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1.
Fiber – or intermediate drift – bursts are a continuum fine structure in some complex solar radio events. We present the analysis of such bursts in the X17 flare on 28 Oct. 2003. Based on the whistler wave model of fiber bursts we derive the 3D magnetic field structures that carry the radio sources in different stages of the event and obtain insight into the energy release evolution in the main flare phase, the related paths of nonthermal particle propagation in the corona, and the involved magnetic field structures. Additionally, we test the whistler wave model of fiber bursts for the meter and the decimeter wave range. Radio spectral data (Astrophysikalisches Institut Potsdam, Astronomical Observatory Ond?ejov) show a continuum with fibers for ≈?6 min during the main flare phase. Radio imaging data (Nançay Radio Heliograph) yield source centroid positions of the fibers at three frequencies in the spectrometer band. We compare the radio positions with the potential coronal magnetic field extrapolated from SOHO/MDI data. Given the detected source site configuration and evolution, and the change of the fiber burst frequency range with time, we can also extract those coronal flux tubes where the high-frequency fiber bursts are situated even without decimeter imaging data. To this aim we use a kinetic simulation of whistler wave growth in sample flux tubes modeled by selected potential field lines and a barometric density model. The whistler wave model of fiber bursts accurately explains the observations on 28 Oct. 2003. A laterally extended system of low coronal loops is found to guide the whistler waves. It connects several neighboring active regions including the flaring AR 10486. For varying source sites the fiber bursts are emitted at the fundamental mode of the plasma frequency over the whole range (1200?–?300 MHz). The present event can be understood without assuming two different generation mechanisms for meter and decimeter wave fiber bursts. It gives new insight into particle acceleration and propagation in the low flare and post-CME corona. 相似文献
2.
The measurement of positions and sizes of radio sources in the observations of the fine structure of solar radio bursts is a determining factor for the selection of the radio emission mechanism. The identical parameters describing the radio sources for zebra structures（ZSs） and fiber bursts confirm there is a common mechanism for both structures. It is very important to measure the size of the source in the corona to determine if it is distributed along the height or if it is point-like. In both models of ZSs（the double plasma resonance（DPR） and the whistler model） the source must be distributed along the height, but by contrast to the stationary source in the DPR model, in the whistler model the source should be moving. Moreover, the direction of the space drift of the radio source must correlate with the frequency drift of stripes in the dynamic spectrum. Some models of ZSs require a local source, for example,the models based on the Bernstein modes, or on explosive instability. The selection of the radio emission mechanism for fast broadband pulsations with millisecond duration also depends on the parameters of their radio sources. 相似文献
3.
Gennady P.Chernov 《中国天文和天体物理学报》2010,10(9)
This review covers the most recent experimental results and theoretical research on zebra patterns(ZPs)in solar radio bursts.The basic attention is given to events with new peculiar elements of zebra patterns received over the last few years.All new properties are considered in light of both what was known earlier and new theoretical models.Large-scale ZPs consisting of small-scale fiber bursts could be explained by simultaneous inclusion of two mechanisms when whistler waves"highlight"the levels of double plasma resonance(DPR).A unique fine structure was observed in the event on 2006 December 13: spikes in absorption formed dark ZP stripes against the absorptive type Ⅲ-like bursts.The spikes in absorption can appear in accordance with well known mechanisms of absorptive bursts.The additional injection of fast particles filled the loss-cone(breaking the loss-cone distribution),and the generation of the continuum was quenched at these moments.The maximum absorptive effect occurs at the DPR levels.The parameters of millisecond spikes are determined by small dimensions of the particle beams and local scale heights in the radio source.Thus,the DPR model helps to understand several aspects of unusual elements of ZPs.However,the simultaneous existence of several tens of the DPR levels in the corona is impossible for any realistic profile of the plasma density and magnetic field.Three new theories of ZPs are examined.The formation of eigenmodes of transparency and opacity during the propagation of radio waves through regular coronal inhomogeneities is the most natural and promising mechanism.Two other models(nonlinear periodic space-charge waves and scattering of fast protons on ion-sound harmonics)could happen in large radio bursts. 相似文献
4.
A special fine structure (slowly drifting chains of narrowband fiber bursts), firstly observed during the solar type-IV radio burst on April 24, 1985, is interpreted as the radio signature of whistler waves periodically excited by a switch-on/switch-off process of a loss-cone instability in a localized wave packet of the fast magnetoacoustic mode. 相似文献
5.
