type-III Bursts Research Articles

Element abundance and the physics of solar energetic particles

The acceleration and transport of solar energetic particles (SEPs) cause their abundance, measured at a constant velocity, to be enhanced or suppressed as a function of the magnetic rigidity of each ion, and hence, of its atomic mass-to-charge ratio of A/Q. Ion charges, in turn, depend upon the source electron temperature. In small “impulsive” SEP events, arising from solar jets, acceleration during magnetic reconnection causes steep power-law abundance enhancements. These impulsive SEP events can have 1,000-fold enhancements of heavy elements from sources at ∼2.5 MK and similar enhancements of 3He/4He and of streaming electrons that drive type-III radio bursts. Gamma-ray lines show that solar flares also accelerate 3He-rich ions, but their electrons and ions remain trapped in magnetic loops, so they dissipate their energy as X-rays, γ-rays, heat, and light. “Gradual” SEPs accelerated at shock waves, driven by fast coronal mass ejections (CMEs), can show power-law abundance enhancements or depressions, even with seed ions from the ambient solar corona. In addition, shocks can reaccelerate seed particles from residual impulsive SEPs with their pre-existing signature heavy-ion enhancements. Different patterns of abundance often show that heavy elements are dominated by a source different from that of H and He. Nevertheless, the SEP abundance, averaged over many large events, defines the abundance of the corona itself, which differs from the solar photosphere as a function of the first ionization potential (FIP) since ions, with FIP <10 eV, are driven upward by forces of electromagnetic waves, which neutral atoms, with FIP >10 eV, cannot feel. Thus, SEPs provide a measurement of element abundance in the solar corona, distinct from solar wind, and may even better define the photosphere for some elements.

The 18–19 March 2022 series of 3He-rich events observed by Solar Orbiter at 0.36 au compared with EUV, X-ray, and radio observations

Context. During the first close perihelion pass of Solar Orbiter, a series of impulsive 3He-rich solar particle events was observed on 18–19 March 2022 from a distance of 0.36 au. In addition to the energetic particle, radio, and X-ray data from Solar Orbiter, the events were observed in radio and/or extreme ultraviolet by STEREO-A, SDO, Wind, and Parker Solar Probe. Aims. Observations of the event series along with remote sensing of flaring and radio emission with only small timing delays due to the close distance allow the association with energetic particles to be determined with much higher accuracy than previously possible from 1 au. Methods. By comparing the onsets of type-III bursts with the arrival of electrons of tens of keV at Solar Orbiter only a few minutes later, it can be seen that, overall, each of the more intense type-III bursts was associated with an electron and ion injection. Extreme ultraviolet data show that the times of the type-III bursts coincide with emission from a small (approximately Earth-sized) loop to the west of a nearby active region. Results. The energetic particle spectra and abundances show typical properties of impulsive 3He-rich flares and, when combined with the remote sensing observations, establish that the particle-accelerating mechanism in this series of events operates near the solar surface in association with magnetic loops, and in the absence of other phenomena such as jets and small coronal mass ejections.

Simulating Solar Radio Bursts Using Generative Adversarial Networks

Solar flares are one of the most extreme drivers of space weather in our solar system. The impulsive solar radio emission associated with a solar flare is known as a solar radio burst (SRB). They are generally studied in dynamic spectra and are classified into five major spectral classes, ranging from Type I to Type V, based on their form and frequency, and time duration. Due to their intricate characterisation, generating a training set for object-detection and classification models of such phenomena is a difficulty in machine learning. Current algorithms implement parametric modelling where the quantity, grouping, intensity, drift rate, heterogeneity, start–end frequency and start–end time of Type-III and Type-II radio bursts are all random. However, this model does not factor in the true shape or general features seen in real dynamic spectra observations of the Sun, which can be crucial when training classification or object-detection algorithms. In this research, we introduce a methodology named a Generative Adversarial Network (GAN) for generating realistic SRB simulations. By using real examples of Type-III and Type-II SRB data, we can train GANs to generate images almost comparable to real observed data. Furthermore, we evaluate the results of the generated model using human perception, then we compare and contrast the results using a metric known as the Fréchet Inception Distance.

