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.     

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.     

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.     

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.     

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.     

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.     

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。     

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．     

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.     

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.     

Interplanetary Nanodust Detection by the Solar Terrestrial Relations Observatory/WAVES Low Frequency Receiver

New measurements using radio and plasma-wave instruments in interplanetary space have shown that nanometer-scale dust, or nanodust, is a significant contributor to the total mass in interplanetary space. Better measurements of nanodust will allow us to determine where it comes from and the extent to which it interacts with the solar wind. When one of these nanodust grains impacts a spacecraft, it creates an expanding plasma cloud, which perturbs the photoelectron currents. This leads to a voltage pulse between the spacecraft body and the antenna. Nanodust has a high charge/mass ratio, and therefore can be accelerated by the interplanetary magnetic field to the speed of the solar wind: significantly faster than the Keplerian orbital speeds of heavier dust. The amplitude of the signal induced by a dust grain grows much more strongly with speed than with mass of the dust particle. As a result, nanodust can produce a strong signal despite its low mass. The WAVES instruments on the twin Solar TErrestrial RElations Observatory spacecraft have observed interplanetary nanodust particles since shortly after their launch in 2006. After describing a new and improved analysis of the last five years of STEREO/WAVES Low Frequency Receiver data, we present a statistical survey of the nanodust characteristics, namely the rise time of the pulse voltage and the flux of nanodust. We show that previous measurements and interplanetary dust models agree with this survey. The temporal variations of the nanodust flux are also discussed.     

Evidence for a Strong Correlation of Solar Proton Events with Solar Radio Bursts

A statistical analysis is made on the correlation between solar proton events with energies >10Mev and solar radio bursts during the four-year period from 1997 November to 2000 November. We examine 28 solar proton events and their corresponding solar radio bursts at 15400, 8800, 4995, 2695, 1415, 606, 410 and 245 MHz. The statistical result shows that there is a close association between solar proton events and ≥3 solar radio bursts occurring at several frequencies, one or two days before. In particular, it is noteworthy that proton events occurring     

High-Latitude Inner Solar Wind from Pulsar Radio Sounding Observations

Radio sounding experiments probing the inner solar wind by polarized pulses of pulsars PSR B0525+21 (J0528+22) and PSR B531+21 (J0534+22) were carried out in June 2005 and June 2007 on the large phased array of the Lebedev Physical Institute at 111 MHz in the period near the minimum of the solar-activity cycle. The lines of sight toward these pulsars were close to the Sun during the observation sessions. The arrival-time delays for pulses from PSR J0534+22 are used to derive the radial dependence of the mean density of the circumsolar plasma. Comparison with Stanford coronal magnetic-field data, STEREO SECCHI, and SOHO EIT synoptic maps shows that the results are related to the polar coronal holes. The ambient density radial distribution derived from the arrival-time delays for pulses from PSR J0534+22 is stronger than inverse-square law indicating that the acceleration of fast, high-latitude solar-wind outflows, continues to heliocentric distances of (5–10)R _S, where R _S is the solar radius. The mean plasma density near a solar-activity minimum in the investigated range of heliocentric distances is substantially lower than at the solar-activity maximum.     

云南天文台40米射电望远镜河外射电源观测

为了在云南天文台40 m天线上开展射电天文研究,使用它进行了河外射电源流量试观测。通过对河外致密源进行ON/OFF跟踪观测,得到射电源的流量变化曲线。但数据质量并不理想,说明系统存在一些问题。随后,根据对该望远镜系统的稳定性及其无线电环境干扰现状的考察,以及对现存问题的分析,提出了相应的解决方法。     

EUV and Magnetic Activities Associated with Type-I Solar Radio Bursts

Type-I bursts (i.e. noise storms) are the earliest-known type of solar radio emission at the meter wavelength. They are believed to be excited by non-thermal energetic electrons accelerated in the corona. The underlying dynamic process and exact emission mechanism still remain unresolved. Here, with a combined analysis of extreme ultraviolet (EUV), radio and photospheric magnetic field data of unprecedented quality recorded during a type-I storm on 30 July 2011, we identify a good correlation between the radio bursts and the co-spatial EUV and magnetic activities. The EUV activities manifest themselves as three major brightening stripes above a region adjacent to a compact sunspot, while the magnetic field there presents multiple moving magnetic features (MMFs) with persistent coalescence or cancelation and a morphologically similar three-part distribution. We find that the type-I intensities are correlated with those of the EUV emissions at various wavelengths with a correlation coefficient of 0.7?–?0.8. In addition, in the region between the brightening EUV stripes and the radio sources there appear consistent dynamic motions with a series of bi-directional flows, suggesting ongoing small-scale reconnection there. Mainly based on the induced connection between the magnetic motion at the photosphere and the EUV and radio activities in the corona, we suggest that the observed type-I noise storms and the EUV brightening activities are the consequence of small-scale magnetic reconnection driven by MMFs. This is in support of the original proposal made by Bentley et al. (Solar Phys. 193, 227, 2000).     

云南天文台太阳射电频谱仪的网络系统

介绍云南天文台太阳射电米波 (2 30～ 30 0MHz)、分米波 (0 .7～0 .4GHz)频谱观测系统及 1 0m射电望远镜自动控制系统“星型拓扑”对等网的建立。通过该网络 ,不但实现了光盘刻录机、激光打印机等资源共享 ,而且还为解决由于太阳射电频谱高时间分辨率和高频率分辨率观测带来的大数据量处理和存储找到了解决途径