Yu. F. Yurovsky 《Bulletin of the Crimean Astrophysical Observatory》2010,106(1):38-48
The multibeam propagation of radio waves in the solar plasma is analyzed, because the emission from a solar flare passes through
an inhomogeneous solar atmosphere on its way to the observer. A formula (a mathematical model) for calculating the structure
of the dynamic spectrum for flare radio bursts has been obtained. Comparison of the calculated spectra with the observed ones
shows that the results of interference explain the formation of a zebra structure and the separation of its stripes into individual
spikes, describe the time profile of the spikes, and explain the properties of fibers, ropes of fibers, and chains of “point”
bursts. The similarity of the dynamic spectra testifies that the fine structure of the spectra is formed not in the emission
source but as a result of the propagation of waves through the solar corona and interplanetary space. 相似文献
6.
A. A. Kuznetsov 《Solar physics》2006,237(1):153-171
The plasma mechanism of radio emission generation in an inhomogeneous medium is investigated. In the model under study, the
electron beam with loss-cone distribution generates upper-hybrid waves that, in turn, are transformed into radio emission.
It is shown that the influence of the plasma density inhomogeneity limits the plasma waves’ intensity considerably due to
variation in their wave vector. The results are used to interpret the intermediate drift (IMD) bursts. A model is proposed
in which these bursts are reflections of propagating small-scale (with amplitudes of about 1% and sizes of hundreds of kilometers)
magnetohydrodynamic (MHD) disturbances of magnetic tubes. It is shown that this model allows us to explain the spectral parameters
of the bursts in question. At present, the lack of precise and independent data about the magnetic field does not allow us
to decide definitively between the existing models (whistler or MHD waves) of the IMD bursts; nevertheless, if the proposed
model is correct, it can be used to determine the characteristics of the coronal MHD waves. 相似文献
7.
A dm-radio emission with fiber bursts observed on 11 July 2005 was analyzed using wavelet filtration and spectral methods.
In filtered radio spectra we found structures with different characteristic period P and frequency drift FD: i) fiber substructures (composed of dot emissions) with P
1≈ 0.5 s, FD1=− 87 MHz s−1 on average, ii) fiber structures with P
2≈1.9 s, and iii) drifting structures with P
3≈81.4 s, FD2=− 8.7, + 98.5, and − 21.8 MHz s−1. In the wavelet spectra we recognized patterns having the form of tadpoles. They were detected with the same characteristic
periods P as found for the filtered structures. The frequency drift of the tadpole heads is found to be equal to the frequency drift
of some groups of fibers for the long-period wavelet tadpoles (P
3) and to the frequency drift of individual fibers for the short-period tadpoles (P
2). Considering these wavelet tadpoles as signatures of propagating magnetoacoustic wave trains, the results indicate the presence
of several wave trains in the fibers’ source. While the long-period wave trains trigger or modulate a whole group of fibers,
the short-period ones look like being connected with individual fiber bursts. This result supports the model of fibers based
on magnetoacoustic waves. Using a density model of the solar atmosphere we derived the velocities of the magnetoacoustic waves,
107 and 562 km s−1, and setting them equal to the Alfvén ones we estimated the magnetic field in the source of fiber bursts as 10.7 and 47.8 G. 相似文献
8.
Wang Shujuan Yan Yihua Zhao Ruizhen Fu Qijun Tan Chengming Xu Long Wang Shijin Lin Huaan 《Solar physics》2001,204(1-2):153-164
25 MHz–7.6 GHz global and detailed (fine structure – FS) radio spectra are presented, which were observed in the NOAA 9077
active region for the Bastille Day (14 July 2000) flare at 10:10–11:00 UT. Besides broadband radio bursts, high-resolution
dynamic spectra reveal metric type II burst, decimetric type IV burst and various decimetric and microwave FSs, such as type III
bursts, type U bursts, reverse-slope (RS)-drifting burst, fiber bursts, patch and drifting pulsation structure (DPS). The
peak-flux-density spectrum of the radio bursts over the range 1.0–7.6 GHz globally appears as a U-shaped signature. Analyzing
the features of backbone and herringbones of the type II burst, the speeds of shock and relevant energetic electron beams
were estimated to be 1100 km s−1 and 58 500 km s−1, respectively. Also the time sequence of the radio emission is analyzed by comparing with the hard X-rays (HXRs) and the
soft X-rays (SXRs) in this flare. After the maxima of the X-rays, the radio emission in the range 1.0–7.6 GHz reached maxima
first at the higher frequency, then drifted to the lower frequency. This comparison suggested that the flare included three
successive processes: firstly the X-rays rose and reached maxima at 10:10–10:23 UT, accompanied by fine structures only in
the range 2.6–7.6 GHz; secondly the microwave radio emission reached maxima accompanied by many fine structures over the range
1.0–7.6 GHz at 10:23–10:34 UT; then a decimetric type IV burst and its associated FSs (fibers) in the range 1.0–2.0 GHz appeared
after 10:40 UT. 相似文献
9.