Decimetric Type-U Solar Radio Bursts and Associated EUV Phenomena on 2011 February 9

Abstract A GOES M1.9 flare took place in active region AR 11153 on 2011 February 9. With a resolution of 200 kHz and a time cadence of 80 ms, the reverse-drifting (RS) type-III bursts, intermittent sequence of type-U bursts, drifting pulsation structure (DPS), and fine structures were observed by the Yunnan Observatories Solar Radio Spectrometer (YNSRS). Combined information revealed by the multiwavelength data indicated that after the DPS was observed by YNSRS, the generation rate of type-U bursts suddenly increased to 5 times what it had been. In this event, the generation rate of type-U bursts may depend on the magnetic-reconnection rate. Our observations are consistent with previous numerical simulation results. After the first plasmoid produced (plasma instability occurred), the magnetic-reconnection rate suddenly increased by 5 to 8 times. Furthermore, after the DPS, the frequency range of the turnover frequency of type-U bursts was obviously broadened to thrice what it was before, which indicates a fluctuation amplitude of the density in the loop top. Our observations also support numerical simulations during the flare-impulsive phase. Turbulence occurs at the top of the flare loop and the plasmoids can trap nonthermal particles, causing density fluctuation at the loop top. The observations are generally consistent with the results of numerical simulations, helping us to better understand the characteristics of the whole physical process of eruption.

Characterising coronal turbulence using snapshot imaging of radio bursts in 80–200 MHz

Context. Metrewave solar type-III radio bursts offer a unique means to study the properties of turbulence across coronal heights. Theoretical models have shown that the apparent intensity and size of the burst sources evolve at sub-second scales under the influence of local turbulence. The properties of the evolution vary with observation frequency. However, observational studies remained difficult due to the lack of high fidelity imaging capabilities at these fine temporal scales simultaneously across wide spectral bands. Aims. I present a spectroscopic snapshot imaging (0.5 s, 160 kHz resolution) study of a type-III burst event across the 80–200 MHz band. By modelling the temporal variability of the source sizes and intensity at every observation frequency, the characteristics of coronal turbulence are studied across a heliocentric height range of ≈1.54–1.75 R⊙. Methods. To understand the morphological evolution of the type-III source, a 2D Gaussian fitting procedure is used. The observed trends in the source area and integrated flux density are analysed in the framework of theoretical and data-driven models. Results. The strength of density fluctuations (δN/N) in the corona is derived as a function of height (R). Combined with the archival low frequency data, δN/N values across ≈1.5–2.2 R⊙ agree within a few factors. The burst decay time (τdecay) and the full width at half maximum of the source showed a power-law dependence with frequency, roughly consistent with the results from data-driven models. However, the values of τdecay across frequencies turned out higher than the expected trend. The intrinsic sizes of the burst source were derived, correcting for scatter broadening. This roughly matched the expected size of flux tubes at the coronal heights explored. I also report the observation of an intrinsic anti-phased pulsation in the area and flux density of the source.

Temporal and Spatial Association Between a Solar Flare, CME, and Radio Burst on 19 November 2013

