Solar Radio Bursts Research Articles

Chronology of Formation of Solar Radio Burst Types III and V Associated with Solar Flare Phenomenon on 19th September 2011

The formation of two different solar bursts, type III and V in one solar flare event is presented. Both bursts are found on 19th September 2011 associated with C-class flares on active region 1295. From the observation, we believed that the mechanism of evolution the bursts play an important role in the event. It is found that type V burst appeared in five minutes after type III. There are a few active regions on the solar disk but most are magnetically simple and have remained rather quiet. An interpretation of this new result depends critically on the number of sunspots and the role of active region 1295. Sunspot number is increased up to 144 with seven sunspots can be observed. During that event, the speed of solar wind exceeds 433.8 km/second with 2.0 g/cm3 density of protons in the solar corona. Currently, radio flux is also high up to 150 SFU. The solar flare type C6 is continuously being observed in the X-ray region for 24 hours since 1541 UT and a maximum C1 is detected on 1847 UT. Although the sources of both bursts are same, the direction and ejection explode differently. It is believed that the ejection of particles in a type III burst is higher than solar burst type V.

Linear mode conversion of Langmuir/z-mode waves to radiation in plasmas with various magnetic field strength

Linear mode conversion of Langmuir/z waves to electromagnetic radiation near the plasma and upper hybrid frequency in the presence of density gradients is potentially relevant to type II and III solar radio bursts, ionospheric radar experiments, pulsars, and continuum radiation for planetary magnetospheres. Here, we study mode conversion in warm, magnetized plasmas using a numerical electron fluid simulation code when the density gradient has a wide range of angle, δ, to the ambient magnetic field, B0, for a range of incident Langmuir/z wavevectors. Our results include: (1) Left-handed polarized ordinary (oL) and right-handed polarized extraordinary (xR) mode waves are produced in various ranges of δ for Ω0 = (ωL/c)1/3(ωce/ω) < 1.5, where ωce is the (angular) electron cyclotron frequency, ω is the angular wave frequency, L is the length scale of the (linear) density gradient, and c is the speed of light; (2) the xR mode is produced most strongly in the range, 40° < δ < 60°, for intermediately magnetized p...

ELECTRON CYCLOTRON MASER EMISSION IN CORONAL ARCHES AND SOLAR RADIO TYPE V BURSTS

Solar radio type V bursts were classified as a special spectral class based on their moderately long duration, wide bandwidth, and sense of polarization opposite of associated type III bursts. However, type V bursts are also closely related to the preceding type III bursts. They have an approximately equal source height and the same dispersion of position with frequency. Electron cyclotron maser (ECM) instability driven by beam electrons has been used to explain type III bursts in recent years. We propose ECM emission as the physical process of type V solar radio bursts. According to the observed properties of type V and III bursts, we propose that energetic electrons in excited type V continuum are trapped in coronal loops, which are adjacent to the open field lines traced by type III electrons. With the proposed magnetic field configuration and the ECM emission mechanism, the observed properties of type V bursts, such as long duration, wide bandwidth, and opposite sense of polarization can be reasonably explained by our model.

SOLAR TYPE III RADIO BURSTS MODULATED BY HOMOCHROMOUS ALFVÉN WAVES

Solar type III radio bursts and their production mechanisms have been intensively studied in both theory and observation and are believed to be the most important signatures of electron acceleration in active regions. Recently, Wu et al. proposed that the electron-cyclotron maser emission (ECME) driven by an energetic electron beam could be responsible for producing type III bursts and pointed out that turbulent Alfven waves can greatly influence the basic process of ECME via the oscillation of these electrons in the wave fields. This paper investigates effects of homochromous Alfven waves (HAWs) on ECME driven by electron beams. Our results show that the growth rate of the O-mode wave will be significantly modulated by HAWs. We also discuss possible application to the formation of fine structures in type III bursts, such as so-called solar type IIIb radio bursts.

Simultaneous EUV and radio observations of bidirectional plasmoids ejection during magnetic reconnection

