Unusual Solar Radio Burst Observed at Decameter Wavelengths

An unusual solar burst was observed simultaneously by two decameter radio telescopes UTR-2 (Kharkov, Ukraine) and URAN-2 (Poltava, Ukraine) on 3 June 2011 in the frequency range of 16?–?28 MHz. The observed radio burst had some unusual properties, which are not typical for the other types of solar radio bursts. Its frequency drift rate was positive (about 500 kHz?s^?1) at frequencies higher than 22 MHz and negative (100 kHz?s^?1) at lower frequencies. The full duration of this event varied from 50 s up to 80 s, depending on the frequency. The maximum radio flux of the unusual burst reached ≈10³ s.f.u. and its polarization did not exceed 10 %. This burst had a fine frequency-time structure of unusual appearance. It consisted of stripes with the frequency bandwidth 300?–?400 kHz. We consider that several accompanied radio and optical events observed by SOHO and STEREO spacecraft were possibly associated with the reported radio burst. A model that may interpret the observed unusual solar radio burst is proposed.     

Solar Drift Pair Bursts in the Decameter Range

The results of observations of solar decametric drift pair bursts are presented. These observations were carried out during a Type III burst storm on July 11–21, 2002, with the decameter radio telescope UTR-2, equipped with new back-end facilities. High time and frequency resolution of the back-end allowed us to obtain new information about the structure and properties of these bursts. The statistical analysis of more than 700 bursts observed on 13–15 July was performed separately for “forward” and “reverse” drift pair bursts. Such an extensive amount of these kind of bursts has never been processed before. It should be pointed out that “forward” and “reverse” drift pair bursts have a set of similar parameters, such as time delay between the burst elements, duration of an element, and instant bandwidth of an element. Nevertheless some of their parameters are different. So, the absolute average value of frequency drift rate for “forward” bursts is 0.8 MHz s⁻¹, while for “reverse” ones it is 2 MHz s⁻¹. The obtained functional dependencies “drift rate vs. frequency” and “flux density vs. frequency” were found to be different from the current knowledge. We also report about the observation of unusual variants of drift pairs, in particular, of “hook” bursts and bursts with fine time and frequency structure. A possible mechanism of drift pairs generation is proposed, according to which this emission may originate from the interaction of Langmuir waves with the magnetosonic waves having equal phase and group velocities.     

Harmonics of Solar Radio Spikes at Metric Wavelengths

This paper presents the latest observations from the newly built solar radio spectrograph at the Chashan Solar Observatory. On July 18, 2016, the spectrograph records a solar spike burst event, which has several episodes showing harmonic structures, with the second, third, and fourth harmonics. The lower harmonic radio spike emissions are observed later than the higher harmonic bands, and the temporal delay of the second (third) harmonic relative to the fourth harmonic is about 30?–?40 (10) ms. Based on the electron cyclotron maser emission mechanism, we analyze possible causes of the temporal delay and further infer relevant coronal parameters, such as the magnetic field strength and the electron density at the radio source.     

Scintillation of Solar Radio Sources: Implication for Spikes

Possible scattering regimes of the emission from a solar radio source due to dielectric permitivity fluctuations of an extended coronal plasma co-rotating with the Sun are discussed. The exact and approximate expressions are given for the spectrum of temporal intensity fluctuations in the regime of weak scattering. The frequency, at which the spectrum shows a bend, is determined by the location of the effective scattering screen if the source size is not too large. In the regime of strong scattering of the emission from a broadbanded nonimpulsive radio source, the formation of random intensity spikes, namely millisecond, narrowbanded spike bursts is a possibility. Their apparent size can be quite significant. However, the sources with very small true sizes are required in order to produce strong spikes.     

