by using new techniques. They include (1) the ionospheric currents at the auroral latitude deduced from the Chatanika incoherent scatter radar data, (2) the field-aligned currents inferred from the vector magnetic field observations by the TRIAD satellite and (3) the global distribution of auroras with respect to the auroral electrojets appearing in DMSP satellite photographs. The model current system is also tested by a computer model calculation of the ionospheric current pattern. It is shown that the auroral electrojets have a strong asymmetry with respect to the midnight meridian. The westward electrojet flows along the discrete aurora in the evening sector, as well as along the diffuse aurora in the morning sector. The eastward electrojet flows equatorward of the westward electrojet in the evening sector. It has a northward component and joins the westward electrojet by turning westward across the Harang discontinuity. Thus, the latitudinal width of the westward electrojet in the morning sector is much larger than that in the evening sector. The field-aligned currents, consisting of two pairs of upward and inward currents (one is located in the morning sector and the other in the evening sector), are closed neither simply by the east-west ionospheric currents nor by the north-south currents, but by a complicated combination of the north-south and east-west paths in the ionosphere. The magnetospheric extension of the current system is also briefly discussed. 相似文献