Multipoint Observations of Solar Type III Radio Bursts from STEREO and Wind

The twin STEREO and the Wind spacecraft make remote multipoint measurements of interplanetary radio sources of solar origin from widely separated vantage points. One year after launch, the angular separation between the STEREO spacecraft reached 45°, which was ideal for locating solar type III radio sources in the heliosphere by three-spacecraft triangulation measurements from STEREO and Wind. These triangulated source locations enable intrinsic properties of the radio source, such as its beaming characteristics, to be deduced. We present the first three-point measurements of the beaming characteristics for two solar type III radio bursts that were simultaneously observed by the three spacecraft in December of 2007 and in January of 2008. These analyses suggest that individual type III bursts exhibit a wide beaming pattern that is approximately beamed along the direction tangent to the Parker spiral magnetic field line at the source location.     

Observations and Research on the Solar Radio Spectrum at Yunnan Observatory

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High Temporal and Spectral Resolution Interferometric Observations of Unusual Solar Radio Bursts

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.     

Multiple Type II Solar Radio Bursts

We report on the detailed analysis of a set of 38 multiple type II radio bursts observed by Culgoora radio spectrograph from January 1997 to July 2003. These events were selected on the basis of the following criteria: (i) more than one type II were reported within 30 min interval, (ii) both fundamental and harmonic were identified for each of them. The X-ray flares and CMEs associated with these events are identified using GOES, Yohkoh SXT, SOHO/EIT, and SOHO/LASCO data. From the analysis of these events, the following physical characteristics are obtained: (i) In many cases, two type IIs with fundamental and harmonic were reported, and the time interval between the two type IIs is within 15 min; (ii) The mean values of starting frequency, drift rate, and shock speed of the first type II are significantly higher than those of the second type II; (iii) More than 90% of the events are associated with both X-ray flares and CMEs; (iv) Nearly 75% of the flares are stronger than M1 X-ray class and 50% of CMEs have their widths larger than 200^∘ or they are halo CMEs; (v) While most of the first type IIs started within the flare impulsive phase, 22 out of 38 second type IIs started after the flare impulsive phase. Weak correlations are found between the starting and ending frequencies of these type II events. On the other hand, there was no correlation between two shock speeds between the first and the second type II. Since most of the events are associated with both the flares and CMEs, and there are no events which are only associated with multiple impulsive flares or multiple mass ejections, we suggest that the flares and CMEs (front or flank) both be sources of multiple type IIs. Other possibilities on the origin of multiple type IIs are also discussed.     

A Remark on the Statistical Distribution of the Frequency Range of Solar Radio Bursts

It is shown that for burst bandwidth B considered in the time-frequency domain, the distribution of w(B ⁻¹) is the probability density of radiation of radio emission of a given relative frequency bandwidth, while the distribution w(B) is the density of bursts, arrangement on axis B. Using this remark, we find that solar decimetric spikes and type III bursts, and metric noise storms, have a `radiation probability' approximately 10 times higher for large-bandwidth bursts than for small-bandwidth bursts.     

Bidirectional Type III Solar Radio Bursts

Bidirectional coronal type III bursts are modeled by combining a model of coronal electron heating and beam generation via time-of-flight effects with semiquantitative estimates of quasilinear relaxation. Electromagnetic emissivities are estimated by extending the recently developed theory of interplanetary type III bursts to coronal emissions, including its features of stochastic Langmuir-wave growth and three-wave interactions. The results are investigated for heating on open and closed coronal field lines and are compared with observations of normal, reverse-slope, bidirectional, and inverted-J and -U coronal type III radio bursts. Harmonic emission is predicted to dominate at plasma frequencies above roughly 100 MHz where the efficiency of fundamental emission falls off steeply, while its free-free reabsorption rises. The model also explains the observed trends in the likelihood of occurrence of normal, reverse-slope, and bidirectional coronal type III bursts.     

Wavelet Decomposition of Submillimeter Solar Radio Bursts

We present the results of wavelet decomposition of fast-time structures during four solar flares observed by the Solar Submillimeter-wave Telescope at 212 GHz. The result of the analysis shows (1) observational evidence on the existence of submm-emission time variations in the range from a few tens of millisecond up to few seconds during solar flares, and (2) that when a solar flare is in progress the time scales reduce as the bulk of the emission flux time variations is increasing.     