Mathematical Modeling of the Formation of Type IIId Solar Decameter Radio Bursts with Echo Components

Using numerical simulation, we investigate the possibility that echo components of type IIId solar decameter bursts can be produced through refraction of radio emission in a coronal plasma with large-scale regular electron density inhomogeneities. It is shown that the observed time profiles of radio burst intensity with three or four maxima can be related to the presence in the middle corona of streamers and a localized regular nonuniformity whose electron density exceeds background electron density by a factor of more than 3 – 4. The nonuniformity scale in this case is comparable with the optical diameter of the solar disk. The observed radio burst echo components with delays longer than 3 s are explained by the production of additional radio emission propagation modes within a “transverse" refraction waveguide arising between the localized electron density nonuniformity and deeper layers in the corona. As these additional modes are reflected from the streamers, they can reach the Earth. Calculations of the time profile of radio burst intensity take into consideration the influence of scattering by turbulent coronal inhomogeneities and of collisional absorption. Comparison of the modeling results with the observational data shows that the calculated values of some profile parameters differ from the observed values. One of the possible reasons is that the method used does not take into account the diffraction leakage of radio emission through the large-scale nonuniformity.     

太阳分米波尖峰辐射最小带宽的探讨

云南天文台0.6～1.5GHz太阳射电快速动态频谱仪,在2001年6月24日的射电爆发中观测到大量尖峰。由于观测仪器有相当高的频率分辨率,使我们可以对尖峰的绝对带宽进行更精细的统计分析。由于尖峰数量很大,特别编制了识别尖峰并测量其带宽的软件来进行统计工作。结果发现76%的尖峰的绝对带宽达到仪器频率分辨率1.4MHz,其相对带宽达到0.1%。这比以前关于尖峰辐射带宽的统计结果要小很多。统计结果支持用ECM机制解释尖峰辐射。     

Decameter Type III-Like Bursts

We report the first observations of Type III-like bursts at frequencies 10 – 30 MHz. More than 1000 such bursts during 2002 – 2004 have been analyzed. The frequency drift of these bursts is several times that of decameter Type III bursts. A typical duration of the Type III-like bursts is 1 – 2 s. These bursts are mainly observed when the source active region is located within a few days from the central meridian. The drift rate of the Type III-like bursts can take a large value by considering the velocity of Type III electrons and the group velocity of generated electromagnetic waves.     

Decameter storm radiation,II

The physical properties of six decametric storms, observed at Clark Lake Radio Observatory are studied. The height of the storm continuum sources was determined from the rotation rate. Assuming that the radiation originates at the plasma frequency we computed the gradient of electron density for the regions where the storms originate. The mean angular size of the decametric continuum sources is large; it increases with decreasing frequency. The storm continuum is found to be strongly directive toward the disk center. The east-west asymmetry, well observed at meter wavelengths is also observed at decameter wavelengths. The occurrence of two distinct classes of type III bursts in storms is discussed: ‘off-fringe’ and ‘onfringe’ type Ill's. The ‘off-fringe’ Ill's are found to be displaced in position from the continuum source ; on the other hand, the ‘on-fringe’ ones coincide in position with the continuum. These two kinds of bursts differ in other properties as well. A model of the storm region is proposed. The continuum radiation and the ‘on-fringe’ type III's are believed to originate above closed magnetic loops, in regions of diverging field lines; the ‘offfringe’ type Ill's are thought to be excited by energetic electron streams, having access to open magnetic field lines at the base of the loops.     

Decameter storm radiation,I

A log-periodic array, 3 km long in the E-W direction is in operation at the Clark Lake Radio Observatory. The solar brightness distribution is swept once per second in the 65-20 MHz frequency range. The analysis of the interferometer records allows the determination of one dimensional solar burst positions, to an accuracy of 0.1 R at 60 MHz and 0.3 R at 30 MHz, approximately.Six long duration noise storms have been observed over an eight month period, extending from January to September, 1971. The storms are described and their relation to chromospheric active regions and flares is discussed. Decametric storms are found to be related to complexes of interacting active regions. The interaction is studied in terms of the number of simultaneous flares observed to occur in the various active regions. On the average, twice as many simultaneous flares are observed than would be expected if flares occurred at random. An analysis of coronal magnetic field maps computed from longitudinal photospheric fields shows magnetic arcades and some divergent field lines at the site of storm regions. Decimeter and meter wavelength sources are found to be associated with all decameter storms. At decimeter wavelengths double or multiple sources are often seen above individual active regions forming part of the chromospheric complex.     