G. P. Chernov 《Solar physics》1990,130(1-2):75-82
This short report concerns a general consideration of whistler manifestations in fine structures, including possible trajectories of obliquely propagating whistlers, the role of quasilinear diffusion and an interpretation of new observations. A whistler ray tracing and kinetic whistler growth rates under arbitrary angles to the magnetic field in the solar corona were calculated. Different regimes of a whistler instability yield divers elements of fine structures: different stripes in emission and absorption or millisecond pulsations, moreover, zebra-stripes can convert into fiber bursts and inversely. A new explanation of low-frequency absorption in fibers is proposed: it is connected with an attenuation of plasma-wave instability due to the fast electron diffusion by whistlers. Rope-like chains of fiber bursts are explained by a periodic whistler instability in a magnetic reconnection region. 相似文献
10.
G. A. Dulk 《Solar physics》1990,130(1-2):139-150
The purpose of this paper is to review the observations of particle beams of the kind that are frequently observed in the interplanetary medium, usually but not always accompanying a solar flare. Most frequent are beams of electrons. They are generally associated with radio bursts of type III and only sometimes with flares and X-ray bursts. The properties of these electron beams have been well studied using quasi-linear and nonlinear theory, in situ observations of electrons and of plasma waves, and remote observations of radio waves Thanks to the interaction between theory and observation, the decade of the 1980s has been one of great progress in understanding the main features of these beams and their associated plasma waves and radio bursts. However, uncertainties remain in terms of (1) whether fine scale features, filamentary structures or wave condensations, occur together with the beams, (2) whether quasi-linear or nonlinear wave emission is the dominant process, and (3) if wave condensations are important, what is the mechanism of conversion of some Langmuir wave energy into radio emission.Other particle beams are composed of protons, of neutrons, of helium ions (sometimes with a large excess of 3He), and of heavy ions with varying concentrations. Sometimes the observations seem to require the fractionation of certain ions, followed by resonant acceleration of certain species.Objects other than the Sun that are the source of interplanetary particle beams include comets and planets, especially the Earth and Jupiter. 相似文献
11.
On April 21, 2002, a broadband solar radio burst was observed at about 01:00 – 03:00 UT with the digital spectrometers of
National Astronomical Observatories of China (NAOC). Also many fiber bursts superposed on the continuum bursts were detected
in the frequency range of 2.6 – 3.8 GHz during the time interval. After data processing, some parameters of the fibers such
as frequency drift rate, duration, bandwidth, and relative bandwidth were determined. The mean value of the frequency drift
was in the range of 42.3 – 87.4 MHz s−1 (negative). A theoretical interpretation for the fibers was presented based upon a model of the velocity of Alfvén solitons.
In this model, the source of the fiber emission was considered as the ducting of the solitons within the magnetic-mirror loop.
Then the magnetic field strength of the fiber source was estimated to be about 130 ≤ B0 ≤ 270 G. Also a comparison of the magnetic field estimation was made with another model of whistler group velocity. 相似文献
12.
To obtain constraints for models of fiber bursts, high-resolution time (0.01 s) profiles of the fiber bursts recorded at 1420 and 2695 MHz by the Trieste radiometers are studied in detail. The fiber bursts were identified using Ond?ejov radio spectra. During the years 2000?–?2005, 18 intervals with fiber bursts were selected; 26 groups were defined and about 700 fibers were analyzed in detail. More than 300 pulsations, present almost simultaneously with the fibers, were also selected and studied in order to find similarities or differences between these two types of fine structures. It was found that the polarization of the associated continuum, both for fiber bursts and pulsations, is practically the same. Evaluating the ratio between absorption over emission of many single fibers we found that this parameter is very different even for nearby bursts; however, we realized that this ratio shows a tendency to decrease with time. Finally, the time profile of one selected fiber burst was fitted using a recent model based on the modulation of the broadband radio emission by fast magnetoacoustic waves. The results are discussed. 相似文献
13.
