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1.
We derive the expression for the ponderomotive force in the real multicomponent magnetospheric plasma containing heavy ions. The ponderomotive force considered includes the induced magnetic moment of all the species and arises due to inhomogeneity of the traveling low-frequency electromagnetic wave amplitude in the nonuniform medium. The nonlinear stationary force balance equation is obtained taking into account the gravitational and centrifugal forces for the plasma consisting of the electrons, protons and heavy ions (He+). The background geomagnetic field is taken for the dayside of the magnetosphere, where the magnetic field have magnetic “holes” (Antonova and Shabansky in Geomagn. Aeron. 8:639, 1968). The balance equation is solved numerically to obtain the nonlinear density distribution of ions (H+) in the presence of heavy ions (He+). It is shown that for frequencies less than the helium gyrofrequency at the equator the nonlinear plasma density perturbations are peaked in the vicinity of the equator due to the action of the ponderomotive force. A comparison of the cases of the dipole and dayside magnetosphere is provided. It is obtained that the presence of heavy ions leads to decrease of the proton density modification.  相似文献   

2.
We investigate analytically and numerically a nonlinear modification of the magnetospheric plasma density under the action of the ponderomotive force induced by ULF traveling waves, using the nonlinear stationary force balance equation. This equation is applied to both the dipole and dayside magnetosphere having one and two minima of the geomagnetic field near the magnetospheric boundary. The separate and joint actions of the ponderomotive, centrifugal, and gravitational forces on the density distribution are shown.  相似文献   

3.
A laboratory experiment is designed to study the interaction of the solar wind with the geomagnetic field. Time-exposure and time-resolved photographs are taken when plasma hits a model Earth, and direct measurements are made of the magnetic field change, plasma density and electric current distribution. The shape of the magnetic cavity formed on the upstream side of the model Earth is almost the same as that calculated for the geomagnetic cavity. The charged particles, which penetrate the magnetic cavity formed on the upstream side of the model Earth with east-west asymmetry from the neutral points on the cavity surface, appear to concentrate towards the equator on the rear side of the model, forming a westward electric current belt within the magnetosphere. When the dipole axis is not perpendicular to the plasma gun—magnetic dipole line, the invasion of plasma is more pronounced at the cusp of the cavity nearer to the gun. Charged particles appear to penetrate to a greater extent if a uniform external magnetic field is applied parallel to the magnetic dipole than if one is applied antiparallel.  相似文献   

4.
Simultaneous magnetic field data from the geostationary satellites GOES 2 and GOES 3 have shown significant differences between the inclination angles measured at these two satellites. The relationship between the two inclination angles is examined for three magnetic activity groups and eight local time sectors by using data from GOES 2 and GOES 3 for the 12-month period from March 1979 to February 1980. During this time GOES 2 was 1.09 RE off the geomagnetic equator in the northern geomagnetic hemisphere, while GOES 3 was separated from GOES 2 by 2 h L.T. and 0.47 RE off the geomagnetic equator, also in the northern geomagnetic hemisphere. The average inclination angle is found to differ substantially from the predictions based on the previously published magnetic field models. The relationship between the two inclination angles is fitted by a simple model of magnetic field perturbation that varies as a power of distance from the Equator. During magnetic disturbances, the spatial variation of magnetic field perturbation on the nightside suggests that the ring current density increases with distance from the geomagnetic equator.  相似文献   

5.
In order to investigate Pc3-4 geomagnetic pulsations at very low and equatorial latitudes, L=1.0 to 1.2, we analyzed simultaneous geomagnetic data from Brazilian stations for 26 days during October-November 1994. The multitaper spectral method based on Fourier transform and singular value decomposition was used to obtain pulsation power spectra, polarization parameters and phase. Eighty-one (81) simultaneous highly polarized Pc3-4 events occurring mainly during daytime were selected for the study. The diurnal events showed enhancement in the polarized power density of about 3.2 times for pulsations observed at stations close to the magnetic equator in comparison to the more distant ones. The phase of pulsation observed at stations near the magnetic equator showed a delay of 48-62° in relation to the most distant one. The peculiarities shown by these Pc3-4 pulsations close to the dip equator are attributed to the increase of the ionospheric conductivity and the intensification of the equatorial electrojet during daytime that regulates the propagation of compressional waves generated in the foreshock region and transmitted to the magnetosphere and ionosphere at low latitudes. The source mechanism of these compressional Pc3-4 modes may be the compressional global mode or the trapped fast mode in the plasmasphere driving forced field line oscillations at very low and equatorial latitudes.  相似文献   

