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1.
A theoretical study is made of the whistler mode cyclotron instability both in linear and nonlinear regimes in conjunction with the generation of VLF emissions in the magnetosphere. For the nonlinear treatment, a well-established quasilinear method is used and some physical processes of the cyclotron instability viz. energy conservation, mechanism of instability and frequency change of the excited emissions are clarified. The results are applied to some types of the triggered VLF emissions; whistler triggered emissions and artificially stimulated emissions (ASE). It is found that whistler triggered emissions excited around the upper cutoff frequencies of whistlers may be explained by the whistler mode cyclotron instability by a model distribution function inferred from satellite data. In order to see a nonlinear evolution of the whistler mode cyclotron instability, computer simulations were carried out and it is shown that the change of frequency with time of whistler triggered emissions as well as characteristics of ASE are well explained by resonant nonlinear behaviour of whistler mode cyclotron instability considered in the present paper. 相似文献
2.
在中子星磁轴吸积柱的上部,少数高能电子通过磁镜点反射,可使部份电子的速度分布形成非热分布,由此激发激射(Maser)不稳定性。波被放大,发射出频率近似为电子迴旋频率及其倍频的相干辐射。用此模型计算了HerX-1的迴旋线发射。发现不稳定性增长率与吸积柱中电子数密度成正比,因而比非相干散射产生的连续辐射随电子数密度增长更快;而且发射线的强度和能量均与脉冲相位关联。这个理论可解释近期的HerX-1观测结果。 相似文献
3.
4.
The characteristics of VLF emissions during the two magnetic storms on 5–7 June and 19–21 September, 1967 are investigated based on the Ariel 3 satellite data and ground observation at a low-latitude station in Japan. During the study of the June event, the satellite lay in the dawn-dusk plane. Soon after the onset of the main phase there appeared VLF emissions on the morning side of the magnetosphere on the ground as well as on the satellite, but the emissions were at very low level in the evening. It was not until the recovery phase that we could recognize the stationary occurrence of intense emissions in the evening. Furthermore, it is found that the chorus-type morning emissions are observed outside the plasmapause, while the narrow-banded hiss-type evening emissions lay within the plasmapause. It is shown that the cyclotron instability of ring current electrons can, on the whole, account for the many properties of the storm-like emissions. Similarly, we discuss the characteristics of the September event. 相似文献
5.
黄光力 《紫金山天文台台刊》1999,18(3):343-349
利用北京天文台高时间和高频率分辨率的射电频谱仪对射电尖峰的测量,可以对背景等离子体参数进行的自洽诊断（ 磁场,密度,温度,波矢,及非热电子的性质） 。该诊断基于电子回旋脉塞不稳定性和回旋共振吸收。最后从诊断结果和太阳日冕典型参数的比较以确定尖峰辐射的谐波数。 相似文献
6.
Rising frequency VLF emissions having unusually high frequency and exhibiting banded structure were recorded between 14.55 and 15.30 U.T. on 28 June 1972 by the VLF goniometer receiver at Halley, Antarctica. The risers were split into two frequency groups, one with frequencies in the range 6.0–7.7 kHz and the other with frequencies between 7.8 and 9.4 kHz, the former being more numerous. The gap between the lower and upper frequency risers is superficially similar to, though at a higher frequency than, the missing bands in emissions observed by satellites. However, it is found to be unlikely that the risers received at Halley can be explained by any of the mechanisms advanced to explain the banded satellite-observed emissions. Several other explanations are considered and it is shown that the most likely is partial suppression by magnetospheric line radiation propagating in the same duct.The risers are interpreted as being generated via cyclotron resonance with counterstreaming electrons. A computer program based on Helliwell's (1967) phenomenological theory is used to determine the generation region and electron energies involved.Both frequency groups of risers display a 4 min periodicity in occurrence. It is shown that this time period is consistent with that required to replenish the flux of resonant electrons, by eastwards drift into the duct, after the emissions have been quenched due to the reduction of the flux by pitch-angle diffusion into the loss cone. 相似文献
7.
