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The dynamics of auroral arcs, observed in the prenoon sector during the 2-h period, has been studied in the context of ionospheric convection. The appearance of an isolated arc, the poleward drift velocity of which pronouncedly exceeded the plasma drift velocity, accompanied the IMF impulse and could result from the Alfvén resonance oscillations of the magnetosphere. Arcs that appeared after the northward turning of the IMF vertical component drifted poleward at a velocity close to the convection velocity. The mechanism of arc generation is related to the flute instability which develops in the region of the large-scale field-aligned current. Flute instability indications are found out in the POLAR satellite data. The study confirms the previously proposed classification criterion for dayside arcs with the source on closed field lines, based on the character of arc drift as compared to convection. 相似文献
3.
S. N. Ojha 《Pure and Applied Geophysics》1970,83(1):49-55
Summary By taking radiative parameters independent of magnetic field, the aim of this paper is to investigate the propagation of spherical shock in self-gravitating conducting gas spheres, such as stars, caused by an instantaneous central explosion of finite amount of energy. Ionisation, dissociation have not been taken into account and the medium is assumed to be a fully perfect gas. 相似文献
4.
A numerical model of the high-latitude ionosphere, which takes into account the convection of the ionospheric plasma, has been developed and utilized to simulate the F-layer response at auroral latitudes to high-power radio waves. The model produces the time variations of the electron density, positive ion velocity, and ion and electron temperature profiles within a magnetic field tube carried over an ionospheric heater by the convection electric field. The simulations have been performed for the point with the geographic coordinates of the ionospheric HF heating facility near Tromso, Norway, when it is located near the midnight magnetic meridian. The calculations have been made for equinox, at high-solar-activity, and low-geomagnetic-activity conditions. The results indicate that significant variations of the electron temperature, positive ion velocity, and electron density profiles can be produced by HF heating in the convecting high-latitude F layer. 相似文献
5.
《Journal of Atmospheric and Solar》2007,69(15):1884-1892
Plasma patches are regions of enhanced ionization that are created in the dayside cusp or equatorward of the cusp in the sunlit hemisphere during northward interplanetary magnetic field. After formation, and a change to a southward interplanetary magnetic field, they drift across the polar cap with the prevailing convection speed. As a plasma patch propagates, charge exchange reactions occur, which lead to the production of both ion and neutral particles throughout the patch. In the region directly above the patch, an upward jet of H+ and O+ forms. This ion jet, in turn, acts to produce an upward flux of neutral H and O stream particles because of charge exchange reactions between the ion jet and the background neutral atmosphere. A three-dimensional, time-dependent model of the ion and neutral polar winds was used in order to study the evolution of the neutral stream particles that are produced in a ‘representative’ propagating plasma patch, with the anticipation that the neutral stream particles produced by the ion jet would display a distinct signature. However, the outflow of neutral H atoms above a patch is only slightly visible in the simulation due to a continuous outflow flux of H (∼109 cm−2 s−1) across the entire polar cap. On the other hand, the upward flux of neutral O from the patch is more dependent on both the state of the ionosphere and the amount of heating, with increased upward fluxes over areas where the heating is high. Typically, the upward neutral O streams are predominantly located in the pre-midnight auroral oval. 相似文献
6.
The magnetopause separates the geomagnetic field from the interplanetary plasma and performs finite motions under the action
of the solar wind pressure variable in time. Accelerations originating in this case result in that the necessary condition
for the development of the Rayleigh-Taylor instability is formed at quite a definite motion phase. We can anticipate that
the instability will develop during compression of the magnetosphere. It should be taken into account that the magnetopause
is a potential tangential discontinuity. On the one hand, a plasma flow along the magnetopause results in a decrease in the
Rayleigh-Taylor instability threshold. On the other hand, the Kelvin-Helmholtz instability threshold, typical of the tangential
discontinuity, also decreases during the magnetosphere compression phase. Thus, if we speak about the magnetopause, it is
natural and necessary to jointly consider both types of instability. Main information on the combined Rayleigh-Taylor-Kelvin-Helmholtz
instability is presented, the dispersion equation determining the evolution of small perturbations is considered, and the
possible geophysical applications to the theory (e.g., penetration of the solar plasma into the magnetosphere, excitation
of global Pc5 oscillations) are indicated. 相似文献
7.