A. N. Afanasiev 《Solar physics》2010,261(2):295-309
This paper investigates one of the kinds of fine structure of solar decametric type II radio bursts in the form of drifting
narrowband fibers. The appearance of such a structure is customarily explained by the features of the radio emission mechanism
in the source, which is formed when the shock wave catches up the previously-generated coronal mass ejection. On the other
hand, the characteristics of radio emission in the process of its propagation from the source to the observation point are
affected by inhomogeneities in the corona. Hence it is of considerable interest to estimate the role of the propagation effects
on the formation of fiber structures in radio bursts. Our calculations show that strong refraction effects (caustics) can
give rise to narrowband structures in the dynamic spectrum, resembling in their characteristics the fibers observed. 相似文献
14.
We report very high temporal and spectral resolution interferometric observations of some unusual solar radio bursts near
1420 MHz. These bursts were observed on 13 September 2005, 22 minutes after the peak of a GOES class X flare from the NOAA
region 10808. Our observations show 11 episodes of narrow-band intermittent emission within a span of ≈ 8 s. Each episode
shows a heavily frequency-modulated band of emission with a spectral slope of about −245.5 MHz s−1, comprising up to 8 individual blobs of emission and lasts for 10 – 15 ms. The blobs themselves have a spectral slope of
≈ 0 MHz s−1, are ≈ 200 – 250 kHz wide, appear every ≈ 400 kHz and last for ≈ 4 – 5 ms. These bursts show brightness temperatures in the
range 1012 K, which suggests a coherent emission mechanism. We believe these are the first high temporal and spectral resolution interferometric
observations of such rapid and narrow-bandwidth solar bursts close to 1420 MHz and present an analysis of their temporal and
spectral characteristics. 相似文献
15.
G. P. Chernov A. A. Stanislavsky A. A. Konovalenko E. P. Abranin V. V. Dorovsky G. O. Rucker 《Astronomy Letters》2007,33(3):192-202
We have performed a comparative analysis of the fine structure of two decametric type II bursts observed on July 17 and August 16, 2002, with the 1024-channel spectrograph of the UTR-2 radio telescope in the frequency range 18.5–29.5 MHz and with the IZMIRAN spectrograph in the frequency range 25–270 MHz. The August 16 burst was weak, ～2–5 s.f.u., but exhibited an unusual fine structure in the form of broadband fibers (Δf e > 250–500 kHz) that drifted at a rate characteristic of type II bursts and consisted of regular narrow-band fibers (Δf e > 50–90 kHz at 24 MHz) resembling a rope of fibers. The July 17 burst was three orders of magnitude more intense (up to 4500 s.f.u. at 20 MHz) and included a similar fiber structure. The narrow fibers were irregular and shorter in duration. They differed from an ordinary rope of fibers by the absence of absorption from the low-frequency edge and by slow frequency drift (slower than that of a type II burst). Both type II bursts were also observed in interplanetary space in the WIND/WAVES RAD2 spectra, but without any direct continuation. Analysis of the corresponding coronal mass ejections (CMEs) based on SOHO/LASCO C2 data has shown that the radio source of the type II burst detected on August 16 with UTR-2 was located between the narrow CME and the shock front trailing behind that was catching up with the CME. The July 17 type II fiber burst also occurred at the time when the shock front was catching up with the CME. Under such conditions, it would be natural to assume that the emission from large fibers is related to the passage of the shock front through narrow inhomogeneities in the CME tail. Resonant transition radiation may be the main radio emission mechanism. Both events are characterized by the possible generation of whistlers between the leading CME edge and the shock front. The whistlers excited at shock fronts manifest themselves only against the background of enhanced emission from large fibers (similar to the continuum modulation in type IV bursts). The reduction in whistler group velocity inside inhomogeneities to 760 km s?1 may be responsible for the unusually low drift rate of the narrow fibers. The magnetic field inside inhomogeneities determined from fiber parameters at 24 MHz is ～0.9 G, while the density should be increased by at least a factor of 2. 相似文献
16.