Decameter type IV bursts associated with coronal transients

Recent observations of neutral line absorbing features in the solar atmosphere may give an important clue to the mechanism whereby both type III solar radiobursts and solar flares are triggered. It is suggested that as new satellite magnetic flux emerges at the edge of an active region in an area of opposite polarity a neutral sheet builds up between the new and old flux. When the sheet has a length of about a megametre its thermal insulation from the surrounding plasma is effective enough for a thermal instability to occur. The resulting compression and inflow of plasma is observed in H on the disc as a neutral line absorbing feature. Furthermore, the electric field of the accompanying collisionless tearing mode instability in a thin slab near the centre of the sheet exceeds the runaway field; it may therefore accelerate electrons to high enough energies to produce the type III burst which usually occurs at the same time as the absorbing feature. Perhaps the flare which sometimes ensues is triggered when the quasi-equilibrium state is destroyed by the development of turbulence in the neutral sheet.     

Problems of Meterwave Spikes

1　ＩｎｔｒｏｄｕｃｔｉｏｎｓＴｈｅｄｉｓｃｏｖｅｒｙｏｆｍｅｔｅｒｗａｖｅ (～ 1 0 - 30 0ＭＨｚ)ｓｐｉｋｅｂｕｒｓｔｓ (ｆａｓｔｄｒｉｆｔｉｎｇｂｕｒｓｔｓｗｉｔｈｖｅｒｙｓｈｏｒｔｄｕｒａｔｉｏｎｓａｔｆｉｘｅｄｆｒｅｑｕｅｎｃｉｅｓ)ｃａｎｂｅｔｒａｃｅｄｂａｃｋｔｏｔｈｅ 1 96 0’ｓｂｙＤｅＧｒｏｏｔａｎｄｔｈｅｉｒｃｈａｒ ａｃｔｅｒｉｓｔｉｃｓｏｆｎａｒｒｏｗ ｂａｎｄ (ｔｈｅｒｅｌａｔｉｖｅｗａｖｅｂａｎｄｉｓｌｅｓｓｔｈａｎａｆｅｗｐｅｒｃｅｎｔ)ａｎｄｖｅｒｙｓｈｏｒｔｅｍｉｓ ｓｉ…     

Decameter studies of the 5 September 1973 flare

We discuss the spectra and positions of the meter-decameter wavelength radio sources associated with the 5 September 1973 flare. We discuss the evolution of the size of the type II burst source and show that it fluctuates by a factor of 10, or larger. Consequently, the potential and kinetic energies associated with the shock are uncertain by the same factor. By comparing the positions of the type II and type III sources we conclude that while the shock wave associated with the type II was guided along high loops, the type III electrons were injected along open field lines which diverged within a short height in the corona. The characteristics of a particularly interesting type III burst with a low-frequency cut-off are discussed. We argue that nearby loops were not disrupted by the shock and that the energetic electrons produced during the event must have been injected at several sites and guided along open field lines at large distances from the flare to produce type III bursts.     

微波毫秒尖峰辐射的时间轮廓

对１９９０年７月３０日云南天文台４波段太阳射电同步观测系统所观测到的大量毫秒级尖峰辐射（ｍｓ－ｓｐｉｋｅｓ）的时间轮廓（包括各种定义的持续时间,上升时间,衰减时间,强度等）作了详细的统计分析,并与米波－长厘米波段的ｓｐｉｋｅ的时间轮廓作了一些比较,以求对微波段的ｓｐｉｋｅ的时间轮廓的特征有一个深入的了解,进而对研究其辐射机制提供有益的帮助     

发生在5月16日太阳耀斑中的微波射电尖峰辐射

对1991年5月16日发生在2.5GHz和2.6 GHz的射电尖峰辐射的持续时间,偏振和准周期振荡等特点作统计分析,详细报导了尖峰辐射的左旋偏振和右旋偏振在2.5,2.6GHz和3.1 GHz上的贡献.在这3个频率上,大量尖峰辐射不仅迭加在微波爆发的上升和极大相上.还迭加在微波爆发的下降相上.值得注意的是,在2.5 GHz和2.6 GHz处,也迭加在发生在主微波爆发后的小爆发上.尖峰辐射持续了17分钟.描述了发生在2.5GHz和2.6 GHz上尖峰辐射的不同时间尺度的偏振反转.统计分析表明在2.5 GHz以及2.6 GHz频率上的尖峰辐射的偏振反转有不同特点,在2.5 GHz频率上的尖峰辐射偏振反转比2.6 GH早1.5分钟,并且在2.5 GHz上尖峰辐射偏振方向反转更多.     