6.
Forced magnetic reconnection induced by magnetohydrodynamic (MHD) waves may account for the triggering of explosive solar activities such as flares. Reconnection in a neutral sheet plasma can be driven by the ponderomotive force associated with nonlinear MHD waves accompanying plasma vortex motion. The nonlinear stage of forced reconnection by MHD waves is simulated with a MHD particle-code: Some conditions for fast reconnection are discussed with applications to solar flares.  相似文献   

7.
The paper describes the phenomenon of afternoon depression of the geomagnetic H field on quiet days near the magnetic equator in the Indian zone. These events occur most frequently around 1600 solar hr and are localized in longitude; sometimes, not seen at stations separated by even 2 hr LT. The geomagnetic disturbance tends to decrease or destroy the identity of the phenomenon. The latitudinal extent of these events is confined to the equatorial electrojet region. The events do not seem to be caused mainly by the Moon, but their occurrences are modified by the lunar age, being most frequent around new and full Moon. These events are associated with the disappearance of the q type of Es over the Equator for periods during which the H field is below the night-time level. The currents responsible for these events flow westward in the E-region and are within few degrees centred near the magnetic equator.  相似文献   

8.
本文研究了磁流体力学与高频等离子体波（ 包括纵横模式） 之间的精巧的相互作用。研究表明,这些等离激元会在电流片内诱发一种阻抗不稳定,并最终导至磁重联,出现爆发性不稳定。在高涨的离声湍动情况下,高温电流片模型必须采用反常电导率,而非库仑电导率。理论估算的结果与观测相一致。因此这种计及等离激元有质动力作用的新磁重联理论,基本上能解释耀斑现象。  相似文献   

9.
Some new ideas on the interaction of the solar wind with the magnetosphere are brought forward. The mechanism of reflection of charged particles at the magnetopause is examined. It is shown that in general the reflection is not specular but that a component of momentum of the particle parallel to the magnetopause changes. A critical angle is derived such that particles whose trajectories make an angle less than it with the magnetopause enter the magnetosphere freely, so transferring their forward momentum to it. Spatially or temporally non-uniform entry of charged particles into the magnetosphere causes electric fields parallel to the magnetopause which either allow the free passage of solar wind across it or vacuum reconnection to the interplanetary magnetic field depending on the direction of the latter. These electric fields can be discharged in the ionosphere and so account qualitatively for the dayside agitation of the geomagnetic field observed on the polar caps. The solar wind wind plasma which enters the magnetosphere creates (1) a dawn-dusk electric field across the tail (2) enough force to account for the geomagnetic tail and (3) enough current during disturbed times to account for the auroral electrojets. The entry of solar wind plasma across the magnetosphere and connection of the geomagnetic to interplanetary field can be assisted by wind generated electric field in the ionosphere transferred by the good conductivity along the geomagnetic field to the magnetopause. This may account for some of the observed correlations between phenomena in the lower atmosphere and a component of magnetic disturbance.  相似文献   

10.
Laboratory experiments are described to simulate the solar wind flowing around nonmagnetic planets for three cases: non-conducting and ideally conducting planets, and a planet with a gaseous shell. A glass sphere was used as a model of a non-conducting planet (the Moon). Spatial distributions of plasma density and magnetic field strength that have been obtained agree with the data from measurements in space. However, the magnetic field does not increase before the rarefaction wave in the model experiment. A field increase was observed only for a conducting lunella: this argues in favour of the existence of a high conduction region on the Moon. A wax ball was used to model phenomena on the day-side of non-magnetic celestial bodies with a gaseoue shell (Venus, comets). Its surface easily evaporates in the plasma flow, and ionized evaporation products form an artificial ionosphere. The magnetic field frozen in the plasma flow is shown to be a determinative factor in the formation of a sharp ionospheric boundary. The supersonic plasma flow that interacts with the ionosphere gives rise to a stationary shock wave.  相似文献   

