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1.
From a study of thunder/lightning observations in Trivandrum (near dip equator) for selected years between 1853 and 2005, we could find an inverse relation of the same with sunspot activity and associations with enhancements in diurnal range of local geomagnetic declination. The results seem to suggest lightning-associated modulation of E-region dynamo currents in the equatorial ionosphere and the thunderstorm activity near dip equator probably acts as a moderator to regulate electric potential gradient changes in the global electric circuit due to solar activity changes.  相似文献   

2.
By using Tsyganenko's model for the magnetosphere's magnetic field, which links two hemispheres of the ionosphere, and adopting a practical boundary condition for the electric potential around the polar cap, we developed a new ionosphere–magnetosphere coupling model based on prairie view dynamo code (PVDC). The new model takes the variations in solar wind and interplanetary magnetic field, as well as the geomagnetic activity, into account. Rather than the previous version of PVDC that is useful only for quiet conditions, the new model enables to calculate the electric potential and currents in the ionosphere and the field-aligned current (FAC) off the ionosphere in quiet and disturbed times. Comparison of the calculated FAC with the measurements of Space Technology 5 (ST5) mission shows a good agreement.  相似文献   

3.
Summary Stewartson [1]2) has considered the inviscid flow past a sphere in the presence of a uniform magnetic field andMurray andLudford [2] have investigated a similar problem in which the magnetic field originates from an axially symmetric dipole field situated at the centre of the sphere. In connection with the study of earth's magnetic field, the toroidal part of this field plays a dominant part. This gives rise to the importance of studying the effect of a toroidal magnetic field on flows past different bodies of revolution; specially past spheres and spheroids. In the present note inviscid flows past a sphere, and a spheroid, are considered, for the case of a toroidal magnetic field originating in the fluid. In the case of the sphere the field inside the sphere consists of an electric dipole directed along the axis of symmetry together with a uniform electric field which produces a uniform current along the axis. In the case of the spheroid, the field inside it is due to an electric dipole and quadrupole directed along the axis of symmetry, together with a uniform electric field which produces a uniform current along this axis.  相似文献   

4.
The spatial distributions of electric fields and currents in the Earth’s atmosphere are calculated. Electric potential distributions typical of substorms and quiet geomagnetic conditions are specified in the ionosphere. The Earth is treated as a perfect conductor. The atmosphere is considered as a spherical layer with a given height dependence of electrical conductivity. With the chosen conductivity model and an ionospheric potential of 300 kV with respect to the Earth, the electric field near the ground is vertical and reaches 110 Vm−1. With the 60-kV potential difference in the polar cap of the ionosphere, the electric field disturbances with a vertical component of up to 13 V m−1 can occur in the atmosphere. These disturbances are maximal near the ground. If the horizontal scales of field nonuniformity are over 100 km, the vertical component of the electric field near the ground can be calculated with the one-dimensional model. The field and current distributions in the upper atmosphere can be obtained only from the three-dimensional model. The numerical method for solving electrical conductivity problems makes it possible to take into account conductivity inhomogeneities and the ground relief.  相似文献   

5.
Since the discovery of the magnetosphere, it has been known that the currents flowing in the magnetosphere contribute toSq, the regular daily variation in the earth's surface magnetic field. The early models, however, were not very accurate in the vicinity of the earth. The magnetospheric contribution toSq has therefore been recalculated by direct integration over the three major magnetospheric current systems; magnetopause, tail and ring. The finite electrical conductivity of the earth, which increases the horizontal and decreases the vertical components of the magnetospheric field at the earth's surface, has been taken into account. The magnetospheric currents are found to contribute 12 nanotesla to the day to night difference in the mid-latitudeSq pattern for steady, quiet magnetospheric conditions. They also contribute to the annual variation in the surface field and must be considered an important source of the observed day to day variation in theSq pattern.  相似文献   

6.
If the earth and its ionosphere are immersed in a large-scale dawn-to-dusk electric field (of the order of 0.5 mV/m), the resultant dawn-to-dusk ionospheric currents are much stronger on the dayside than on the nightside. These asymmetric currents over the earth produce a magnetic field detectable on the ground, which will contribute to a considerable extent to theSq-field and equatorial electrojet.This paper was presented at the IAGA General Assembly meeting (Session 9.1) held in Vancouver, Canada, during August 1987.  相似文献   

7.
Three-dimensional structures of the ionospheric dynamo currents are examined using the neutral winds in a general circulation model of the middle atmosphere at Kyushu University. A quasi-three-dimensional ionospheric dynamo model is constructed assuming an infinite parallel conductivity in the ionosphere. This model is able to simulate both the equatorial electrojet and the global Sq current system successfully. The simulated results reveal that the equatorial electrojet is confined in quite narrow latitudes around the equator accompanied with meridional current circulations and satisfies a non-divergent structure mainly within the E region. A vertically stratified double layered structure is seen in the east–west current density near the focus latitude of the global Sq current system. It is shown that the stratified structure mainly consists of the east–west Hall current associated with the eastward wind of zonal wavenumbers 1 and 2 in the lower altitudes and the westward wind of zonal wavenumber 2 in the upper altitudes. The day-to-day variation of the neutral winds can significantly vary the induced ionospheric dynamo current system, which is recognized as changes of the focus latitude and/or the maximum value of the equatorial electrojet.  相似文献   

