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1.
The one-dimensional process of spatially limited electron stream propagation in the solar corona is simulated. It is shown that the beam instability development results either in strong relaxation in velocity space and inhibition of spatial diffusion (high-stream density) or in velocity space relaxation decrease and simultaneous growth of spatial stream length (low-stream density). Assuming a profile of background plasma density to be exponential, dynamic spectra of type III bursts are modeled, which shows that the emission source velocity is constant, and a duration of the burst emission at a given frequency reduces for high-stream densities. 相似文献
2.
V. G. Ledenev 《Solar physics》2008,253(1-2):191-198
If plasma waves propagate in the direction of the plasma density decrease, their spectrum shifts to large wave numbers (to small phase velocities). This means that the spectrum of plasma waves excited by an electron beam concentrates near the distribution function (“plateau”) border, which shifts in the region of low velocities in the process of quasilinear relaxation. As the spectrum of excited plasma waves shifts in the region of large wave numbers, their frequency grows in accordance with the dispersion equation, which describes these waves. When the growth of the plasma wave frequency exceeds the decrease of the frequency owing to the regular inhomogeneity in the corona, the branch with positive frequency drift appears on the dynamic spectrum of the radio emission. Our computations allow us to estimate the density and energy of electron beams generating type U bursts. 相似文献
3.
Merits and demerits of recording of seismic signals at the bottom of water areas are considered. It is shown that long-term
seismological monitoring systems should be placed in the regions of industrial development of the shelf and continental slope
and in the areas of high seismic and tsunami hazard of oceans and seas. The results obtained during expeditions of the Shirshov
Institute of Oceanology of the Russian Academy of Sciences with the use of broadband bottom seismographs are reported. Autonomous
bottom seismographs with long-term operation at the bottom and operative communication via satellite and radio channels are
proposed for the formation of a marine seismological network. 相似文献
4.
This paper considers, in a linear approximation, the instability of a low-density electron beam propagating along the magnetic field of the solar corona, with respect to the excitation of electromagnetic (transverse) waves at cyclotron harmonics. It is shown that the extraordinary mode is excited at harmonics, beginning with the second and higher. Results of calculations check well with observed spectra of groups of solar spike radio bursts in the decimetric wavelength range. 相似文献
5.
Solar radio emission observations in the microwave frequency range show fine structures consisting of a number of almost parallel narrow-frequency bands. We interpret these bands as plasma emission at cyclotron harmonics. This emission is generated by the anisotropic electron beam, which excites longitudinal waves at a normal Doppler effect resonance. Subsequently, the longitudinal waves convert to radio emission at the second harmonic of the longitudinal wave frequency, and sometimes to the fundamental harmonic. The magnetic field strength is estimated on the basis of such a model in the microwave burst sources at 100–200 G. Estimates of the density variations are also made. 相似文献
6.
Agalakov B. V. Ledenev V. G. Lubyshev B. I. Nefedyev V. P. Yazev S. A. Zubkova G. N. Kerdraon A. Urbarz H. W. 《Solar physics》1997,173(2):305-318
Based on observations from the Siberian solar radio telescope, and invoking data from other observatories, we investigate preflare changes in the sunspot and floccular sources of radio emission and the development of an importance 2N flare in the chromosphere and corona in the active region on August 23, 1988.It has been ascertained that preflare changes became observable six hours prior to the flare onset and manifested themselves in intense flux fluctuations above the sunspot and in an enhancement of the source emission flux above the flocculus.It is shown that the flare onset is associated with a newly emerged magnetic flux in the form of a pore near the filament and with the appearance of radio sources above the filament. The flare was accompanied by type III radio bursts and a noise storm at meter wavelengths. Coronal mass ejection parameters are estimated from type III burst observations. 相似文献
7.
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
8.
The characteristics of low-damping high-frequency waves in hot magnetized solar and stellar coronal plasmas under the conditions
when the electron gyrofrequency ωHe is equal to or higher than the electron plasma frequency ωpe have been analyzed using the numerical solution of the dispersion equation. It is shown that the wave branches corresponding
to the Z mode and ordinary waves approach each other when the magnetic field increases and become almost indistinguishable in a wide
frequency range at all angles between the wave vector and magnetic field. A branch with anomalous dispersion appears at angles
close to 90°. A new interpretation of broadband pulsations and spikes is suggested on the basis of the results. 相似文献
9.
The characteristics of low-damping high-frequency waves in hot magnetized solar and stellar coronal plasmas under the conditions when the electron gyrofrequency ωHe is equal to or higher than the electron plasma frequency ωpe have been analyzed using the numerical solution of the dispersion equation. It is shown that the wave branches corresponding to the Z mode and ordinary waves approach each other when the magnetic field increases and become almost indistinguishable in a wide frequency range at all angles between the wave vector and magnetic field. A branch with anomalous dispersion appears at angles close to 90°. A new interpretation of broadband pulsations and spikes is suggested on the basis of the results. 相似文献
10.
A simple method of estimating the coronal magnetic field is suggested. It is based on the observational fact that the duration of the highly polarized part in type III bursts can be different, varying from a small fraction of the burst length to its total duration. We suggest that this difference is determined by the relation between the size of the region where only the ordinary wave can propagate and the size of the region where the burst is generated at a fixed frequency. The magnetic field is estimated at several tens of gauss in regions emitting highly polarized type III bursts at frequencies over 200 MHz. Density and magnetic field scales are estimated. 相似文献