We present multi-wavelength and multi-instrument observations and analysis of a major X 1.0 class flare, radio burst, halo coronal mass ejection (CME), and loop eruption from the solar active region NOAA 11893 on 19 November 2013 (SOL2013-11-19T10:26). The aim of this work is twofold: The first aim to study the evolution of the loop eruption and the second is to find the link between this eruption and radio emissions. Initial signatures of eruption from the solar source region are confirmed using observations from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory in the hot channel at 94 A wavelength. These observations confirm that the source of the CME was associated with a magnetic-loop eruption, which was visible before the flare initiation. The photospheric magnetic configuration displayed a complex network of $\upbeta \updelta $ sunspots. After the eruption, a CME was observed by the Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph with linear speed and acceleration of $740~\text{km}\,\text{s}^{-1}$ and $-2~\text{m}\,\text{s}^{-2}$ , respectively. Dynamic radio-spectrum observation from the Learmonth Observatory in the metric frequency range shows Type-III and Type-II radio emissions that reveal the field-line opening and coronal-shock formation closely associated with the CME. From the metric Type-II radio observation and assuming Newkirk’s density model, we estimate the shock formation height range of $1.14\,\text{--}\,1.54~\text{R}_{\odot }$ with the corresponding shock speed ( $\approx650~\text{km}\,\text{s}^{-1}$ ). With the heliographic observations from the Nancay heliograph at different frequencies we could disentangle Type-II bursts from Type-III bursts. Likely, the Type-III burst would correspond to the loop eruption while the Type-II comes from the northern flank of the CME.

Type-III Electron Beams: 3D Quasilinear Effects

A conventional model for the generation of Langmuir waves in Type-III radio bursts is based on a one-dimensional (1D) version of the quasilinear equations. In this model a wave with phase velocity $v_{\phi }$ resonates with an electron with velocity $v=v_{\phi }$ , causing the waves to grow at a rate $\propto {\mathrm{d}}F(v)/{\mathrm{d}}v>0$ , where $F(v)$ is the 1D-distribution function. The backreaction on the electrons drives the electrons towards a plateau distribution: $\mathrm{d}F(v)/{\mathrm{d}}v\to 0$ . In the 3D-generalization, none of these features apply: waves with phase speed $v_{\phi }$ can resonate with electrons with speed $v< v_{\phi }$ , depending on the angle between the wave normal and the electron velocity, wave growth occurs only if the distribution function is both an increasing function of $v$ and also has an anisotropic pitch-angle distribution, and the backreaction involves diffusion in both speed $v$ and in pitch-angle $\alpha $ . In this article we discuss implications of the generalization from 1D to 3D on models for Type-III bursts. An effect that is absent in 1D, but may be important in 3D, is scattering of Langmuir waves by turbulence in the ambient plasma. Pitch-angle scattering by the scattered Langmuir waves may play an important role in the evolution of the Type-III beam.

The growth of the longitudinal beam–plasma instability in the presence of an inhomogeneous background

We study the longitudinal stability of beam–plasma systems in the presence of a density inhomogeneity in the background plasma. Previous works have focused on the non-relativistic regime where hydrodynamical models are used to evolve pre-existing Langmuir waves within inhomogeneous background plasmas. Here, for the first time we study the problem with kinetic equations in a fully relativistic way. We do not assume the existence of Langmuir waves, and we focus on the rate and the mechanism by which waves are excited in such systems from an initial perturbation. We derive the structure of the unstable modes and compute an analytical approximation for their growth rates. Our computation is limited to dilute and cold beams, and shows an excellent agreement with particle-in-cell simulations performed using the SHARP code. We show that, due to such an inhomogeneity, the virulent beam–plasma instabilities in the intergalactic medium are not suppressed but their counterparts in the solar wind can be suppressed as evidenced by propagating type-III solar radio bursts.

Forward Modeling of the Type III Radio Burst Exciter

In this work, we propose a forward-modeling method to study the trajectory and speed of the interplanetary (IP) Type-III radio burst exciter. The model assumes that the source of an IP Type-III radio burst moves outward from the Sun following the Parker spiral field line. Using the arrival time of the radio waves at multiple spacecraft, we are able to determine the trajectory of the radio source in the Ecliptic plane, and its outward speed, as well as the injection time and longitude of the associated electron beam near the solar surface that triggers the Type-III radio burst. For the application of this method, we design a system to gather the arrival time of the radio wave from the radio dynamic spectra observed by Solar Terrestrial Relations Observatory (STEREO)/WAVES and Wind/WAVES. Then the system forward models the trajectory and speed of the radio burst exciter iteratively according to an evaluation function. Finally, we present a survey of four Type-III radio bursts that are well discussed in the literature. The modeled trajectories of the radio source are consistent with the previous radio-triangulation results, the longitude of the associated active region, or the location of Langmuir waves excited by the electron beam.