8.
The problem of the penetration of nonstationary ionospheric electric fields into the lower atmospheric layers is considered based on the model of the global electric circuit in the Earth’s atmosphere. For the equation of the electric field potential, a solution that takes into account exponential variation in the electrical conductivity with height has been obtained. Analysis of the solution made it possible to reveal three cases of the dependence of the solution on height. The first case (the case of high frequencies) corresponds to the Coulomb approximation, when the electrical conductivity of the atmosphere can be neglected. In the case of low frequencies (when the frequency of changes in the ionosphere potential is less than the quantity reciprocal to the time of electric relaxation of the atmosphere), a quasi-stationary regime, in which the variation in the electric potential of the atmosphere is determined by the electric conduction currents, occurs. In the third case, due to the increase in the electrical conductivity of the atmosphere, two spherical regions appear: with the Coulomb approximation in the lower region and conduction currents in the upper one. For these three cases, formulas for estimating the electric field strength near the Earth’s surface have been obtained.  相似文献   

9.
On days that are quiet with respect to solar-terrestrial activity phenomena, the geomagnetic field has variations, tens of gamma in size, with major spectral components at about 24, 12, 8, and 6 hr in period. These quiet daily field variations are primarily due to the dynamo currents flowing in theE region of the earth's ionosphere, are driven by the global thermotidal wind systems, and are dependent upon the local tensor conductivity and main geomagnetic field vector. The highlights of the behavior and interpretation of these quiet field changes, from their discovery in 1634 until the present, are discussed as an introduction to the special journal issue on Quiet Daily Geomagnetic Fields.  相似文献   

10.
Modelling of space weather effects on pipelines   总被引：1，自引：0，他引：1  
The interaction between the solar wind and the Earth's magnetic field produces time varying currents in the ionosphere and magnetosphere. The currents cause variations of the geomagnetic field at the surface of the earth and induce an electric field which drives currents in oil and gas pipelines and other long conductors. Geomagnetically induced currents (GIC) interfere with electrical surveys of pipelines and possibly contribute to pipeline corrosion.In this paper, we introduce a general method which can be used to determine voltage and current profiles for buried pipelines, when the external geoelectric field and the geometry and electromagnetic properties of the pipeline are known. The method is based on the analogy between pipelines and transmission lines, which makes it possible to use the distributed source transmission line (DSTL) theory. The general equations derived for the current and voltage profiles are applied in special cases. A particular attention is paid to the Finnish natural gas pipeline network.This paper, related to a project about GIC in the Finnish pipeline, thus provides a tool for understanding space weather effects on pipelines. Combined with methods of calculating the geoelectric field during magnetic storms, the results are applicable to forecasting of geomagnetically induced currents and voltages on pipelines in the future.  相似文献   

11.
The morphology of slowly-varying geomagnetic external fields (such as Sq, L, and Dst) and the production mechanisms of electric current systems for those fields are briefly reviewed to provide background knowledge of the present state of research regarding the source fields for scientists concerned with the electromagnetic induction within the earth. It is concluded that both the Sq and Dst fields seem to have sources both in the magnetosphere and the ionosphere, while the classic idea of L-field production solely in the ionosphere by the wind dynamo is still acceptable.  相似文献   

12.
The distribution of the electric potential, generated by the magnetospheric field-aligned currents flowing along the auroral oval and in the dayside cusp region at the upper atmospheric boundary in the polar ionosphere, is calculated. The obtained electric potential distributions are used to calculate the electric field strength near the Earth’s surface. The results of the model calculations are in good agreement with the electric field measurements at Vostok Antarctic station. It has been indicated that large-scale magnetospheric fieldaligned currents, related to IMF variations, can affect variations in the electric field strength in the polar regions via changes in the electric potential in the polar ionosphere, associated with these currents.  相似文献   

13.
Polar regionSq     
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   

14.
在地理坐标系下推导出二维电离层发电机理论方程,采用逐线迭代法求解得到全球二维电离层发电机电流函数,进而得到电离层发电机电流和电场.模式中使用的电导率是根据外部经验模式给出的背景大气和电离层参数,采用理论公式计算得出;输入的中性风场和磁场分别由HWM93和IGRF2000模型给出,该电离层发电机理论模式很好地给出了全球Sq电流形态及电离层E层发电机电场的基本特征.利用该模式研究了外部模式风场以及地磁场随高度的变化对模拟结果的影响,发现在90~180 km高度上,风场随高度变化对电流影响较大,而地磁场影响较小;重点模拟研究了地磁平静时期,Sq电流涡旋中心位置和总电流强度的变化规律,初步研究发现,电流中心位置在地理纬度±30°附近,不同的地方时电流随地磁纬度线平行移动,且南北半球两个电流涡中心电流强度之和变化不大.分析发现这种规律与发电机高度上的磁场总强度及地磁倾角的全球分布有很好的相关性.  相似文献   