We present a multiwavelength study of the X-class flare, which occurred in active region (AR) NOAA 11339 on 3 November 2011. The EUV images recorded by SDO/AIA show the activation of a remote filament (located north of the AR) with footpoint brightenings about 50 min prior to the flare occurrence. The kinked filament rises-up slowly and after reaching a projected height of ~49 Mm, it bends and falls freely near the AR, where the X-class flare was triggered. Dynamic radio spectrum from the Green Bank Solar Radio Burst Spectrometer (GBSRBS) shows simultaneous detection of both positive and negative drifting pulsating structures (DPSs) in the decimetric radio frequencies (500-1200 MHz) during the impulsive phase of the flare. The global negative DPSs in solar flares are generally interpreted as a signature of electron acceleration related to the upward moving plasmoids in the solar corona. The EUV images from AIA 94 \AA reveal the ejection of multiple plasmoids, which move simultaneously upward and downward in the corona during the magnetic reconnection. The estimated speeds of the upward and downward moving plasmoids are ~152-362 and ~83-254 km/s, respectively. These observations strongly support the recent numerical simulations of the formation and interaction of multiple plasmoids due to tearing of the current-sheet structure. On the basis of our analysis, we suggest that the simultaneous detection of both the negative and positive DPSs is most likely generated by the interaction/coalescence of the multiple plasmoids moving upward and downward along the current-sheet structure during the magnetic reconnection process. Moreover, the differential emission measure (DEM) analysis of the active region reveals presence of a hot flux-rope structure (visible in AIA 131 and 94 \AA) prior to the flare initiation and ejection of the multi-temperature plasmoids during the flare impulsive phase.

The effect of solar radio bursts on the GNSS radio occultation signals

AbstractSolar radio burst (SRB) is the radio wave emission after a solar flare, covering a broad frequency range, originated from the Sun's atmosphere. During the SRB occurrence, some specific frequency radio wave could interfere with the Global Navigation Satellite System (GNSS) signals and therefore disturb the received signals. In this study, the low Earth orbit‐ (LEO‐) based high‐resolution GNSS radio occultation (RO) signals from multiple satellites (COSMIC, CHAMP, GRACE, SAC‐C, Metop‐A, and TerraSAR‐X) processed in University Corporation for Atmospheric Research (UCAR) were first used to evaluate the effect of SRB on the RO technique. The radio solar telescope network (RSTN) observed radio flux was used to represent SRB occurrence. An extreme case during 6 December 2006 and statistical analysis during April 2006 to September 2012 were studied. The LEO RO signals show frequent loss of lock (LOL), simultaneous decrease on L1 and L2 signal‐to‐noise ratio (SNR) globally during daytime, small‐scale perturbations of SNR, and decreased successful retrieval percentage (SRP) for both ionospheric and atmospheric occultations during SRB occurrence. A potential harmonic band interference was identified. Either decreased data volume or data quality will influence weather prediction, climate study, and space weather monitoring by using RO data during SRB time. Statistically, the SRP of ionospheric and atmospheric occultation retrieval shows ~4% and ~13% decrease, respectively, while the SNR of L1 and L2 show ~5.7% and ~11.7% decrease, respectively. A threshold value of ~1807 SFU of 1415 MHz frequency, which can result in observable GNSS SNR decrease, was derived based on our statistical analysis.

PREDICTION OF TYPE II SOLAR RADIO BURSTS BY THREE-DIMENSIONAL MHD CORONAL MASS EJECTION AND KINETIC RADIO EMISSION SIMULATIONS

Type II solar radio bursts are the primary radio emissions generated by shocks and they are linked with impending space weather events at Earth. We simulate type II bursts by combining elaborate three-dimensional MHD simulations of realistic coronal mass ejections (CMEs) at the Sun with an analytic kinetic radiation theory developed recently. The modeling includes initialization with solar magnetic and active region fields reconstructed from magnetograms of the Sun, a flux rope of the initial CME dimensioned with STEREO spacecraft observations, and a solar wind driven with averaged empirical data. We demonstrate impressive accuracy in time, frequency, and intensity for the CME and type II burst observed on 2011 February 15. This implies real understanding of the physical processes involved regarding the radio emission excitation by shocks and supports the near-term development of a capability to predict and track these events for space weather prediction.

Callisto radio spectrometer for observing the sun—Metsähovi Radio Observatory joins the worldwide observing network

The radio spectrum at MRO suffers from local electronics, broadband television, DBV-T, FM-radio, and some local data-links of nearby Schengen police communication and hence Metsähovi in the present situation is not ideal as a host site for a solar frequency agile or even to have an FFT spectrometer used at low frequencies. The general situation will be notably improved by installing the whole system at a more remote location or by improving the shielding of nearby electronic equipment. Also during the weekends, RFI-levels seem to be notably lower than during the office hours. Nevertheless it will be possible to detect strong flares with more than 50 sfu. A larger antenna with more gain would improve the situation drastically due to the fact that the signal-to-noise ratio of the solar flares would improve. Also a pre-amplifier with better noise figure and larger gain could improve the whole system's noise temperature. The most harmful interference frequencies are generated by the local electronics. However, during the observations the antenna is pointed away from the laboratory buildings. Thus the spectra is reasonable during observations, especially at higher frequencies (>300 MHz). The first results have shown that the measurement system is operating reliably and it can detect some weak solar radio bursts.

