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1.
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
2.
Naoshi Fukushima 《Pure and Applied Geophysics》1989,131(3):437-446
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
3.
Spherical harmonic coefficients (SHCs) for the daily magnetic variation fields (solar and lunar) and the main field of the earth are usually estimated by the method of least squares applied to a truncated spherical harmonic series. In this paper, an integral method for computing the SHCs for the solar quiet daily magnetic variation fieldSq is described and applied toSq data for May and June 1965. TheSq SHCs thus derived are then compared with the results obtained using both unweighted and weighted versions of the least squares method. The weighting used tends to orthogonalize the least squares terms. The integral and weighted least squares results agree closely for terms up to order 4 and degree 30, but both disagree considerably for the higher degree terms with the results of the unweighted least squares. Errors introduced by the numerical integration can be shown to be small, hence the disagreement between integral and unweighted least squares coefficient sets arises from improper weighting. Also, it is concluded that discrepancies between the geomagnetic northward and eastward component-derived coefficient sets arise from either time-dependent external sources that produce non-local-time, based fields or nonpotential sources and not from truncation of the spherical harmonic series as has previously been suggested.Deceased. 相似文献
4.
G. K. Mukherjee 《Pure and Applied Geophysics》1987,125(5):845-852
The average latitude of theSq(X) focus along the longitude 75°E has been estimated using the Tsyganenko model (Tsyganenko, 1981) of the external magnetic field for storm time conditions of the magnetosphere. It is observed that the shift of the focal latitudes, due to magnetospheric currents, is only about 1 to 2° even during strong storms. It is also shown that the shift is asymmetric about the equator and longitude dependent. The day to day changes in observed focal position are much larger and the magnetospheric currents cannot, therefore, be regarded as a dominant mechanism of focal movement.The paper was presented at the IAGA General Assembly meeting held in Prague, Czechoslovakia, during August 1985. 相似文献
5.
V. V. Kalegaev 《Geomagnetism and Aeronomy》2011,51(7):855-865
A review of modern dynamic models of the Earth’s magnetosphere (the A2000 paraboloid model and Tsyganenko’s T01 model) is
presented. For the magnetic storm of January 9–11, 1997, the results of joint calculations of the magnetospheric magnetic
field are presented and contributions of the large-scale magnetospheric currents to the D
st variations are analyzed. Both models were shown to be well consistent with measurement data; the contribution of the magnetotail
current system to D
st is comparable to the contribution of the ring current. At the same time, the relative dynamics of magnetospheric current
systems are different in different models. The differences in the magnetic field variation profiles for various current systems
calculated by the A2000 and T01 models are explained by model parameterizations. 相似文献
6.
E. E. Antonova I. P. Kirpichev I. L. Ovchinnikov K. G. Orlova S. S. Rossolenko 《Geomagnetism and Aeronomy》2009,49(8):1172-1175
We consider a number of new approaches that arise when the topology of currents in the high-latitude magnetosphere is investigated.
We note that the high correlation between magnetospheric processes and solar wind parameters is a well-known feature of the
magnetospheric dynamics. The proposed explanations of the observed dependences run into difficulties related to the high level
of observed turbulence in the magnetosheath and inside the magnetosphere. The topology of the high-latitude magnetosphere
in the transition region from dipole magnetic field lines to those extending into the tail is also poorly known. We consider
the topology of transverse magnetospheric currents using satellite measurements of the plasma pressure distribution. The currents
of the nearest plasma sheet are shown to be closed inside the magnetosphere. The generation of field-aligned currents in Iijima
and Potemra region currents 1 and large-scale magnetospheric convection are discussed. 相似文献
7.
The contribution of global magnetospheric oscillations to magnetic disturbance during magnetospheric storms is studied. The
bases of magnetic data from the INTERMAGNET global network in combination with the interplanetary and intramagnetospheric
measurements of the magnetic field and plasma and the sets of the Kp, Dst, and AE indices are used for this purpose. The most favorable conditions in the solar wind and magnetosphere for generation of global
Pc5 have been revealed. The contribution of these oscillations to the variations in the magnetic disturbance level, characterized
by the AE index, has been estimated. The findings confirm that magnetospheric MHD oscillations participate in the processes of energy
income from the solar wind and energy dissipation in the magnetosphere. 相似文献
8.
