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1.
Solar type II radio bursts are interpreted as the radio signature of shock waves travelling through the solar corona. Some of these shock waves are able to enter into the interplanetary medium and are observed as interplanetary type II bursts. The nonthermal radio emission of these bursts indicates that electrons are accelerated up to superthermal and/or relativistic velocities at the corresponding shocks. Plasma wave measurements at interplanetary shock waves support the assumption that the fundamental type II radio emission is generated by wave-wave interactions of electron plasma waves and ion acoustic waves and that the source region is located near the transition region of the shock. Therefore, the instantaneous bandwidth of type II bursts should reflect the density jump across the shock. Comparing the theoretically predicted density jump of coronal shock waves (Rankine-Hugoniot relations) and the measured instantaneous bandwidth of solar type II radio bursts it is appropriate to assume that these bursts are generated by weak supercritical quasi-parallel shock waves. Two different mechanisms for the accelaration of electrons at this kind of shock waves are investigated in the form of test particle calculations in given magnetic and electric fields. These fields have been extracted from in-situ measurements at the quasi-parallel region at Earth’s bow shock, which showed large amplitude magnetic field fluctuations (so-called SLAMS: Short Large Amplitude Magnetic Field Structures) as constituent parts. The first mechanism treats these structures as strong magnetic mirrors, at which charged particles are reflected and accelerated. Thus, thermal electrons gain energy due to multiple reflections between two approaching SLAMS. The second mechanism shows that it is possible to accelerate electrons inside a single SLAMS due to a noncoplanar component of the magnetic field in these structures. Both mechanism are described in the form of test particle calculations, which are supplemented by calculations according to adiabatic theory. The results are discussed for circumstances in the solar corona and in interplanetary space. 相似文献
2.
V. V. Zaitsev E. Y. Zlotnik G. Mann H. Aurass A. Klassen 《Radiophysics and Quantum Electronics》1998,41(2):107-114
Herringbone bursts (HB-bursts) are the type III-like fine structure in type II bursts of solar radio emission and are usually
interpreted as plasma radiation arising from fast electrons accelerated by shock waves in the solar corona. In general outline,
the radiation mechanism of HB-bursts is similar to that of type III bursts. However, HB-bursts have brightness temperatures
that are about an order of magnitude higher than those of type III bursts. The frequency drift of BH-bursts is about two or
three times lower than that for type III bursts. All this shows that the fast-electron beams responsible for HB-bursts and
type III bursts differ markedly in their parameters. We calculated expected brightness temperatures of HB-bursts at the fundamental
and second harmonic and compared our results with Culgoora radiometer and radioheliograph data and Tremsdorf spectrograph
data in order to estimate parameters of fast-electron beams generating HB-bursts. We found that the observed brightness temperatures
of HB-bursts give velocities of fast electrons accelerated by shock waves within the limits (0.02–0.17)c. These velocities
are several times lower than those for type III bursts (0.15–0.5)c. The density of the fast electrons responsible for HB-bursts
is in the interval 3·10−6 <nb/n<6·10−5, which exceeds by 1–2 orders of magnitude the relative densities in type III sources. This gives a clue to understanding
the markedly higher brightness temperatures of HB-bursts compared to those of type III bursts. We concluded that the parameters
obtained for the agent exciting HB-bursts favor of turbulence mechanisms of electron acceleration by shock waves in the solar
corona.
Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia; Astrophysical Institute, Potsdam, Germany.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 2, pp. 164–176, February, 1998. 相似文献
3.
The first numerical simulations are presented for type-III solar radio bursts in the inhomogeneous solar corona and interplanetary space, that include microscale quasilinear and nonlinear processes, intermediate-scale driven ambient density fluctuations, and large scale evolution of electron beams, Langmuir and ion sound waves, and fundamental and harmonic electromagnetic emission. Bidirectional coronal emission is asymmetric between the upward and downward directions, and harmonic emission dominates fundamental emission. In interplanetary space, fundamental and/or harmonic emission can be important. Langmuir and ion sound waves are bursty and the statistics of Langmuir wave energy agree well with the predictions of stochastic growth theory. 相似文献
4.