Millisecond Radio Spikes in the Decimetric Band

We present the results of the analysis of thirteen events consisting of dm-spikes observed in Toruń between 15 March 2000 and 30 October 2001. The events were obtained with a very high time resolution (80 microseconds) radio spectrograph in the 1352 – 1490 MHz range. These data were complemented with observations from the radio spectrograph at Ondřejov in the 0.8 – 2.0 GHz band. We evaluated the basic characteristics of the individual spikes (duration, spectral width, and frequency drifts), as well as their groups and chains, the location of their emission sources, and the temporal correlations of the emissions with various phases of the associated solar flares. We found that the mean duration and spectral width of the radio spikes are equal to 0.036 s and 9.96 MHz, respectively. Distributions of the duration and spectral widths of the spikes have positive skewness for all investigated events. Each spike shows positive or negative frequency drift. The mean negative and positive drifts of the investigated spikes are equal to −776 MHz s⁻¹ and 1608 MHz s⁻¹, respectively. The emission sources of the dm-spikes are located mainly at disk center. We have noticed two kinds of chains, with and without frequency drifts. The mean durations of the chains vary between 0.067 s and 0.509 s, while their spectral widths vary between 7.2 MHz and 17.25 MHz. The mean duration of an individual spike observed in a chain was equal to 0.03 s. While we found some agreement between the global characteristics of the groups of spikes recorded with the two instruments located in Toruń and Ondřejov, we did not find any one-to-one relation between individual spikes.     

Observations of the Rosette Nebula using the Decameter Wave Radio Telescope at Gauribidanur

A map of Rosette Nebula in continuum absorption is made at 34.5 MHz using the Decameter Wave Radio Telescoe at Gauribidanur, India, with a resolution of 26×40, is presented. These observations are combined with the 2700 MHz measurements of Grahamet al. (1982) to derive the electron temperature distribution across the nebula. It is found that the temperatures in the southeastern parts of the nebula are around 5000 K and increase up to 8000 K towards the northwestern regions. It is suggested that the lower electron temperatures in the southeastern regions are due to the presence of more dust there compared to other regions in the nebula.     

Decameter solar type III bursts: Data classification with use of cluster analysis

The many-parametric data on decametric type III bursts containing more than 1000 events were classified with use of cluster analysis, i.e., the pattern recognition procedure. For the classification such parameters have been used as intensity, duration and degree of circular polarization derived from burst time profiles. The automatic classification has resulted in division of daily samples of type III bursts into classes of bursts, more homogeneous statistically, which can be associated with different components of type III radiation distinguished by their physical origin. For the classes obtained, statistically reliable dependences of the mean intensity on source position can be found which allow one to conclude about the source structure and evolution, as well as about the characteristics defined by a burst generation mechanism and propagation effects.     

Microwave Millisecond Spikes on July 30, 1997

1　ＯｂｓｅｒｖａｔｉｏｎａｎｄｄａｔａａｎａｌｙｓｅｓＴｈｅｔｉｍｅｐｒｏｆｉｌｅｓｏｆｒａｄｉｏｂｕｒｓｔａｔｔｈｅｆｏｕｒｗａｖｅｌｅｎｇｔｈｓａｒｅｇｉｖｅｎｉｎＦｉｇｕｒｅ 1 .Ｗｅｄｅｆｉｎｅａｓｐｉｋｅａｃｃｏｒｄｉｎｇｔｏｔｗｏｃｒｉｔｅｒｉａ :( 1 )ｔｈｅｄｕｒａｔｉｏｎｉｓｌｅｓｓｔｈａｎ 1 0 0ｍｓａｎｄ ( 2 )ｔｈｅｐｅａｋｆｌｕｘｉｓｗｅｌｌａｂｏｖｅｔｈｅｄｅｔｅｃｔｉｏｎｌｉｍｉｔｏｆ 5σ (σ :ｒｍｓ ,ｄｅｒｉｖｅｄｆｒｏｍｅａｃｈｍｓ ｆｉｌｅ) .Ｔｈｅｎｕｍｂｅｒｓｏｆｓ…