The dynamics of the magnetospheric magnetic field during the magnetic storms of different intensity has been studied. The magnetic field variations on the Earth’s surface were calculated using the paraboloid model of the magnetosphere, taking into account the induction currents flowing in the diamagnetically conductive Earth. Dst and its components have been calculated for ten magnetic storms. It has been indicated that relative contributions of magnetospheric sources to Dst change depending on the storm power. For weak and moderate storms, the contribution of the magnetotail current sheet can reach values comparable with the ring current contribution and, sometimes, can even exceed this contribution. For strong storms, the ring current field dominates over the tail current field, the absolute value of which does not exceed 150 nT (also achieved during less intense storms). For storms with minimum Dst exceeding-200 nT, the tail current field is saturated, whereas the ring current can continue developing. 相似文献
9.
本文讨论了一种地球磁层的亚暴机制。当行星际磁场有大的南向分量时,磁层的位形可由基本闭式转变为开式。磁鞘中的阿尔文波可以携带超过10~(18)尔格/秒的能流传入磁层尾部,并将能量耗散于等离子体片中。等离子体片中的粒子被加热和加速后,注入近地空间,产生环电流和极区亚暴。计算了剪切流场中阿尔文波的传播过程,以及磁层中阿尔文波的耗散。将本文的结算与[4]中的结果合在一起,可以说明当行星际磁场转向南时,容易发生地球磁层亚暴,但这两者并非一一对应的关系,行星际磁场没有南向分量时也可以发生地球磁层亚暴。 相似文献
10.
The results of studying the distribution character of the amplitudes and time intervals between wave packets of Pi2 geomagnetic
pulsations, observed during the nighttime development of magnetospheric substorms and in the absence of these phenomena, have
been presented. The analog records from the midlatitude Borok Geophysical Observatory (geographic coordinates φ = 58.03°;
λ = 38.97°) for 1995 and 1997 have been used to analyze Pi2 pulsations. Three groups of pulsations have been analyzed: Pi2
observed during sub-storms related to the external impact on the magnetosphere, Pi2 spontaneously originating during substorms,
and Pi2 observed in the absence of substorms on the nightside of the magnetosphere. Interplanetary magnetic field B
y and B
z components and the solar wind dynamic pressure (ρV
2) have been considered as possible triggers of magnetospheric substorms. It has been indicated that the distributions of the
amplitude and the duration of time intervals between Pi2 bursts are approximated by the power and exponential functions, respectively,
which is typical of intermittent processes. The hypothesis that the processes of magnetospheric plasma turbulization can be
among the Pi2 pulsation burst sources has been put forward. It is assumed that the obtained characteristic values can be used
to qualitatively estimate the degree of plasma turbulence on the nightside of the magnetosphere when a sequence of Pi2 wave
packets is excited. 相似文献
11.
A. E. Levitin L. A. Dremukhina L. I. Gromova N. G. Ptitsyna 《Geomagnetism and Aeronomy》2014,54(3):300-307
The model calculation of a magnetic disturbance, which was registered at Colaba observatory (India) during the historic giant magnetic storm on September 1–2, 1859, is illustrated. The calculation demonstrates that the observed, unusually fast, 2-h main phase of this storm, when the negative amplitude of the geomagnetic field vector H component was ?1600 nT, and an extremely fast (1.5-h) initial field recovery phase from the maximum to the ?110 nT amplitude can be generated. The following models of the magnetospheric current systems were used in the calculations: the ring current (DR), the magnetospheric magnetopause current (DCF), the magnetotail current system (DT), and the high-latitude current system (DP). The unusual time variation in the registered geomagnetic disturbance is related to the probable fast and considerable equatorward shift of the high-latitude currents during the main phase of the analyzed giant storm and to the same fast backward motion of these currents during the initial field recovery phase. The unusually large amplitude of the registered geomagnetic disturbance could have been caused by the total contribution of the indicated magnetospheric current systems during the time when the storm was generated as a result of the interaction between the magnetosphere and the solar plasma ejected during the gigantic solar flare before the storm. 相似文献
12.
V. V. Kalegaev I. I. Alexeev E. V. Makarenkov N. Yu. Ganvushkina 《Geomagnetism and Aeronomy》2006,46(5):563-569
A unified method for calculating the Dst index and its components using models of the magnetospheric magnetic field is proposed. The method is consistent with the procedure for calculating Dst from the ground-based magnetometer data. When calculating Dst, the quiet-day magnetic variation is subtracted from the model variation of the magnetic field of magnetospheric sources. The effect of induced currents flowing in the surface layer of the Earth’s crust is taken into account. The dynamics of the magnetospheric current systems during a storm is studied based on an analysis of the Dst components. The magnetic field components for a “quiet” day in June 1998 are studied. The calculations of the Dst components in the parabolid and T01 models demonstrate that the maximum contributions of the ring current and magnetotail current system to the Dst variation are comparable for the magnetic storm of June 25–26, 1998. 相似文献
13.
