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1.
本文在等离子体准线性理论下研究了地球同步轨道附近哨声湍流对亚暴“种子电子”的波-电子共振相互作用. 当发生这种共振时，“种子电子”的动量分布函数经动量扩散而随时间演化，部分低能电子数减少了，而高能尾部分的相对论电子（能量大于1MeV）数增加了，说明“种子电子”得到了哨声湍流的有效加速，且哨声湍流的能量越高，其加速效率越高. 另外，哨声湍流的频率越低（或波数越小），共振电子的能量越高（或单位质量的动量越大）；频率范围越宽，共振电子的能量范围越宽，被加速的电子数也越多. 磁层哨声湍流加速“种子电子” 大约在30h内就可以造成相对论电子数显著增加，这正好和大多数磁暴期间观测到的相对论电子通量的增长时间相当. 相似文献
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A. G. Demekhov V. Yu. Trakhtengerts M. J. Rycroft D. Nunn 《Geomagnetism and Aeronomy》2006,46(6):711-716
Acceleration of relativistic electrons in an inhomogeneous geomagnetic field during their resonant interaction with longitudinally propagating whistler-mode waves of varying frequency has been considered. Specific features of acceleration of electrons trapped by the wave field have been studied. Previous estimates of the efficiency of such acceleration have been generalized with regard to relativistic effects, and the simple formula for energy gain in a wide range of initial energies has been obtained. It has been indicated that the energy gain during a single interaction between electron and a whistler-mode wave packet, with typical parameters of an element of chorus emissions in the Earth’s magnetosphere, can reach several keV. The conditions of this acceleration mechanism realization are discussed. Specifically, it has been found that, in the case of chorus emissions in the Earth’s magnetosphere, this mechanism can be effective for electrons with perpendicular energies several times as high as such an energy of electrons generating chorus. 相似文献
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本文讨论了等离子体湍流对电子加速的两种模型:（1）假定在空间中存在一个空间均匀的等离子体湍流区,当具有一定初始分布的电子束通过此湍流区时,研究湍流场对电子束的加速过程;（2）在某一封闭的区域中,存在着具有一定初始分布和空间均匀的等离子体,当某种类型的等离子体波突然传入此等离子体区,然后考察此区中电子的加速过程。在这两种模型中,可能存在着某种电子消失机制。假定湍谱是幂指数形式,我们给出了不同类型湍流扩散系数的普遍形式。利用较简单的数学方法,求解了包括消失过程的一维准线性动力学方程,对于给定的初始分布,得出了分布函数的解析解,并给出了平均能量时间关系的表达式。另外,对于特定的湍谱指数,解出了当平行电场和湍流同时存在时的分布函数。最后,对所得结果进行了数值分析和讨论。 相似文献
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The dependence of the particle energy spectra on the acceleration and loss rates is studied based on the analytical solutions to the equation for the particle distribution function, taking into account diffusion in the momentum space (stochastic acceleration) and loss (due to particle escape from the acceleration region). The energy spectra and time dynamics of the MeV electron fluxes, observed based on the geostationary satellite data during the prolonged recovery phases of the known magnetic storms of June 11, 1980 and November 3–4, 1993, have been analytically described. The acceleration and loss rates have been estimated for these storms. A comparison is performed with the preciously studied energy spectra of MeV electrons and with the acceleration and loss rates during the recovery phases of the magnetic storms of January 10, 1997, and April 6, 2000. 相似文献
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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
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The energy spectrum of electrons with energies of 0.8–6.0 MeV has been analyzed based on the data of the Express-A2 geostationary
satellite and time variations in the fluxes of electrons with energies higher than 0.6 and 2 MeV (according to the GOES-10
satellite data) before and after a weak geomagnetic storm on April 9–10, 2002, which developed during the prolonged (about
ten days) recovery phase of a strong magnetic storm on April 6, 2000. The effect of the secondary injection and acceleration
caused by an intensification of substorm activity during a weak storm on the electron flux dynamics has been studied for the
first time. The energy spectra and time variations in the electron flux dynamics before and after a weak storm have been described
based on analytical solutions to the kinetic equation for the electron distribution function with regard to the stochastic
acceleration and loss rates. It has been established that there were different acceleration and loss rates before and after
the weak storm of April 9–10, 2000. 相似文献
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J. Torsti E. Valtonen L. Kocharov M. Lumme T. Eronen M. Louhola E. Riihonen G. Schultz M. Teittinen R. Vainio A. Anttila J. Kuusela 《Annales Geophysicae》1996,14(5):497-502
During solar flares and coronal mass ejections, nuclei and electrons accelerated to high energies are injected into interplanetary space. These accelerated particles can be detected at the SOHO satellite by the ERNE instrument. From the data produced by the instrument, it is possible to identify the particles and to calculate their energy and direction of propagation. Depending on variable coronal/interplanetary conditions, different kinds of effects on the energetic particle transport can be predicted. The problems of interest include, for example, the effects of particle properties (mass, charge, energy, and propagation direction) on the particle transport, the particle energy changes in the transport process, and the effects the energetic particles have on the solar-wind plasma. The evolution of the distribution function of the energetic particles can be measured with ERNE to a better accuracy than ever before. This gives us the opportunity to contribute significantly to the modeling of interplanetary transport and acceleration. Once the acceleration/transport bias has been removed, the acceleration-site abundance of elements and their isotopes can be studied in detail and compared with spectroscopic observations. 相似文献