The dispersion relation for ion sound waves generated in a perpendicular shock is derived and the energy density of ion-sound
turbulence is obtained using quasilinear theory. The result is compared with the lower hybrid turbulence generated under similar
conditions. It is shown that ion-sound turbulence is a better candidate for the generation of type-I radio bursts in the solar
corona. 相似文献
5.
Linear-mode conversion (LMC) of Langmuir waves to radiation near the plasma frequency at density gradients is important for space and astrophysical phenomena. We study LMC in warm magnetized plasmas using numerical electron fluid simulations when the density gradient is parallel to the ambient magnetic field (B0). We demonstrate that LMC can produce extraordinary- (x-) as well as ordinary- (o-) mode radiation from Langmuir waves, contrary to earlier expectations of o mode only. Equal amounts of o- and x-mode radiation are produced in the unmagnetized limit. The x-mode efficiency decreases as B0 increases, while the o-mode efficiency oscillates due to interference between incoming and reflected Langmuir waves. Both x and o modes should be produced for typical coronal and interplanetary parameters, alleviating the depolarization problem for type III solar radio bursts. 相似文献
6.
E. Ya. Zlotnik A. Klassen H. Aurass K. -L. Klein G. Mann 《Radiophysics and Quantum Electronics》1998,41(1):39-52
Spectrographic and partly imaging observations of three Type II solar radio bursts displaying three drifting bands with frequencies related as 1¬2¬3 are discussed. The radio data of two of these events were simultaneousely recorded by the digital radiospectrograph of the Observatory of Solar Radioastronomy in Potsdam-Tremsdorf and the radioheliograph of the Paris-Meudon Observatory in Nançay. The data allow the brightness temperatures of radio emission in the three frequency bands to be determined. The second harmonic is traditionally explained as a result of coalescence of two plasma waves into an electromagnetic wave at twice the plasma frequency. Two nonlinear merging processes—the coalescence of three plasma waves, and of a plasma wave and an electromagnetic wave at twice the plasma frequency—are considered to explain the occurrence of the third harmonic on Type II dynamic spectra. The analysis shows that both processes can fit the observed brightness temperatures of the second and third harmonic. The first process acts preferably at low phase velocities of plasma waves and sharp electron density gradients in the source, and the second process dominates in the case of high plasma wave phase velocities. It is shown that the occurrence of the third harmonic in type II bursts due to nonlinear processes in the coronal plasma indicates not only a powerful event but also some specific conditions in the shock or foreshock region. Finally, we propose a method to distinguish between the two invoked nonlinear processes by a statistical investigation of Type II burst data. 相似文献
7.
E. Ya. Zlotnik 《Radiophysics and Quantum Electronics》1994,37(7):533-542
Some ways of identifying magnetic fields in the solar corona using the observed properties of solar radio emissions are discussed. Examples are given for measuring the magnetic field in the active region atmosphere (in the chromosphere-corona transition region) based on spectral observations of microwave radiation from local sources associated with sunspots. Ways of determining the magnetic field in hot coronal loops in the case of recording cyclotron lines in solar microwave radiation are considered. It is shown that polarization of the second harmonic in Type III bursts testifies to a magnetic field on the track of electrons accelerated in the flare region and moving outward.Institute of Applied Physics, Russian Academy of Sciences, Nizhnii Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 7, pp. 821–835, July, 1994. 相似文献
8.
E. Ya. Zlotnik A. Klassen H. Aurass K. -L. Klein G. Mann 《Radiophysics and Quantum Electronics》1996,41(1):39-52
Spectrographic and partly imaging observations of three Type II solar radio bursts displaying three drifting bands with frequencies
related as 1?2?3 are discussed. The radio data of two of these events were simultaneousely recorded by the digital radiospectrograph
of the Observatory of Solar Radioastronomy in Potsdam-Tremsdorf and the radioheliograph of the Paris-Meudon Observatory in
Nan?ay. The data allow the brightness temperatures of radio emission in the three frequency bands to be determined.