本文讨论了赤道附近地球磁层中磁声重波沿重力场方向的传播特征。结果表明,当波动频率小于截止频率ωc时,磁声重波将在磁层中被反射。对于典型的磁层等离子体参数,ωc的极大值约为0.3秒-1。我们还讨论了磁声重波与地磁微脉动之间的关系,沿着重力场方向向下传播的磁声重波,可能直接引起赤道附近的Pc1磁脉动。 相似文献
14.
Willis L. Webb 《Pure and Applied Geophysics》1971,84(1):89-108
Summary The atmospheric electrical structure of the earth is postulated to be controlled by a motivating force in the lower ionosphere which is produced by interaction between neutral atmosphere tidal circulations and the ionospheric plasma in the presence of the earth's magnetic field. Associated electric fields power the dynamo currents through the Hall effect with a resulting development of a gross electric potential distribution in the lower ionosphere. Asymmetries in these hemispheric potential distributions result in exospheric current flows in lowL-shells and larger differences in potential produced by dynamo return current flows in high magnetic latitudes result in strong currents through highL-shells between auroral zones. Vertical thunderstorm currents with their associated lightning discharges effectively connect the earth to a low potential region of the dynamo circuit and thus supply the earth with an average negative charge which motivates a leakage tropospheric electrical circuit. In addition, the dynamo currents maintain the magnetic polar regions at different potentials with a resulting electrical exchange with the solar wind through the earth's near space. These considerations indicate that observed electrical and variable magnetic phenomena near the earth are all part of a single comprehensive electrical current system.This paper was read byH. Dolezalek in an abbreviated form supplied by the author. 相似文献
15.
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
16.
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
17.
L. V. Tverskaya 《Geomagnetism and Aeronomy》2011,51(1):6-22
The present-day state of the studies of the outer radiation belt relativistic electrons and the boundary of the solar proton
penetration into the magnetosphere during magnetic storms is briefly reviewed. The main attention is paid to the results from
studying the interrelation between these structural formations and other magnetospheric plasma structures. It has been indicated
that the relationship between the position of the maximum of belt of relativistic electrons injected during magnetic storms
(L
max) and the magnetic storm amplitude (|Dst|max = 2.75 × 104/L
max4) can be used to predict the extreme latitudinal position of such magnetospheric plasma formations as a trapped radiation
region boundary, the nighttime equatorial boundary of the auroral oval, and westward electrojet center during a storm. Using
the examples of still rare studies of the solar proton boundary dynamics in the magnetosphere based on the simultaneous measurements
on several polar satellites, it has been demonstrated that a change in the geomagnetic field topology during magnetic storms
can be diagnosed. 相似文献
18.
Cosmic ray (CR) fluxes, which penetrate into the Earth??s magnetosphere and atmosphere from the interplanetary space, are an important factor of space weather. The geomagnetic field allows or forbids CR particles to enter into a given point in the magnetosphere depending on their energy. The geomagnetic cutoff rigidity regulates the distribution of CR fluxes in the magnetosphere. The geomagnetic cutoff rigidity (geomagnetic threshold) determination accuracy is closely related to the accuracy of the magnetospheric model used in calculations. Using a method for tracing of charged CR particle trajectories in the magnetic field of a model magnetosphere, we obtained geomagnetic thresholds for two magnetosphere empirical models (Ts01 and Ts04), constructed based on the same initial database. The Ts01 model describes the middle magnetosphere for certain conditions in the solar wind and interplanetary field. The Ts04 model pays the main attention to describing the large-scale evolution of magnetospheric currents during a storm. The theoretically obtained geomagnetic thresholds have been compared with experimental thresholds, calculated using the spectrographic global survey method based on data from the global network of CR stations. The study has been performed for the period of a strong geomagnetic storm that occurred in November 2003. 相似文献
19.
C. A. Reddy 《Pure and Applied Geophysics》1989,131(3):485-508
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
20.
Summary A statistical investigation of the world-wide electric current-systems corresponding to s.c's has been carried out. The storm-time variationDst and the disturbance diurnal variationDs of s.c's are derived separately from the results of the average local-time variations in the magnetic field at different latitudes.A conspicuousDs current-system is found in the inner polar regions, and a concentrated current-flow is also confirmed along the geomagnetic equator resembling the current-system of an enhancedSq-field. The inner polar region currents flow towards the meridian at about 9h local-time and are supposed to complete their path along the outer auroral zone in opposite directions in the forenoon and afternoon hemispheres. It is of interest that the pattern of this atmospheric electric current-system is very similar to that caused by an electric doublet centred on the highiy conducting region near the pole.Some observed facts concerning the statistical nature of s.c's can be explained by these current-systems. 相似文献