15.
Modeling the ionosphere wind dynamo: A review   总被引：4，自引：0，他引：4  
This paper reviews the current status of research concerned with modeling the ionospheric wind dynamo. Simulation models have been reasonably successful in reproducing the types of magnetic perturbations that are produced by the dynamo. Ionospheric electric fields are less well simulated, particularly at night. The primary areas of research needed to improve our ability to simulate realistically the ionospheric wind dynamo are in the modeling of nighttime conditions, hemispherical asymmetries of thermospheric tides, and mutual dynamic coupling among winds, conductivities, electric fields, and electric currents.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

16.
Ionospheric two-stream waves and gradientdrift waves nonlinearly drive a large-scale (D.C.) current in the E-region ionosphere. This current flows parallel to, and with a comparable magnitude to, the fundamental Pedersen current. Evidence for the existence and magnitude of wave-driven currents derives from a theoretical understanding of E-region waves, supported by a series of nonlinear 2D simulations of two-stream waves and by data collected by rocket instruments in the equatorial electrojet. Wave-driven currents will modify the large-scale dynamics of the equatorial electrojet during highly active periods. A simple model shows how a wave-driven current appreciably reduces the horizontally flowing electron current of the electrojet. This reduction may account for the observation that type-I radar echoes almost always have a Doppler velocity close to the acoustic speed, and also for the rocket observation that electrojet regions containing gradientdrift waves do not appear also to contain horizontally propagating two-stream waves. Additionally, a simple model of a gradient-drift instability shows that wavedriven currents can cause nonsinusoidal electric fields similar to those measured in situ.  相似文献   

17.
The magnetosphere and ionosphere are coupled into a power circuit by field-aligned currents. If there were only Hall current in the ionosphere, the problem of magnetosphere-ionosphere interaction would not have arisen. Field-aligned currents could be seen as emerging as a result of the break in the magnetospheric current across the tail, since the Hall current is divergence-free and does not perform any work. In fact, the current in the ionosphere is complex. It always has a Pedersen component, and the ionosphere is a real energy consumer. Together with energy, an extrinsic electrical current should flow into the ionosphere. The current coming from the generator in front of the bow shock is a part of the extrinsic current. The aim of this paper is to generalize the previously obtained partial solution to the problem of magnetosphere-ionosphere interactions in the region of auroral electrojets, also taking into account the generation of the extrinsic current in front of the bow shock.  相似文献   

18.
本文讨论了行星际磁场B2分量变化时内磁层和中低纬度电离层的响应.指出B2变化引起的磁层大尺度对流电场的变化在一定条件下有可能透入内磁层,并沿磁力线映射到中低纬度电离层,在那里产生电场和电流体系,从而使Sq电流体系发生畸变,并在地面磁场中反映出来.数值计算表明,当△B2<0时,Sq电流体系的焦点向东和向高纬移动,地面磁场会观测到数伽马的变化.这就为中低纬地磁观测诊断磁层和太阳风状态提供了一种可能性.此外,本文还用上述物理过程解释了赤道地区一些高空物理现象,如B2倒转时电离层漂移速度的变化,赤道磁场异常以及赤道q型偶现E层的消失等等.  相似文献   

19.
A model for the coast-effect of geomagnetism is presented, in which the horizontal magnetic field induces currents in a circuit including a thin finite ocean. The currents flow horizontally across the ocean, vertically down into the earth, back through the deep interior of the earth, and vertically up to the ocean to complete the current loop. The upper layers of the earth are given non-zero conductivity, allowing the possibility of such current loops.A two-dimensional model involving such currents has been worked out analytically, and it is found that a significant induced magnetic field at the seafloor can be obtained with a reasonable conductivity in the earth's upper layers. A three-dimensional model has also been worked out numerically. It is found that the induced vertical component of magnetic field is of comparable magnitude to the horizontal component induced normal to the coast, whereas the horizontal component parallel to the coast is small. These relations are required to explain the observation of Parkinson arrows.  相似文献   

20.
The typical quiet day variations of the equatorial electrojet (EEJ) current intensity with time of the day, season, sunspot number, and geomagnetic latitude are presented in terms of the corresponding variations of H which is the deviation of the horizontal component (H) of the geomagnetic field from its steady nighttime level. The observed height structure of the current density in the EEJ as measured in rocket flights is presented, along with the theoretically computed structure. Theoretical model results on the polarization electric fields and east-west currents as generated by the local interactions of height-varying winds in the EEJ show large height gradients and reversals for both currents and electric fields; experimental evidence for the reality of such height structures is also shown. The characteristics of the counter-electrojet events are presented and the possible causative mechanisms are discussed critically.Some typical experimental results are presented on the electric field changes in the EEJ which result from its sensitive response to electrodynamic disturbances in the magnetosphere and the auroral-polar latitude ionosphere during geomagnetic substorms and storms; and their implications are discussed. Possibilities for utilizing the EEJ as a very useful medium for important scientific studies on the larger space domain of ionosphere-magnetosphere system, on plasma waves, and on the earth's conductivity are emphasized.  相似文献   

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