Close temporal correlation between high-frequency Langmuir waves and low-frequency electromagnetic whistler waves has been observed recently within magnetic holes of the solar wind. In order to account for these observations, a theory is formulated to describe the nonlinear coupling of Langmuir waves and whistler waves. It is shown that a Langmuir wave can interact nonlinearly with a whistler wave to produce either right-hand or left-hand circularly polarized electromagnetic waves. Nonlinear coupling of Langmuir waves and whistler waves may lead to the formation of modulated Langmuir wave packets as well as the generation of circularly polarized radio waves at the plasma frequency in the solar wind. Numerical examples of whistler frequency, nonlinear growth rate and modulation frequency for solar wind parameters are calculated. 相似文献
17.
V. N. Melnik A. A. Konovalenko H. O. Rucker V. V. Dorovskyy E. P. Abranin A. Lecacheux A. S. Lonskaya 《Solar physics》2010,264(1):103-117
Solar S-bursts observed by the radio telescope UTR-2 in the period 2001 – 2002 are studied. The bursts chosen for a detailed
analysis occurred in the periods 23 – 26 May 2001, 13 – 16 and 27 – 39 July 2002 during three solar radio storms. More than
800 S-bursts were registered in these days. Properties of S-bursts are studied in the frequency band 10 – 30 MHz. All bursts
were always observed against a background of other solar radio activity such as type III and IIIb bursts, type III-like bursts,
drift pairs and spikes. Moreover, S-bursts were observed during days when the active region was situated near the central
meridian. Characteristic durations of S-bursts were about 0.35 and 0.4 – 0.6 s for the May and July storms, respectively.
For the first time, we found that the instantaneous frequency width of S-bursts increased with frequency linearly. The dependence
of drift rates on frequency followed the McConnell dependence derived for higher frequencies. We propose a model of S-bursts
based on the assumption that these bursts are generated due to the confluence of Langmuir waves with fast magnetosonic waves,
whose phase and group velocities are equal. 相似文献
18.
Low frequency turbulence in the solar corona and fundamental radiation of type III solar radio burst
T. Takakura 《Solar physics》1979,62(2):375-382
On the basis of the previous numerical simulations, a new mechanism for the emission of the fundamental radio waves of solar radio type III bursts is presented. This hypothesis is to attribute the fundamental radio emission to the coalescence of the plasma waves with the low frequency turbulence, whistler or ion acoustic waves, pre-existing on the way of the electron beam which excite the plasma waves.It is estimated that ion acoustic waves could be occasionally unstable in the solar corona due to that drifting bi-Maxwellian distribution of electrons as observed in the solar wind, which is probably caused by collision-less heat conduction.It is also suggested that the reduced damping of the ion acoustic waves in such a distorted electron distribution in the corona may decrease the threshold electric current to cause the anomalous resistivity to be the onset of the solar flares. 相似文献
19.
Some 15% of solar flares having a soft X-ray flux above GOES class C5 are reported to lack coherent radio emission in the
100 – 4000 MHz range (type I – V and decimetric emissions). A detailed study of 29 such events reveals that 22 (76%) of them
occurred at a radial distance of more than 800″ from the disk center, indicating that radio waves from the limb may be completely
absorbed in some flares. The remaining seven events have statistically significant trends to be weak in GOES class and to
have a softer non-thermal X-ray spectrum. All of the non-limb flares that were radio-quiet above 100 MHz were accompanied
by metric type III emission below 100 MHz. Out of 201 hard X-ray flares, there was no flare except near the limb (R>800″) without coherent radio emission in the entire meter and decimeter range. We suggest that flares above GOES class C5
generally emit coherent radio waves when observed radially above the source. 相似文献
20.
We analyze a special kind of temporal fine structure in microwave radio emission for the 25 August 1999 solar flare observed
by the PMO spectrometer over the range of 4.5 – 7.5 GHz. This flare displays continuum emission after a group of reverse-slope
type III bursts around 6 GHz. High-resolution dynamic spectra reveal three evolving emission lines (EELs) following the type
III group. They are characterized by isolated, narrow, and continuous emission strips, which display frequency fluctuations
with time. Their frequency-drift rates are between −2 and 3 GHz s−1. Distinct from the EELs at lower frequencies, three EELs have a very short duration of a few seconds. They show an average
bandwidth of Δf≈330 MHz and a relative bandwidth of Δf/f≈0.057. This is the first time that this kind of fine structure has been observed around 6 GHz. 相似文献