The theory of relaxation of geomagnetic depression observed during magnetic storm has been proposed based on the knowledge of the interaction between the Dst index and the magnetotail current. It has been indicated that the disruption of the tail current that was enhanced during the storm main phase can be caused by the interchange instability, which develops in the boundary plasma sheet due to the sheet curvature in the near to the Earth region and due to a sharp, directed toward the curvature center, plasma pressure gradient at the boundary between the plasma sheet and the tail lobe. The dispersion equation and expression for the instability growth rate have been obtained. The theoretically predicted characteristic time of storm depression relaxation τ is ～10 h and is in good agreement with the experimental estimate. 相似文献
8.
This study investigates the temporal evolution of the large plasma depletions observed by ROCSAT-1 and DMSP near 295°E during the 29–30 October 2003 storm. The presence of a penetration electric field around the detection time of the large plasma depletions is supported by the observation of high upward ion drift velocity and formation of an intense equatorial ionization anomaly in the American sector. However, these ionospheric disturbances occur in broad longitude regions; a short-range polarization electric field may adequately explain the creation of the large plasma depletions. The penetration electric field may trigger the Rayleigh–Taylor instability and produce abnormally large plasma depletions during the storm. The TIMED/GUVI and CHAMP observations provide an insight for the evolution of the large depletions several hours after their formation. The large depletions appear as arch-shaped emission depletions in the TIMED/GUVI image and as symmetric depletions paired in the magnetic north and south in the CHAMP observation. These characteristics can be explained by the “plasma depletion shell” phenomenon (Kil et al., 2009) produced by the westward shear flow of the ionosphere during the storm. 相似文献
9.
Ballooning disturbances in a finite-pressure plasma in a curvilinear magnetic field are described by the system of coupled equations for the Alfvén and slow magnetosonic modes. In contrast to most previous works that locally analyzed the stability of small-scale disturbances using the dispersion relationship, a global analysis outside a WKB approximation but within a simple cylindrical geometry, when magnetic field lines are circles with constant curvature, is performed in the present work. This model is relatively simple; nevertheless, it has the singularities necessary for the formation of the ballooning mode: field curvature and non-uniform thermal plasma pressure. If the disturbance finite radial extent is taken into account, the instability threshold increases as compared to a WKB approximation. The simplified model used in this work made it possible to consider the pattern of unstable disturbances at arbitrary values of the azimuthal wavenumber (k y ). Azimuthally large-scale disturbances can also be unstable, although the increment increases with decreasing azimuthal scale and reaches saturation when the scales are of the order of the pressure nonuniformity dimension. 相似文献
10.
Charged particle motion in magnetoactive plasma with an axially symmetric electrostatic field has been studied. It has been indicated that a difference between drift velocities of electrons and ions leads to a magnetic field disturbance. The equations for stationary magnetic field disturbances stretched along the magnetic field, which can be magnetic ducts for propagation of whistlers, have been obtained. The possibility of formation of such ducts by electrostatic fields from thunderstorm sources, penetrating into the ionosphere, has been estimated. 相似文献
11.
D. L. Pasmanik V. Y. Trakhtengerts A. G. Demekhov A. A. Lyubchich E. E. Titova T. Yahnina M. J. Rycroft J. Manninen T. Turunen 《Annales Geophysicae》1998,16(3):322-330
The formation of a zone of energetic electron precipitation by the plasmapause, a region of enhanced plasma density, following energetic particle injection during a magnetic storm, is analyzed. Such a region can also be formed by detached cold plasma clouds appearing in the outer magnetosphere by restructuring of the plasmasphere during a magnetic storm. As a mechanism of precipitation, wave-particle interactions by the cyclotron instability between whistler-mode waves and electrons are considered. In the framework of the self-consistent equations of quasi-linear plasma theory, the distribution function of trapped electrons and the electron precipitation pattern are found. The theoretical results are compared with experimental data obtained from NOAA satellites. 相似文献
12.
Using results of numerical modeling, the dynamics of escape of electrons, produced as a result beta-decay, to the external magnetic field from a spherical plasma volume with an expelled magnetic field is studied. The dependence of the fraction of escaped electrons on time and radius of the plasma volume has been obtained for two kinds of electron sources: a point isotropic source, located at the center of the sphere, and a volume isotropic source. It is shown that for a point source some part of electrons remains in the sphere, whereas for a volume source all electrons, at different values of the magnetic cavern radius, leave it at an identical relative escape rate. 相似文献
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The loss rate of fast electrons (with an energy much higher than the energy of the plasma electron thermal motion), when they
leave a magnetic cavern during a disturbance of the magnetic field azimuthal symmetry, is studied. The cases of point and
volume sources of fast particles have been considered. The plasma density in the cavern is supposed to be low, so that collisions
of fast electrons with plasma particles can be neglected. The effect of the electric field on particle motion is neglected
because it is assumed that the electric charge particles outgoing from the cavern is compensated by the counter current of
plasma conductivity electrons. The dependence of the loss value on the harmonic number and the amplitude of the cavern boundary
radius disturbance has been obtained. 相似文献
15.