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We derive the current-voltage relationship in the auroral region taking into account magnetospheric electrons for the bi-Maxwellian and kappa source plasma distribution functions. The current-voltage formulas have in principle been well known for a long time, but the kappa energy flux formulas have not appeared in the literature before. We give a unified treatment of the bi-Maxwellian and kappa distributions, correcting some errors in previous work. We give both exact results and two kinds of approximate formulas for the current density and the energy flux. The first approximation is almost generally valid and is practical to compute. The first approximation formulas are therefore suitable for use in simulations. In the second approximation we assume in addition that the thermal energy is small compared to the potential drop. This yields even simpler linear formulas which are suitable for many types of event studies and which have a more transparent physical interpretation than the first approximation formulas. We also show how it is possible to derive the first approximation formulas even for those distributions for which the exact results can not be computed analytically. The kappa field-aligned conductance value turns out always to be smaller than the corresponding Maxwellian conductance. We also verify that the obtained kappa current density and energy flux formulas go to Maxwellian results when k . 相似文献
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The direction and polarization degree of hard X rays (HXRs) in solar flares are studied. The continuous injection of relativistic electrons, which is implemented in powerful flares, is considered. The stationary relativistic kinetic equation is studied by using the method of expansion in terms of the Legendre polynomial and by integrating the equations for the expansion coefficients. The HXR characteristics are calculated using the bremsstrahlung relativistic cross-section for different angular and energetic electron distributions in the acceleration region. A high linear polarization degree of HXRs (??35%) has been obtained for narrow (??cos6??) beams of electrons with a soft spectrum (??E ?6); the polarization degree decreases with increasing quanta energy, whereas the directivity of a high-energy emission increases. This effect is absent for a nonrelativistic approximation. The considered model is applied to one of the most powerful flares in cycle 23, registered on October 28, 2003. The measured polarization degree values at relativistic energies (0.2?C0.4 and 0.4?C1 MeV) agree with the results achieved in the considered model when the electron energy spectrum index (?? = 2.5), angular distribution part (??cos6??), and the spectrum cutoff energy (E max = 1.3 MeV) were specified. 相似文献
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N. I. Izhovkina 《Geomagnetism and Aeronomy》2012,52(3):378-382
In the ARAKS experiment, electron pulses were injected into the ionosphere from onboard a rocket. For different series of pulses, the initial energy of electrons was 27 and 15 keV and the current strength was ∼0.5 A. On board the rocket, the distributions of electron fluxes directed toward the rocket were measured using the retarding potential by the electron energy up to 3000 eV. In this work, it is shown that the appearance of extreme values of the intensity of electron fluxes higher than 200 eV at the tail of the electron energy distribution can be explained by the nonmonotonic acceleration of electrons in the fields of electrostatic turbulence. The dynamics of electron and ion fluxes can be influenced by the polarization drift. It should be noted that extreme values of the flux intensities were not observed at heights lower than 130 km. This can be connected with the suppression of electrostatic oscillations by collisions of electrons with ionospheric components. 相似文献
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A statistical study of field-aligned electron beams associated with upflowing ion conics is presented from Exos-D (Akebono) observations below 10 000 km. The electron beams are narrowly collimated along the field line and generally have energies of several tens of eV. They are divided in the analysis into three types: upflowing, downflowing, and counterstreaming. All the types of electron beams are almost equivalent in their energy and pitch angle characteristics and their association rate with upflowing ion events. About 50% of ion conies are found to be coincident with field-aligned electron beams. There is also a correlation in energy between the field-aligned electrons and ion conics. These show that the association is not a mere coincidence but rather that the field-aligned acceleration of electrons is related to the perpendicular energization of ions. The association rate of upflowing electrons is high on the nightside, while that of downflowing electrons is high on the dayside. The association rate of downflowing electrons is high at low altitudes, and the rates of the three types of electron beams become equivalent at high altitudes. Data indicate that the height of the electron acceleration region is lower on the nightside. It is suggested that the average height of the electron acceleration region is around the satellite apogee (–10000 km), and the average thickness of the region is about thousands km. 相似文献
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《Journal of Atmospheric and Solar》2008,70(14):1829-1846