The second harmonic is traditionally explained as a result of coalescence of two plasma waves into an electromagnetic wave
at twice the plasma frequency. Two nonlinear merging processes—the coalescence of three plasma waves, and of a plasma wave
and an electromagnetic wave at twice the plasma frequency—are considered to explain the occurrence of the third harmonic on
Type II dynamic spectra. The analysis shows that both processes can fit the observed brightness temperatures of the second
and third harmonic. The first process acts preferably at low phase velocities of plasma waves and sharp electron density gradients
in the source, and the second process dominates in the case of high plasma wave phase velocities. It is shown that the occurrence
of the third harmonic in type II bursts due to nonlinear processes in the coronal plasma indicates not only a powerful event
but also some specific conditions in the shock or foreshock region. Finally, we propose a method to distinguish between the
two invoked nonlinear processes by a statistical investigation of Type II burst data.
Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia; Astrophysical Institute, Potsdam, Germany;
Paris-Meudon Observatory, France. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 1, pp.
61–83, January, 1998. 相似文献
9.
PengFei Chen 《中国科学G辑(英文版)》2009,52(11):1785-1789
Magnetic field in the solar lower atmosphere can be measured by the use of the Zeeman and Hanle effects. By contrast, the
coronal magnetic field well above the solar surface, which directly controls various eruptive phenomena, can not be precisely
measured with the traditional techniques. Several attempts are being made to probe the coronal magnetic field, such as force-free
extrapolation based on the photospheric magnetograms, gyroresonance radio emissions, and coronal seismology based on MHD waves
in the corona. Compared to the waves trapped in the localized coronal loops, EIT waves are the only global-scale wave phenomenon,
and thus are the ideal tool for the coronal global seismology. In this paper, we review the observations and modelings of
EIT waves, and illustrate how they can be applied to probe the global magnetic field in the corona. 相似文献
10.
E. A. Zverev 《Radiophysics and Quantum Electronics》2006,49(9):657-668
The one-dimensional process of propagation of a spatially bounded electron stream in the solar corona is simulated. It is
shown that the background plasma inhomogeneity has a significant influence on the stream propagation and plasma-wave generation.
The results are qualitatively interpreted in application to type III solar radio bursts, and model dynamic spectra of such
bursts are constructed.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 9, pp. 731–743, September 2006. 相似文献
11.
Specific features of the double plasma resonance effect in a magnetized plasma of the solar corona are discussed. The effect
consists in enhanced generation of plasma waves in the regions where the upper hybrid frequency coincides with electron gyrofrequency
harmonics. It is widely used for interpretation of a fine structure in solar radio emission spectrum in the form of parallel
drifting quasi-harmonic stripes of enhanced radiation intensity (zebra pattern). It is shown that the plasma-wave growth rate
increases due to both dispersion properties of plasma waves, which are determined by the equilibrium plasma component, and
electrons which are non-equilibrium with respect to the velocities transverse to the magnetic field. Special attention is
given to an incorrect consideration of the double plasma resonance effect in some papers.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 2, pp. 95–108, February 2009. 相似文献
12.