11.
This paper is concerned with the Kelvin-Helmholtz instability in the indissipative plasma with an external magnetic field. A detailed analysis is made of the results known from the approximation of a tangential discontinuity. The finiteness of the interface thickness effect is considered numerically at the arbitrary distribution of the density, velocity and magnetic field vectors inside this shear layer. The influence of plasma compressibility with an arbitrarily varying magnetic field is investigated. The main role of oblique disturbances with respect to the flow rate direction is shown under conditions of a large plasma compressibility. As such perturbations move away from the interface, their amplitude is damped much more slowly than in the case of weak compressibility. However, their wavelength remains, approximately, the same as that of longitudinal waves in the case of incompressibility. The linear approximation suggests the importance of oblique waves in the energetics of the interaction between the shear layer and the outward medium. A comparison is made of the instability period on discontinuities in the solar wind, and at magnetospheric and plasmaspheric boundaries, with the range of geomagnetic pulsations.  相似文献   

12.
Instabilities produced by finite-resistivity effects in a plasma are of great interest in connection with research in fusion devices, solar flares, and geomagnetic substorms. We elucidate here the physical mechanism of this instability, and in particular, identify the tendencies in the system towards the instability and the tendencies opposing it, if any. As an illustration, we consider the example of the so-called gravitational interchange mode wherein a plasma with a statically stable vertical density gradient is situated in a vertical gravitational field and a sheared horizontal magnetic field. The physical picture developed here may be useful in sorting out phenomena that appear when more subtle properties of the resistive modes in a plasma are considered.  相似文献   

13.
The time dependent one dimensional hydrodynamic equations describe the evolution of the thermal plasma flow along closed magnetic field lines outside of the plasmasphere. The convection of the supersonic polar wind onto a closed field line results in the assumed formation of collisionless plasma shocks. These shocks move earthward as the field line with its ‘frozen-in’ plasma remains fixed or contracts with time to smaller L coordinates. The high equatorial plasma temperature (of the order of electron volts) produced by the shock process decreases with time if the flow is isothermal but it will increase if the contraction is under adiabatic conditions. Assuming adiabaticity a peak in the temperature forms at the equator in conjunction with a depression in the ion density. After an initial contraction, if the flux tube drifts to higher L coordinates the direction of the shock motion can be reversed so that the supersonic region will expand along the field line towards the state characterizing the supersonic polar wind. A rapid expansion will lower the equatorial density while the temperature decreases with time under adiabatic but not isothermal conditions.  相似文献   

14.
The cold, core plasma mass density in the Earth's magnetosphere may be deduced from the resonant behaviour of ultra-low frequency (ULF; 1–100 mHz), magnetohydrodynamic (MHD) waves. Ground-based magnetometers are the most widely used instruments for recording the signature of ULF wave activity in the magnetosphere. For a suitable model of the background magnetic field and a functional form for the variation of the proton number density with radial distance, the resonant frequencies of ULF waves provide estimates of the equatorial plasma mass density. At high latitudes, the magnetic field model becomes critical when estimating the plasma mass density from FLR data. We show that a dipole field model is generally inadequate for latitudes greater than ∼65° geomagnetic compared with models that are keyed to magnetic activity, interplanetary magnetic field and solar wind properties. Furthermore, the method often relies on the detection of the fundamental ULF resonance, which changes frequency depending on the polarisation of the oscillation. Using idealised toroidal and poloidal oscillation modes, the range of the derived densities as the ULF wave polarisation changes is of the same order as changing the density function from a constant value throughout the magnetosphere to assuming constant Alfven speed in a dipole geometry.  相似文献   

15.
Hidalgo  M.A. 《Solar physics》2003,216(1-2):311-324
Using an elliptical cross-section model for the study of the magnetic topology of magnetic clouds (MCs) in the interplanetary medium, we develop an analytical approach to their relationship with geomagnetic storms. Assuming an axially symmetric ring current and once we have obtained the disturbances produced in its current density due to the passage of a MC through it (whose axis has a latitude θ, a longitude φ, and its cross-section has an orientation ζ), then we determine the decrease in the value of the geomagnetic field at the Earth's equator, i.e., the D st index. The D st model presented allows us to estimate the physical parameters which characterize the symmetric ring current during the recovery phase of the storm time. The theoretical and experimental D st indexes are compared for four intense geomagnetic storms (D st<−100 nT), all of them associated with MCs. As seen in the figures presented, the fits are good for every storm. In view of these results we conclude that the effects of a MC over the symmetric ring current can explain the main profile of the recovery phase of a geomagnetic storm.  相似文献   