Using plasma parameters from a typical stormtime ionospheric energy balance model, we have investigated the effects of plasma turbulence on the auroral magnetoplasma. The turbulence is assumed to be comprised of electrostatic ion cyclotron waves. These waves have been driven to a nonthermal level by a geomagnetic field-aligned, current-driven instability. The evolution of this instability is shown to proceed in two stages and indicates an anomalous increase in field-aligned electrical resistivity and cross-field ion thermal conductivity as well as a decrease in electron thermal conductivity along the geomagnetic field. In addition, this turbulence heats ions perpendicular to the geomagnetic field and hence leads to a significant ion temperature anisotropy. 相似文献
8.
The purpose of the paper is to present the statistical characterictics of mid-latitude VLF emissions (both unstructured hiss and structured emissions) based on the VLF data obtained at Moshiri in Japan (geomag. lat. 35°; L = 1.6) during the period January 1974–March 1984. Local time dependence of occurrence rate and the association with geomagnetic disturbances have been studied for both types of emissions. Both types (unstructured and structured) of mid-latitude VLF emissions are found to have definite correlations with geomagnetic disturbances. Then, the time delay of the emission event behind the associated geomagnetic disturbance has enabled us to estimate the resonant electron energy for VLF hiss to be 5 keV at L = 3–4 and that for structured VLF emissions to be considerably larger, such as 20 keV at L 4. Combined considerations of these estimated resonant energies, theoretical electron drift orbits and the local time dependences, allow us to construct the following model to explain the experimental results in a reasonable way. Electrons in a wide energy range are injected during disturbances around the midnight sector, followed by the eastward drift. Lower energy ( 5 keV) electrons tend to drift closer to the Earth, resulting in the dawnside enhancement of VLF hiss within the plasmasphere. Further, these lower energy electrons are allowed to enter the duskside asymmetric plasmaspheric bulge and to generate VLF hiss there. On the other hand, higher energy (20 keV) electrons tend to drift at L shells farther away from the Earth and those substorm electrons are responsible for the generation of structured VLF emissions around dawn due to an increase of plasma density from the sunlit ionosphere. However, such higher energy electrons are forbidden from entering the duskside of the magnetosphere and so we cannot expect a duskside peak in the occurrence of structured VLF emissions, which is in agreement with the experimental result. 相似文献
9.
In the solar wind, electrostatic ion cyclotron waves can be excited, by electrons or ions when the flow velocity becomes supersonic. The instability of these waves is investigated for a situation in which ions are streaming in opposite directions along the interplanetary magnetic field in a uniform background of relatively stationary electrons. Many modes become unstable under the existing conditions. It is conjectured that the excitation of this instability may lead to a steady state electrostatic turbulence in the solar wind. 相似文献
10.
Fernando M. Serra 《Planetary and Space Science》1984,32(8):985-1005
The mutual influence between two whistler mode waves, through cyclotron resonant interaction of each wave with the same set of energetic electrons, is analysed both theoretically and by computer simulations ; this two-wave interaction mechanism seems to be an important process in understanding recently observed phenomena in Siple Station VLF multi-wave injection experiments. A criterion is established to estimate the threshold for the critical frequency spacing (for given wave amplitudes) for a significant mutual interaction between two monochromatic waves to occur. This criterion is based on the overlap of coherence bandwidths associated with the trapping domains of each wave and it takes into account the geomagnetospheric medium inhomogeneity. The effects of a perturbing second wave on electrons trapped by a first wave is discussed, considering the general situation of varying-frequency waves, and a simulation model is used to track the motion of test-electrons in the two-waves field. Conditions leading to detrapping and subsequent trapping by the second wave of previously first-wave trapped electrons are analysed and suggest the possibility of this phenomenon to play an important role in frequency entrainment and energy exchange between two waves. 相似文献
11.