太阳射电分米波尖峰辐射和米波射电爆发

本文分析了云南天文台四波段快速采样射电望远镜在1990年1月至1991年3月间记录到的毫秒级尖峰辐射事件。结合此期间S.G.D.公布的米波射电大爆发资料,给出了毫秒级尖峰辐射的各种特征,总结出毫秒级尖峰辐射同Ⅲ型、Ⅱ型和Ⅳ型太阳射电爆发的关系,最后做出了相应的解释和讨论。     

Solar Radio Bursts on 16 February 1999

The 2.60–3.80 GHz spectrometer at the Beijing Astronomical Observatory (BAO) recorded a ‘decimetric pulsation’ event (DCIM) around the time 1999 0216 0300. At the beginning and end of this DCIM, two groups of reverse slope type III bursts (RS-III) are also detected; meanwhile, metric type II bursts are recorded by CULG and HIRA during the same time. These solar radio bursts on that day might be caused by the same active region 8458 and a same flare. We present a plausible qualitative model for all of them. This revised version was published online in July 2006 with corrections to the Cover Date.     

Resonant Transition Radiation and Solar Radio Bursts

This paper presents general relations for the intensity of the resonant transition radiation (RTR) and their detailed analysis. This analysis shows that the spectrum amplitude of the x-mode at some frequencies for high-energy electrons can grow with the magnetic field increase in some interval from zero value; it can even dominate over that for the o-mode. With further magnetic field increase, the intensity of the RTR x-mode decreases in comparison with the intensity of the o-mode and this decrease is higher for higher velocities of energetic electrons. The polarization of the RTR depends on the velocity of energetic electrons, too. For velocities lower than some velocity limit v<v _i the RTR emission is unpolarized in a broad interval of magnetic field intensities in the radio source. For reasonable values of indices of the power-law distribution functions of energetic electrons, the RTR is broadband in frequencies (df/f≈0.2−0.4). Furthermore, we show various dependencies of the RTR and its spectral characteristics. Assuming the same radio flux of the transition radiation and the gyro-synchrotron one at the Razin frequency, we estimate the limit magnetic field in the radio source of the transition radiation. Then, we analyze possible sources of small-scale inhomogeneities (thermal density fluctuations, Langmuir and ion-sound waves), which are necessary for the transition radiation. Although the small-scale inhomogeneities connected with the Langmuir waves lead to the plasma radiation, which is essentially stronger than RTR, the inhomogeneities of the ion-sound waves are suitable for the RTR without any other radiation. We present the relations describing the RTR for anisotropic distribution functions of fast electrons. We consider the distribution functions of fast electrons in the form of the Legendre polynomials which depend on the pitch-angle. We analyze the influence of the degree of the anisotropy (an increase of the number of terms in the Legendre polynomial) on spectral characteristics of the RTR. A comparison with previous studies is made. As an example of the use of the derived formulas for the RTR, the 24 December 1991 event is studied. It is shown that the observed decimetric burst can be generated by the RTR in the plasma with the density inhomogeneities at the level 〈ΔN ²〉/N ²=2.5⋅10⁻⁵.     

Statistical Survey of Type III Radio Bursts at Long Wavelengths Observed by the Solar TErrestrial RElations Observatory (STEREO)/Waves Instruments: Radio Flux Density Variations with Frequency

We have performed a statistical study of 152 Type III radio bursts observed by Solar TErrestrial RElations Observatory (STEREO)/Waves between May 2007 and February 2013. We investigated the flux density between 125 kHz and 16 MHz. Both high- and low-frequency cutoffs were observed in 60 % of events, suggesting an important role of propagation. As already reported by previous authors, we observed that the highest flux density occurs at 1 MHz on both spacecraft. We developed a simplified analytical model of the flux density as a function of radial distance and compared it with the STEREO/Waves data.     

Fine Time Structures in Solar Radio Bursts: A Summary of Observations at Four Frequencies

29 fine time structures (FTS) are found in 103 radio bursts observed with YRSOS of high temporal resolution of 1 ms at 4 frequencies (1.42, 2.00 (or2.13), 2.84 and 4.00 (or 4.26) GHz) from January 1990 to January 1994. The various morphologies of FTSs occurring in different phases of flares and the different FTS in the same event may reflect the transitional property of the low-frequency microwave bursts. Most FTSs are probably consisted with the four characteristics observed previously in literatures. The typical and representative events of FTSs and occurrence frequency of each kind are presented in order to explain the multiplicity, breadth and observational characteristics of FTSs in the range of long centimeter to short decimeter wavelengths. This revised version was published online in July 2006 with corrections to the Cover Date.     