16.
A finite-amplitude plane-polarised Alfvén wave is shown to undergo a modulational instability consequent to its trappping in density cavities which are created by the ponderomotive force associated with the Alfvén wave. The instability arises when the density cavity travels at subsonic speeds.  相似文献   

17.
Synoptic observations made on magnetic recording tape at Huancayo, Peru, at the magnetic dip equator, during the International Geophysical Year 1957–1958, were aurally reviewed at that time and no whistlers, hiss, or other emissions were heard. In view of the more recent observation of whistlers at geomagnetic latitudes as low as 12°, and in conjunction with a study of equatorial hiss observed in the topside ionosphere, these recordings have recently been reassessed by reducing them with modern real-time, digital spectrographic equipment. Although the observations were found to be of high quality, and to show the classical features of ground-wave and sky-wave propagation of sferics and VLF transmissions, again no evidence whatsoever of whistlers, hiss, or other emissions is found. Thus it is concluded that the whistlers observed at very low latitudes do not propagate subionospherically to the equator and it is confirmed that “hybrid” whistlers must be due to subionospheric propagation across the equator of the causative sferic rather than of the short whistler.  相似文献   

18.
A detailed analysis of rapid-run magnetograms from Guam (geomagnetic latitude = 4.2°) revealed that there are two kinds of geomagnetic sudden commencement (SC) observed in nighttime. One is the ordinary SC consisting of a main impulse only which has a smooth rise of the H-component. The other is a superposition by a small positive impulse on the very beginning part of the smooth rise of the main impulse and consequently the SC starts with a small stepwise increase of the H-component. The latter type of SC occurs between 20 and 08 h L.T. and its occurrence rate takes the maximum value of about 50% around 03 h L.T. Corresponding magnetograms from a dayside equatorial station (Huancayo, geomagnetic latitude = ?0.7°) were examined and a good correlation was found between the stepwise SC at the nightside (Guam) and SC1 with a preliminary reverse impulse (PRI) at the dayside (Huancayo). Since PRI observed at the dayside equator may be interpreted as an extension of an ionospheric current due to an dusk-to-dawn electric field impressed on the polar ionosphere, our results show that a polar originating ionospheric current can extend to the nightside equator and produce a small but observable magnetic effect in spite of much reduced nighttime ionospheric conductivity.  相似文献   

19.
Existing empirical models, e.g., the IRI and the PRIME model, have shortcomings for the upper-most F region and usually have no realistic formulation for the plasmasphere. These shortcomings can be overcome by replacing purely height oriented modeling by magnetic field aligned approaches.A magnetic field approximation is presented which uses dipole field lines with apexes above the dip equator. Modeling along these field lines can be based on diffusive equilibrium. For a single ion plasma (e.g., an H+ plasma) the integrations which are necessary to model along the field lines in a realistic way can be carried out by means of series expansions. For a multiple ion plasma and in case of arbitrary dependence of electron and ion temperatures on the coordinates one has to apply numerical integration.The principles of joining a field aligned model to a height oriented one are discussed including a method to cross the dip equator in a consistent way.A practical example is presented with a plasmasphere model added to the global model NeUoG which was developed at the University of Graz. The future development aims at replacing all of the topside F region of the model by a magnetic field aligned approach.  相似文献   

20.
Neutral density data were obtained near 400km (1600 LT) from a microphone density gauge on OGO-6 from 0°G to 40°N magnetic latitude for 25 September–3 October 1969. Several geomagnetic storms occurred during this period (ap varied from 0 to 207). Least-squares fits were made to data points on density-ap and density-Dst scatter diagrams, where the density values selected were delayed in time behind ap and Dst. An equation representing the least-squares fit was computed for each delay time. The equation of best fit (and the corresponding time delay between the density and the magnetic index which resulted in this best fit) was found by choosing the equation that gave the minimum standard error. For example, the best fit at 10°N geomagnetic latitude occurred for ap at t — 3 hr, where t is the time of the density values. The implications of the time differences associated with the best fits at various latitudes and longitudes are discussed with regard to the time delays involved in geomagnetic heating of the neutral upper atmosphere.

A low-latitude density bulge has been found between 0°N and 40°N whose magnitude varies with ap. DeVries (1972b) has independently discovered this daytime phenomenon. If the bulge is a semi-permanent feature near the equinoxes because of the enhanced geomagnetic activity, this may help explain the semi-annual effect in density, which was uncovered first in the drag data from low inclination satellites.  相似文献   


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