Exact evaluation of the rates of electrostatic decay and scattering off thermal ions for an unmagnetized Maxwellian plasma

Electrostatic decay of Langmuir waves into Langmuir and ion sound waves (L→L′+S) and scattering of Langmuir waves off thermal ions (L+i→L′+i′, also called “nonlinear Landau damping”) are important nonlinear weak-turbulence processes. The rates for these processes depend on the quadratic longitudinal response function α(2) (or, equivalently, the quadratic longitudinal susceptibility χ(2)), which describes the second-order response of a plasma to electrostatic wave fields. Previous calculations of these rates for an unmagnetized Maxwellian plasma have relied upon an approximate form for α(2) that is valid where two of the wave fields are fast (i.e., vϕ=ω/k≫Ve where ω is the angular frequency, k is the wavenumber, and Ve is the electron thermal speed) and one is slow (vϕ≪Ve). Recently, an exact expression was derived for α(2) that is valid for any phase speeds of the three waves in an unmagnetized Maxwellian plasma. Here, this exact α(2) is applied to the calculation of the three-dimensional rates for electrostatic decay and scattering off thermal ions, and the resulting exact rates are compared with the approximate rates. The calculations are performed using previously derived three-dimensional rates for electrostatic decay given in terms of a general α(2), and newly derived three-dimensional rates for scattering off thermal ions; the scattering rate is derived assuming a Maxwellian ion distribution, and both rates are derived assuming arc distributions for the wave spectra. For most space plasma conditions, the approximate rate is found to be accurate to better than 20%; however, for sufficiently low Langmuir phase speeds (vϕ/Ve≈3) appropriate to some spatial domains of the foreshock regions of planetary bow shocks and type II solar radio bursts, the use of the exact rate may be necessary for accurate calculations. The relative rates of electrostatic decay and scattering off thermal ions are calculated for a range of parameters using the exact expressions for the rates; electrostatic decay is found to have the larger growth rate over the whole range of parameters, consistent with previous approximate calculations.

Electrostatic decay of Langmuir/z‐mode waves in type III solar radio bursts

About 40% of the waveforms observed by STEREO during type III solar radio bursts exhibits Langmuir beating and have split spectral peaks, suggestive of decay into product Langmuir and ion‐acoustic waves. For lower electron beam speeds vb/c≲0.1, the spectra of Langmuir events with split spectral peaks are shown to be consistent with electrostatic (ES) decay into Langmuir‐like waves with frequencies above the electron plasma frequency. For faster beam speeds , the spectra are consistent with one or more successive generations of ES decay and an end state of low wave number Langmuir/z‐mode waves with strong electric fields perpendicular to the magnetic field. For many of the split spectral‐peak events, an intense low‐frequency response occurs that is consistent with ion‐acoustic waves produced by ES decay, providing further evidence that these events are ES decay. An observed event is shown to be consistent with three successive backscatter decays, but such events are very rare in type III bursts. About 90% of the split spectral‐peak events occur when Ti/Te≲0.6. Similarly, over 80% of the split peak events have energy densities above the theoretical nonlinear threshold for ES decay (for reasonable Langmuir damping rates ≲10−3ωp). All events have beam speeds and energy densities below the maxima appropriate for ES decay of beam‐driven Langmuir waves.

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 16-28 MHz. The observed radio burst has some unusual properties, which are not typical for the other types of solar radio bursts. The frequency drift rate of it 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 varies from 50 s up to 80 s, depending on the frequency. The maximum radio flux of the unusual burst reaches $\approx 10^3$ s.f.u and its polarization does not exceed 10%. This burst has a fine frequency-time structure of unusual appearance. It consists of stripes with the frequency bandwidth 300-400 kHz. We consider that several accompanied radio and optical events observed by SOHO and STEREO spacecraft are possibly associated with the reported radio burst. A model that may interpret the observed unusual solar radio burst is proposed.