Abranin É. P. Bazelyan L. L. Tsybko Ya. G. 《Radiophysics and Quantum Electronics》2000,43(12):923-937
We prove experimentally the possibility of direct observations of natural radio echoes on the Sun. The generally simple echo hypothesis on the origin of the time splitting in solar type IIId radio bursts sustained the crucial experimental test. These conclusions are based on both the new positional data and previous information obtained using the UTR-2 antenna system in different years since 1973.In summer 1992, we were able to register for the first time a large number of decameter type IIId bursts with pronounced echo-like components using a radioheliograph at frequencies of 20 and 25 MHz. Elementary (quasi-monochromatic) sources of the short-lived bimodal type IIId bursts were observed especially often on July 6. In this case, the time delay of the second peak, which depends on the heliolongitude of the active region, reached a maximum of about 7 s.All these double-peak bursts were localized in the central region of the solar corona, and, similar to the case of single-pulse limb type IIId bursts at a given radio frequency f, the observed elementary sources of these events appeared to be nonstationary. Such a dynamic pulsating source can radically change, at least once, its location in the celestial sphere in the field of view of a two-dimensional radio heliograph during the burst lifetime . While decaying, an echo-like burst formed rather slowly may abruptly jump from one location to another. As far as its short (3- to 4-s) steep-front precursor is concerned, its visible source behaved usually as an ephemeral sub- or ultrarelativistic object moving at a subluminal velocity over a global-scale trajectory.To all appearances, a twice-pulsing, narrow-band ( f/f 0.01) radio burst with an intensity-time profile of type IIId is generally a rather long-term ( 10-20 s) transient response of the solar atmosphere to the short-term flare of harmonic radio emission generated in the real (probably motionless and compact) source. This complex double-peak profile is due not only to the existence of a reflecting surface deep in the corona near the corresponding plasma level but also, to a considerable extent, to some opaque or semi-transparent structures located at heights of the middle corona. In particular, due to the strong influence of such structures, a coronal primary source of a bimodal burst can be seen on the Earth in some indirect rays before the solar radio echo and has the form of an additional delayed pulse. 相似文献
13.
Small-scale ion flux and magnetic field fluctuations in solar wind, foreshock and magnetosheath
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We have continued investigation of waves in the regions of
undisturbed solar wind, foreshock and magnetosheath. The analysis of
ion flux and magnetic field variations with the time interval 1--240s
was performed in the regions above. Very large variation in such a
time interval can be considered the common feature of the foreshock
and magnetosheath. The results of case and statistical studies showed
that the level of relative variations of ion flux and magnetic field
magnitude in foreshock is about 3 times larger than in undisturbed
solar wind. Variations of these parameters in the magnetosheath
topologically connected with the quasi-parallel bow shock are about
two times larger than those behind the quasi-perpendicular. We also
compared the results from Interball-1 data analysis with those from
statistical analysis of cluster magnetic field measurements. The
magnetic field variations obtained from the different satellite data
coincide with each other very well not only in quality but also in
quantity. 相似文献
14.
T. M. Mishonov M. V. Stoev Y. G. Maneva 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(3):533-536
Absorption of Alfvén waves is considered to be the main mechanism of
heating in the solar corona. It is concluded that the sharp increase
of the plasma temperature by two orders of magnitude is related to a
self-induced opacity with respect to Alfvén waves. The maximal
frequency for propagation of Alfvén waves is determined by the
strongly temperature dependent kinematic viscosity. In such a way
the temperature jump is due to absorption of high frequency Alfvén
waves in a narrow layer above the solar surface. It is calculated
the power per unit area dissipated in this layer due to damping of
Alfvén waves that blows up the plasma and gives birth to the
solar wind. A model short wave-length (WKB) evaluation takes into
account the 1/f2 frequency dependence of the transversal magnetic
field and velocity spectral densities. Such spectral densities agree
with old magnetometric data taken by Voyager 1 and recent
theoretical calculations in the framework of Langevin-Burgers MHD.
The presented theory predicts existence of intensive high frequency
MHD Alfvén waves in the cold layer beneath the corona. It is
briefly discussed how this statement can be checked experimentally.
It is demonstrated that the magnitude of the Alfvén waves
generating random noise and the solar wind velocity can be expressed
only in terms of satellite experimental data. It is advocated that
investigation of properties of the solar surface as a random driver by
optical methods is an important task for future solar physics. 相似文献
15.