太阳射电爆发现象中的电子回旋脉泽辐射

太阳射电爆发(Solar Radio Burst, SRB)是太阳高能电子与背景等离子体相互作用产生的感应辐射现象,其多样的动力学谱类型及其复杂的精细结构反映了辐射源区磁等离子体结构状态丰富的物理信息,而相关辐射机制则是解读相关物理信息的关键工具.长期以来,在SRB辐射机制的研究中一直存在着争议不决的两种主要机制,即等离子体辐射机制和电子回旋脉泽(Electron Cyclotron Maser, ECM)辐射机制.近年来,针对传统的ECM辐射机制应用到SRB现象时遇到的一些主要困难,发展了由幂律谱电子低能截止驱动和包含快电子束自生阿尔文波效应的新型ECM驱动模型,并成功应用于解释各类不同SRB动力学谱的形成机制.基于这些新型的ECM辐射模型,系统地总结了ECM辐射机制在各种不同类型SRB现象中的应用,并对它们不同动力学谱结构的形成给出了一致统一的物理解释.     

Peak Frequency Dynamics in Solar Microwave Bursts

We analyze the dynamics of the broadband frequency spectrum of 338 microwave bursts observed in the years 2001?–?2002 with the Owens Valley Solar Array. A subset of 38 strong microwave bursts that show a single spectral maximum are studied in detail. Our main goal is to study changes in spectral peak frequency ν _pk with time. We show that, for a majority of these simple bursts, the peak frequency shows a high positive correlation with flux density – it increases on the rise phase in ≈83% of 24 bursts where it could be cleanly measured, and decreases immediately after the peak time in ≈62% of 34 bursts. This behavior is in qualitative agreement with theoretical expectations based on gyrosynchrotron self-absorption. However, for a significant number of events (≈30?–?36%) the peak frequency variation is much smaller than expected from self-absorption, or may be entirely absent. The observed temporal behavior of ν _pk is compared with a simple model of gyrosynchrotron radio emission. We show that the anomalous behavior is well accounted for by the effects of Razin suppression, and further show how an analysis of the temporal evolution of ν _pk can be used to uniquely determine the relative importance of self-absorption and Razin suppression in a given burst. The analysis technique provides a new, quantitative diagnostic for the gyrosynchrotron component of solar microwave bursts. Applying this analysis technique to our sample of bursts, we find that in most of the bursts (60%) the spectral dynamics of ν _pk around the time of peak flux density is caused by self-absorption. On the other hand, for a significant number of events (≈70%), the Razin effect may play the dominant role in defining the spectral peak and dynamics of ν _pk, especially on the early rise phase and late decay phase of the bursts.     

日食的射电观测(英)

日食为射电天文提供了一维高空间分辨率太阳射电观测机会．日食射电观测在太阳射电物理的发展上起过重要的作用．文中对日食射电观测的若干重要因素作了介绍和分析．日食射电观测在我国太阳射电天文发展上也起了重要作用．文中简要介绍了在我国组织观测的1958年、1968年、1980年及1987年的太阳射电日食观测及其主要结果．     

云南天文台太阳射电研究进展

回顾了自１９７９年以来云南天文台太阳射电天文仪器、技术和方法以及研究方面的进展。     

Generation of Type U Bursts in Solar Radio Emission

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.     

太阳射电爆发与高能质子加速过程

根据近年来地面和空间观测资料的统计分析指出：（１）太阳质子事件（或质子耀斑）的发生同起伏剧烈的强微波爆发（包括脉冲和ＩＶμ型爆发）或短分米波ＩＶ型爆发存在着紧密的共生关系（共生率趋近１００％）；（２）约有２４％—３０％的质子事件没有对应的ＩＩ型爆发。这一结果否定了以前认为ＩＩ型爆发中的激波加速是产生质子事件必要条件的看法，进而论证了产生强微波（脉冲或ＩＶ＿μ型）爆发的相对论性电子（≥５００ｋｅｖ）与质子耀斑中的高能质子（＞１０ＭｅＶ）都是在耀斑脉冲相的磁环中受到随机ＭＨＤ湍动加速作用而产生的。那些逃逸到行星际空间的质子流就构成了太阳质子事件。     

太阳二十二周峰年云南天文台四波段射电同步观测结果

本文主要介绍云南天文台“四波段太阳射电高时间分辨率同步观测系统”（１．４２，２．１３，２．８４和４．２６ＧＨｚ）１９８９年１２月至１９９３年４月观测事件的统计结果，对１０２个射电爆发进行了初步分析，着重揭示几个类别典型事件的时间轮廓，说明射电高时间分辨率观测的意义。