Dean F. Smith 《Solar physics》1980,66(1):135-148
Requirements for the number of nonthermal electrons which must be accelerated in the impulsive phase of a flare are reviewed. These are uncertain by two orders of magnitude depending on whether hard X-rays above 25 keV are produced primarily by hot thermal electrons which contain a small fraction of the flare energy or by nonthermal streaming electrons which contain > 50% of the flare energy. Possible acceleration mechanisms are considered to see to what extent either X-ray production scenario can be considered viable. Direct electric field acceleration is shown to involve significant heating. In addition, candidate primary energy release mechanisms to convert stored magnetic energy into flare energy, steady reconnection and the tearing mode instability, transfer at least half of the stored energy into heat and most of the remaining energy to ions. Acceleration by electron plasma waves requires that the waves be driven to large amplitude by electrons with large streaming velocities or by anisotropic ion-acoustic waves which also require streaming electrons for their production. These in turn can only come from direct electric field acceleration since it is shown that ion-acoustic waves excited by the primary current cannot amplify electron plasma waves. Thus, wave acceleration is subject to the same limitations as direct electric field acceleration. It is concluded that at most 0.1% of the flare energy can be deposited into nonthermal streaming electrons with the energy conversion mechanisms as they have been proposed and known acceleration mechanisms. Thus, hard X-ray production above 10 keV primarily by hot thermal electrons is the only choice compatible with models for the primary energy release as they presently exist. 相似文献
12.
The resonant interaction between the whistler mode waves and the energetic electrons near the plasmapause boundary has been studied in the presence of field aligned currents which seem to exist during substorm activity. It is shown that the electrons which carry the current along the direction of the magnetic field enhance the whistler mode growth considerably if the streaming velocity is small compared to the phase velocity of the wave. It is likely that this is one of the mechanisms explaining the intense VLF emissions observed near the plasmapause during substorm activity. 相似文献
13.
Employing a realistic ionospheric model and a suitable energetic electron spectra, detailed power calculations are carried out to confirm the generation mechanism of low-latitude VLF emissions observed both in the satellites and on the ground. Raypaths of the radiated waves are also calculated to account for the attenuation and spreading losses. It is shown that 100 eV?1 keV electrons radiating incoherently in the Cerenkov mode are the main sources of these emissions. 相似文献
14.
S. K. El-Labany R. Sabry W. M. Moslem E. A. Elghmaz 《Astrophysics and Space Science》2014,349(2):773-780
Generation of quasielastic electron-acoustic (EA) waves head-on collision are investigated in non-planar (cylindrical/spherical) plasma composed of cold electrons fluid, hot electrons obeying nonthermal distribution, and stationary ions. The cylindrical/spherical Korteweg-de Vries (KdV) equations describing two bidirectional EA waves are derived and solved analytically. Numerical investigation have shown that only positive electron-acoustic (EA) structures can propagate and collide. The analytical phase shift |Δ A | due to the non-Maxwellian (nonthermal) electrons is different from the Maxwellian case. Both the hot-to-cold electron number density ratio α and nonthermal parameter β have opposite effect on the phase shift behavior. The phase shift of the spherical EA waves is smaller than the cylindrical case, which indicates that the former is more stable for collision. The relevance of the present study to EA waves propagating in the Earth’s auroral zone is highlighted. 相似文献
15.
Experimental data describing the effect of the South Atlantic anomaly on E? 280 keV electron flux at L = 2 and high B values, are compared to the numerical solution of a pitch-angle diffusion equation with a varying loss cone. The diffusion coefficient needed to explain replenishment of the electrons lost over the anomaly is found to be 3.2 × 10?2 sec?1 Calculation of the diffusion coefficient due to cyclotron resonant interaction with VLF electro-magnetic waves leads to the conclusion that the observed wave spectral density can yield the needed diffusion coefficient. 相似文献
16.
Jian－ChengWang 《中国天文和天体物理学报》2002,2(1):1-7
1 INTRoDUCTIONB1azars are rwho-loud AGNs characterized by emissions of strong and raPidiy wriablenOllthermal radiation over the elltire electromagntic spectrum. Syndritron ehasha followedby inverse ComPton scattering in a re1aivistic jet and beamd inio one directiOn is generallythought to be the IneCha8m powering these Objects (Kollgaard 1994; Urry & Paded 1995).All blazars have a sPectral energy distribution (SED) with tWO peak8 in a uFv rePesentation(von Montigny et al. 1995; S… 相似文献
17.