Jun Lin 《中国科学G辑(英文版)》2009,52(11):1646-1654
Solar eruptions and the related processes involve magnetic fields and plasma flows of various scales in both time and space.
These processes include the convective motions of the mass and magnetic field in the photosphere, evolutions of magnetic fields
in both the chromosphere and the corona prior to and during the disruption of magnetic fields in response to the photospheric
motions. These evolutions constitute a whole process of transporting the magnetic energy and the helicity from the photosphere
to the corona, and then to interplanetary space. The present work, on the basis of a solar eruption model, discusses these
processes, and the related questions, unanswerable at present, but could be the scientific objectives of the space solar missions
in the future. 相似文献
16.
Ergun RE Malaspina DM Cairns IH Goldman MV Newman DL Robinson PA Eriksson S Bougeret JL Briand C Bale SD Cattell CA Kellogg PJ Kaiser ML 《Physical review letters》2008,101(5):051101
We show that observed spatial- and frequency-domain signatures of intense solar-wind Langmuir waves can be described as eigenmodes trapped in a parabolic density well. Measured solar-wind electric field spectra and waveforms are compared with 1D linear solutions and, in many cases, can be represented by 1-3 low-order eigenstates. To our knowledge, this report is the first observational confirmation of Langmuir eigenmodes in space. These results suggest that linear eigenmodes may be the starting point of the nonlinear evolution, critical for producing solar type II and type III radio bursts. 相似文献
17.
Small-scale ion flux and magnetic field fluctuations in solar wind, foreshock and magnetosheath
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We have continued investigation of waves in the regions of undisturbed solar wind, foreshock and magnetosheath. The analysis of ion flux and magnetic field variations with the time interval 1-240s was performed in the regions above. Very large variation in such a time interval can be considered the common feature of the foreshock and magnetosheath. The results of case and statistical studies showed that the level of relative variations of ion flux and magnetic field magnitude in foreshock is about 3 times larger than in undisturbed solar wind. Variations of these parameters in the magnetosheath topologically connected with the quasi-parallel bow shock are about two times larger than those behind the quasi-perpendicular. We also compared the results from Interball-1 data analysis with those from statistical analysis of cluster magnetic field measurements. The magnetic field variations obtained from the different satellite data coincide with each other very well not only in quality but also in quantity. 相似文献
18.
Coherent wave-wave coupling can produce radiation with a high efficiency. Recently, there has been a great deal of interest in the study of electro-magnetic wave generation in magnetized plasmas. We have investigated theoretically the effect of finite ion temperature on the parametric instability of an electro-static upperhybrid pump into an X-mode nonthermal radiation and low frequency ion waves in a two electron temperature plasma. The latter may include the lower-hybrid, the electron-acoustic and the ion-cyclotron waves. The loss cone distribution existing permanently at low altitudes acts as a free energy source generating the upper-hybrid waves. The upper-hybrid waves can also be present because of a linear instability produced by runaway electrons. Nonlinear dispersion relation and the growth rates are derived for each case using the hydrodynamical model. We find extra numerical factor arising due to the ions of finite temperature in the growth rate expression. This study may be useful in magnetosphere, auroral ionosphere, solar wind, solar radio bursts, and laboratory plasmas where ion has finite temperature and electrons have two distinct energy distributions. 相似文献
19.
S. A. Starodubtsev A. V. Grigor’ev V. G. Grigor’ev I. G. Usoskin K. Mursula 《Bulletin of the Russian Academy of Sciences: Physics》2007,71(7):991-993
The spectral characteristic of fluctuations of cosmic rays (CRs) and the interplanetary magnetic field in the prefront region of interplanetary shock waves, where coherent CR fluctuations with energies from ~10 keV to ~1 GeV are often observed, have been studied. It is concluded that the spectrum of CR fluctuations is subjected to modulation by fast magnetosonic waves generated by low-energy CRs reflected and/or accelerated at the shock fronts. 相似文献