The observation that high speed solar wind streams are correlated with outer radiation belt electrons requires a transducer to convert this mechanical energy to hot electrons. We hypothesize that the high latitude cusp is the ideal location for this acceleration region. We support this hypothesis with two arguments: a forward model to show that the cusp can theoretically accelerate electrons to MeV energies which then are transported to the radiation belts; and, a backward model that deduces a cusp source based on empirical properties of the radiation belt MeV electrons. Accordingly, in the first half we apply the trapping properties of the static equinoctal cusp to deduce the dynamical response of interplanetary transients; in the second half we analyze several peculiar statistics of MeV electron correlations with solar wind as the response of a non-linear, multi-parameter dependence on the solar wind driver. Our model would permit the formulation of more physically accurate MeV electron predictors, which we demonstrate by connecting physical explanations to several empirical predictors recently published. 相似文献
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The general properties of the effect of the acceleration and loss rate on the time variations in relativistic electron fluxes have been studied based on the analytical solutions to the nonstationary equation for the particle distribution function, taking into account diffusion in the momentum space (stochastic acceleration) and loss (due to particle escape from the acceleration region). The results of calculating the time variations in the fluxes of electrons with energies of 1 MeV are presented for different ratios of the loss-to-acceleration rates. The cases of instantaneous and prolonged injection of low-energy particles are considered. It has been proposed to estimate the acceleration and loss rate effectiveness based on the observed electron flux decrease rate at the end of the magnetic storm recovery phase. 相似文献
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There are recent observational indications (lack of convergent electric field signatures above the auroral oval at 4 RE altitude) that the U-shaped potential drop model for auroral acceleration is not applicable in all cases. There is nevertheless much observational evidence favouring the U-shaped model at low altitudes, i.e., in the acceleration region and below. To resolve the puzzle we propose that there is a negative O-shaped potential well which is maintained by plasma waves pushing the electrons into the loss cone and up an electron potential energy hill at 3/4RE altitude range. We present a test particle simulation which shows that when the wave energization is modelled by random parallel boosts, introducing an O-shaped potential increases the precipitating energy flux because the electrons can stay in the resonant velocity range for a longer time if a downward electric field decelerates the electrons at the same time when waves accelerate them in the parallel direction. The lower part of the O-shaped potential well is essentially the same as in the U-shaped model. The electron energization comes from plasma waves in this model, but the final low-altitude fluxes are produced by electrostatic acceleration. Thus, the transfer of energy from waves to particles takes places in an energization region, which is above the acceleration region. In the energization region the static electric field points downward while in the acceleration region it points upward. The model is compatible with the large body of low-altitude observations supporting the U-shaped model while explaining the new observations of the lack of electric field at high altitude. 相似文献
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《Journal of Atmospheric and Solar》2008,70(7):980-990
In this paper, the propagation of two initially (z=0) parallel Gaussian electromagnetic beams, propagating in the z-direction in ionosphere, has been investigated. The nonlinearity in the dielectric function, responsible for the interaction between the beams arises from the redistribution of the electron density, caused by the nonuniform distribution of electron temperature determined by the Ohmic heating of the electrons and the energy loss of electrons on account of collisions. The wave frequencies have been assumed to be much larger than the electron collision frequency and gyrofrequency. A self-consistent solution of the electromagnetic wave equation and energy balance equation (considering the solar radiation) has been obtained in the paraxial approximation. Second-order coupled ordinary differential equations have been obtained for the distance between the centers of the beams and the beam widths in the x and y directions as a function of the distance of propagation along the z-axis. Using the available database for the mid-latitude daytime ionosphere, the equations have been solved numerically for a range of parameters and a discussion of the results has been presented. The physical basis for the fact that the beams move towards each other, when the resulting irradiance distribution of the two beams has a maximum in the space between the two beams, has been highlighted. 相似文献
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For electron acceleration during solar flares, it is very important to determine the pitch-angle and energy dependences of the electron distribution function. At present, this cannot be done directly from observations. Therefore, it is necessary to perform a numerical simulation of the propagation of accelerated electrons in the magnetic field of the flare loop (loops) and calculate the X-ray and radio emissions. For the solar flare of November 10, 2002, we have obtained qualitative and quantitative agreements of modeled X-ray and radio maps with the RHESSI satellite and Nobeyama Radioheliograph data. We have determined the flare model parameters that agree with observations. The pitch-angle anisotropy of electrons determined by highly directional functions of the S(α) = cos8(α) type, the energy spectrum consist of two electron populations, the low-energy part of the spectrum up to an energy of break of 350 keV is characterized by a power law with the exponent δ1 = 2.7–2.9, and the energy spectrum is more rigid above 420 keV (δ2 = 2–2.3). 相似文献