N. R. Kundu M. M. Masud K. S. Ashrafi A. A. Mamun 《Astrophysics and Space Science》2013,343(1):279-287
A rigorous theoretical investigation has been made on multi-dimensional instability of obliquely propagating electrostatic dust-ion-acoustic (DIA) solitary structures in a magnetized dusty electronegative plasma which consists of Boltzmann electrons, nonthermal negative ions, cold mobile positive ions, and arbitrarily charged stationary dust. The Zakharov-Kuznetsov (ZK) equation is derived by the reductive perturbation method, and its solitary wave solution is analyzed for the study of the DIA solitary structures, which are found to exist in such a dusty plasma. The multi-dimensional instability of these solitary structures is also studied by the small-k (long wave-length plane wave) perturbation expansion technique. The combined effects of the external magnetic field, obliqueness, and nonthermal distribution of negative ions, which are found to significantly modify the basic properties of small but finite-amplitude DIA solitary waves, are examined. The external magnetic field and the propagation directions of both the nonlinear waves and their perturbation modes are found to play a very important role in changing the instability criterion and the growth rate of the unstable DIA solitary waves. The basic features (viz. speed, amplitude, width, instability, etc.) and the underlying physics of the DIA solitary waves, which are relevant to many astrophysical situations (especially, auroral plasma, Saturn’s E-ring and F-ring, Halley’s comet, etc.) and laboratory dusty plasma situations, are briefly discussed. 相似文献
18.
It is shown that the existing theory of type II bursts, based on a model of the emission from the shock wave front, has difficulties when compared with observational data. We suggests a new model for type II bursts. According to this model, in an expanding magnetic loop a cluster of energetic electrons acts to excite the cyclotron instability of plasma waves. The waves are excited on surfaces where the cyclotron resonance condition is satisfied, and are then transformed into electromagnetic emission by merging. Our proposed model may be useful to explain some observational facts, such as the narrow-band character of the emission and the space-time relationship between the harmonics. Some tests to check the validity are proposed. 相似文献
19.
A. K. Tripathi R. P. Singhal K. P. Singh O. N. Singh II 《Astrophysics and Space Science》2014,352(2):421-427
Jupiter’s moon—Ganymede—is the largest satellite in our solar system. Galileo spacecraft made six close flybys to explore Ganymede. More information was acquired about particle population, magnetic field and plasma waves during these encounters. In this paper, our aim is to study the generation of electrostatic electron cyclotron harmonic (ECH) emissions in the vicinity of Ganymede using the observed particle data. The calculated ECH wave’s growth rates are analyzed in the light of observations of plasma waves along the path of Galileo near Ganymede. Dispersion relation for electrostatic mode is solved to obtain the temporal growth rates. A new electron distribution function, fitted to distribution observed near Ganymede, is used in the calculations. A parametric study is performed to evaluate the effect of loss-cone angle and the ratio of plasma to gyro-frequency on growth rates. It is found that ECH waves growth rates generally decrease as the loss-cone angle is increased. However, the ratio plasma to gyro-frequency has almost no effect on the growth rates. These parameters vary considerably along the Galileo trajectory near Ganymede. This is the first study which relates the occurrence of ECH waves with the particle and magnetic field data in the vicinity of Ganymede. The study of ECH wave growth rate near Ganymede is important for the calculation of pitch angle scattering rates of low-energy electrons and their subsequent precipitation into the thin atmosphere of Ganymede producing ultraviolet emissions. Results of the present study may also be relevant for the upcoming JUNO and JUICE missions to Jupiter. 相似文献
20.
S. K. Zaghbeer H. H. Salah N. H. Sheta E. K. El-Shewy A. Elgarayh 《Astrophysics and Space Science》2014,353(2):493-500
Propagation of nonlinear dust-acoustic waves in a magnetized collisionless plasma having positively, negatively charged dust grains and nonextensive distributed electrons and ions has been investigated. A reductive perturbation method is used to obtain a nonlinear Korteweg-de Vries (KdV) equation describing the model. The dynamics of the modulational instability gives rise to the formation of rogue waves that is described by a nonlinear Schrödinger equation. The dependence of rogue waves profiles on positive and negative charged dust cyclotron frequencies, nonextensive parameters of electrons and ions is investigated numerically. The result of the present investigation may be applicable to some plasma environments, such as cometary tails and upper mesosphere. 相似文献