Theoretical Review of Solar Radio Burst III (SRBT III) Associated With of Solar Flare Phenomena

This article broadly reviews our knowledge of theoretical solar radio burst type III (SRBT III) in the low frequency region. The eruption mechanism of solar flares and type III are currently an extremely active area of research especially during the solar cycle is towards maximum. There is a particular focus on their physical properties, as opposed to the microphysics such as that needed for the evolution and formation of this burst or particle acceleration as such. In this work we summarize the related theory, model, significant parameters and relate it with the behavior of the burst in low range frequency. Although this is only a combination of all significant literature, it is hoped that it will give some idea on how to understand in details on this burst

The effect of initial conditions on the electromagnetic radiation generation in type III solar radio bursts

Extensive particle-in-cell simulations of fast electron beams injected in a background magnetised plasma with a decreasing density profile were carried out. These simulations were intended to further shed light on a newly proposed mechanism for the generation of electromagnetic waves in type III solar radio bursts [D. Tsiklauri, Phys. Plasmas, 18, 052903 (2011)]. The numerical simulations were carried out using different density profiles and fast electron distribution functions. It is shown that electromagnetic L and R modes are excited by the transverse current, initially imposed on the system. In the course of the simulations no further interaction of the electron beam with the background plasma could be observed.

Investigation of the Coronal Magnetic Field Using a Type II Solar Radio Burst

The Type-II solar radio burst recorded on 13 June 2010 by the radio spectrograph of the Hiraiso Solar Observatory was employed to estimate the magnetic-field strength in the solar corona. The burst was characterized by a well pronounced band-splitting, which we used to estimate the density jump at the shock and Alfven Mach number using the Rankine-Hugoniot relations. The plasma frequency of the Type-II bursts is converted into height [R] in solar radii using the appropriate density model, then we estimated the shock speed [Vs], coronal Alfven velocity [Va], and the magnetic-field strength at different heights. The relative bandwidth of the band-split is found to be in the range 0.2 -- 0.25, corresponding to the density jump of X = 1.44 -- 1.56, and the Alfven Mach number of MA = 1.35 -- 1.45. The inferred mean shock speed was on the order of V ~ 667 km/s. From the dependencies V(R) and MA(R) we found that Alfven speed slightly decreases at R ~ 1.3 -- 1.5. The magnetic-field strength decreases from a value between 2.7 and 1.7 G at R ~ 1.3 -- 1.5 Rs depending on the coronal-density model employed. We find that our results are in good agreement with the empirical scaling by Dulk and McLean (Solar Phys. 57, 279, 1978) and Gopalswamy et al. (Astrophys. J. 744, 72, 2012). Our result shows that Type-II band splitting method is an important tool for inferring the coronal magnetic field, especially when independent measurements were made from white light observations.

Langmuir “snakes” and electrostatic decay in the solar wind

When Langmuir waves are driven by an electron beam to large amplitudes, they can undergo electrostatic (ES) decay to smaller wave numbers via a series of backscatters. Truncated ES decay, where the number of backscatters is reduced due to damping, is modeled here using the three‐dimensional ES Zakharov equations. Langmuir beats develop in “snake”‐like structures parallel to the electron beam direction and are most evident when decay is truncated to a single backscatter. From these results, an analytic form is derived and shown to be consistent with some of the waveforms and spectra observed by STEREO in the source regions of type III solar radio bursts. The agreement between the model and observations provides strong evidence for ES decay and Langmuir “snakes” parallel to the electron beam and so the ambient magnetic field.

Impact of the 24 September 2011 solar radio burst on the performance of GNSS receivers

Intense solar radio bursts occurring at the L‐band frequencies can significantly impact the performance of Global Navigation Satellite System (GNSS) receivers in the sunlit hemisphere of the Earth. An intense solar radio burst occurred on 24 September 2011, with a maximum power of 110,000 solar flux units (10−22 W/m2/Hz) at 1.415 GHz. This manuscript aims to contribute insight on the impact of this solar radio burst on the performance of the GNSS receivers in the European and Latin American sectors. Maximum reductions of 11.0, 22.0, and 10.0 dB Hz in the carrier‐to‐noise density ratio (C/N0) of the GPS L1C/A, L2P, and L2C signals, respectively, were observed. The C/N0 reduction is modulated by the local solar incidence angle for the GPS L1C/A and L2P signals, whereas such modulation was not observed for the GPS L2C signal. The solar radio burst also had an adverse effect on the recorded GNSS pseudorange and carrier phase data, thereby causing positioning errors, which are also presented herein.