The dynamics of the distribution of nonthermal electrons, injected into a collapsing magnetic trap, has been considered. The electron energy and pitch angle nonstationary spatial distributions in an extensive magnetic trap have been obtained for the first time for different laws of inhomogeneous magnetic field evolution in this trap by numerically solving the Fokker-Planck kinetic equation. The gyrosynchrotron emission intensity has been calculated for the obtained electron spatial distributions. It has been indicated that energetic electrons are effectively accumulated and accelerated at the top of a collapsing trap due to the first-order Fermi and betatron acceleration mechanisms at certain rates of variations in the magnetic field and background plasma density. 相似文献
16.
Abstract Magnetic field generation in a continuous medium in processes without self-excitation—the so-called semi-dynamo, involving as essential elements both magnetohydrodynamic processes and the presence of an impressed e.m.f.—has been studied for the case of the topological pumping effect on the magnetic field generation by an impressed e.m.f. operating in a three-dimensional Bénard convection layer. Under conditions of interest for astrophysical applications the magnetic flux produced can exceed substantially that excited by the e.m.f. in the absence of motion. The results obtained permitted an evaluation of the general quasi-steady magnetic field of the Sun generated by an azimuthal Coriolis e.m.f. which is active in the outermost layers of the convective envelope, taking into account small-scale convective and turbulent motions. In the polar regions of the Sun this field can reach ～10?1 G. 相似文献
17.
《Journal of Atmospheric and Solar》2004,66(11):987-995
An anisotropic kappa velocity distribution with loss-cones is used to investigate whistler wave instability occurring in the magnetosphere. The elements of the dielectric tensor and dispersion relation using modified plasma dispersion function with loss-cone angle have been obtained for the linear waves propagating exactly parallel to a uniform local magnetic field in a homogeneous and hot plasma. The modified plasma dispersion function and integrals have been expressed in power-series form for argument of ξ≫1. Temporal/spatial growth rates for whistler wave in the magnetosphere have been evaluated by the method of numerical techniques. The results of such a kappa loss-cone distribution function on the generation of whistler waves are compared with those obtained by Maxwellian loss-cone distribution. Calculations show that either a loss-cone or a thermal anisotropy in the hot plasma component of the magnetosphere can lead to the generation of incoherent emission of low-frequency whistler waves. This methodology could be easily extended to the study of low frequency emissions from planetary magnetospheres under suitable choice of models of density and magnetic field and other plasma parameters. 相似文献
18.
本文利用相对論带电粒子的两个寝渐不变量,討論了磁暴主相期間外輻射带中心結构的变化。作者认为磁暴主相是由“磁暴带”环电流所产生。“磁暴带”假設位于外輻射带中心之外,它是太阳等离子体穿入磁层后形成的。本文对初始能量W=20Kev和W=1Mev的电子分別进行了計算。 結果表明,在磁暴主相期間电子向外漂移,其赤道投擲角減小,但镜点离地面距离增高。因此,主相时所观測到的极光,并不是由于地磁場的平緩下降使小投擲角电子注入大气层而形成的。此外,計数率降低的主要原因是由于力管截面膨胀造成的粒子密度減小以及电子減速,而电子減速与投擲角有关,由此决定了电子通量沿磁力线分布的变化。以上結果与探险者6号（Explorer Ⅵ）的观測一致。 相似文献
19.
B. G. Verma 《Pure and Applied Geophysics》1970,83(1):21-30
Summary This paper considers a spherical shock, in a conducting gas, produced on account of explosion into an inhomogeneous self gravitating system. Similarity principles have been used to reduce the equations governing the flow to ordinary differential equations under the assumption that the density varies as an inverse-power of distance from the explosion centre. 相似文献
20.
P. N. Singh 《Pure and Applied Geophysics》1972,97(1):44-50
Summary The radial vibration in a composite cylindrical shell under the effect of a magnetic field has been investigated by solving the equations of elasticity, taking into account electromagnetic equations of Maxwell. The frequency equation has been obtained at the final stage. 相似文献