Book Review: The First Woman Radio Astronomer, under the Radar: The First Woman in Radio Astronomy, Ruby Payne-Scott

Book Reviews more generally throughout the volume, it would have been extremely useful had she at least brought the relevant bibliography up to date. A survey of this sort from 1987 is only valuable in 2013 up to a certain point; but to translate and re-publish without bringing either the analysis or the bibliography up to date seems a wasted opportunity. Closer proofreading by a native English speaker on several essays would also have been appreciated. University of Nevada, Reno H. D arrel R utkin THE FIRST WOMAN RADIO ASTRONOMER Under the Radar: The First Woman in Radio Astronomy, Ruby Payne-Scott. W. M. Goss and Richard X. McGee (Springer, Berlin, 2010). Pp. xxii + 354. €128. ISBN She loved bush walking, cats, and radio engineering; was briefly a member of the Communist Party of Australia; and discovered or co-discovered at least three of the four kinds of radio burst emission from the Sun. She was Ruby Payne-Scott (1912–81), the first woman radio astronomer in Australia and, very probably, in the world. Despite this, she is almost forgotten in the astronomical community, even its radio part. Reading this book raised for me several questions. First, why did Payne-Scott not leave a more visible footprint? The authors men- tion several contributing factors: her gender and lack of Ph.D. in a community where academic credentials were becoming common as radar work gave way to astronomy; several more prominent colleagues who were not very fond of her (although John Bolton later spoke highly of her work); and her definitive departure from the radio astronomy community in 1951, about four months before the birth of her first child. She never returned, taking up high school teaching when her children were 10 and 12. This meant that she was not around later to cite her own early papers! Less clear from the book is that rapid advances in radio telescopes, detectors, and data- processing soon swamped her contributions, which included early development of interferometry and aperture synthesis and the recognition that confusion was a more serious problem than low sensitivity for the radio telescopes of the time, as well as the discovery of and attempts to characterize the various types of solar radio bursts. Second, do we need to know more about Payne-Scott, her life and her work? The authors clearly think so, since they have worked long and hard to track down primary sources in Australian archives and to interview many people (often just in the nick of time) who knew her. The oddest omission, I think, is Frank J. Kerr (1918–2000) who appears on at least 17 pages and in several photographs of Payne-Scott but who was not interviewed and does not even make the index. Kerr was an active member of the Australian radar and radio astronomy communities, almost from the begin- ning, and later a co-founder of the University of Maryland radio astronomy group, where I knew him. Downloaded from jha.sagepub.com at UNIV CALIFORNIA SAN DIEGO on May 6, 2015

Deterministic behaviour in the dynamics of solar metric radio bursts with intermediate drifting patterns

The dynamic characteristics of solar metric radio bursts with intermediate drifting patterns (fiber bursts) as they evolve at fixed frequency are examined. The data were recorded using the radio polarimeter of the Trieste Astronomical Observatory. The aim is to determine if the underlying process can be described as a deterministic chaos. Correlation dimensions and Hurst exponent are estimated showing deterministic chaotic system of low dimension.

PEAK FLUX DISTRIBUTIONS OF SOLAR RADIO TYPE-I BURSTS FROM HIGHLY RESOLVED SPECTRAL OBSERVATIONS

Solar radio type-I bursts were observed on 2011 January 26 by high resolution observations with the radio telescope AMATERAS in order to derive their peak flux distributions. We have developed a two-dimensional auto burst detection algorithm that can distinguish each type-I burst element from complex noise storm spectra that include numerous instances of radio frequency interference (RFI). This algorithm removes RFI from the observed radio spectra by applying a moving median filter along the frequency axis. Burst and continuum components are distinguished by a two-dimensional maximum and minimum search of the radio dynamic spectra. The analysis result shows that each type-I burst element has one peak flux without double counts or missed counts. The peak flux distribution of type-I bursts derived using this algorithm follows a power law with a spectral index between 4 and 5.

Solar Energetic Electrons, X‐Rays, and Radio Bursts

We review recent results on solar energetic electrons observed in situ near 1 AU, and on the radio and X-ray emission generated by these electrons. Near solar maximum, hundreds of solar impulsive electron events are detected per year by the Wind spacecraft. About ∼10% are prompt events, where the electrons at all energies are injected from the Sun at the time of the solar type III radio burst, but in the rest the injection of tens of keV electrons is delayed by ∼10 minutes. For prompt events with associated flare hard X-ray (HXR) emission, the electron spectrum measured at 1 AU shows a rough correlation with that of the HXR-producing electrons at the Sun, but the correlation does not fit a simple thick or thin target model. Recent analysis of several scatter-free events detected from ∼0.4 to 300 keV show that they involve two separate injections, the low energy, ∼0.4 to ∼10 keV electron injection starts prior to the type III burst, while >13 keV electrons are injected ∼10 minutes afterwards. The electron, radio and in situ plasma wave observations are all consistent with the type III radio emission being produced by ∼0.4 - 10 keV electrons. Finally, RHESSI has detected weak HXR bursts that may be a signature of the type III burst acceleration itself and not associated with flares.