On Solar Recurrent Coronal Jets: Coronal Geysers as Sources of Electron Beams and Interplanetary Type-III Radio Bursts

Abstract Coronal jets are transitory small-scale eruptions that are omnipresent in solar observations. Active regions jets produce significant perturbations on the ambient solar atmosphere and are believed to be generated by microflare reconnection. Multiple sets of recurrent jets are identified in extreme-ultraviolet filter imaging. In this work we analyze the long timescale recurrence of coronal jets originating from a unique footpoint structure observed in the lower corona. We report the detection of penumbral magnetic structures in the lower corona. These structures, which we call “coronal geysers,” persist through multiple reconnection events that trigger recurrent jets in a quasi-periodical trend. Recurrent jet eruptions have been associated with Type-III radio bursts that are manifestations of traveling non-thermal electron beams. We examine the assumed link, as the coronal sources of interplanetary Type-III bursts are still open for debate. We scrutinized the hypothesized association by temporally correlating a statistically significant sample of six Geyser structures that released at least 50 recurrent jets, with correspondent Type-III radio bursts detected in the interplanetary medium. Data analysis of these phenomena provides new information on small-scale reconnection, non-thermal electron beam acceleration, and energy release. We find that the penumbral Geyser-like flaring structures produce recurring jets. They can be long-lived, quasi-stable, and act as coronal sources for Type-III bursts, and, implicitly, upward accelerated electron beams.

3He-rich Solar Energetic Particles from Sunspot Jets

Abstract Solar sources of suprathermal (&lt;1 MeV nucleon−1) 3He-rich solar energetic particles (SEPs) have been commonly associated with jets originating in small, compact active regions at the periphery of near-equatorial coronal holes. Sources of relatively rare, high-energy (&gt;10 MeV nucleon−1) 3He-rich SEPs remain unexplored. Here we present two of the most intense 3He-rich (3He/4He &gt; 1) SEP events of the current solar cycle 24 measured on the Advanced Composition Explorer at energy &gt;10 MeV nucleon−1. Although 3He shows high intensities, Z &gt; 2 ions are below the detection threshold. The events are accompanied by type-III radio bursts, but no type-II emission as typically seen for suprathermal 3He-rich SEPs. The corresponding solar sources were analyzed using high-resolution, extreme-ultraviolet imaging and photospheric magnetic field observations on the Solar Dynamics Observatory. We find the sources of these events associated with jets originating at the boundary of large sunspots with complex βγδ magnetic configuration. Thus, details of the underlying photospheric field apparently are important to produce 3He to high energies in the examined events.

Tracking of an electron beam through the solar corona with LOFAR

The Sun’s activity leads to bursts of radio emission, among other phenomena. An example is type-III radio bursts. They occur frequently and appear as short-lived structures rapidly drifting from high to low frequencies in dynamic radio spectra. They are usually interpreted as signatures of beams of energetic electrons propagating along coronal magnetic field lines. Here we present novel interferometric LOFAR (LOw Frequency ARray) observations of three solar type-III radio bursts and their reverse bursts with high spectral, spatial, and temporal resolution. They are consistent with a propagation of the radio sources along the coronal magnetic field lines with nonuniform speed. Hence, the type-III radio bursts cannot be generated by a monoenergetic electron beam, but by an ensemble of energetic electrons with a spread distribution in velocity and energy. Additionally, the density profile along the propagation path is derived in the corona. It agrees well with three-fold coronal density model by (1961, ApJ, 133, 983).

3He-rich Solar Energetic Particles in Helical Jets on the Sun

Abstract Particle acceleration in stellar flares is ubiquitous in the universe; however, our Sun is the only astrophysical object where energetic particles and their source flares can both be observed. The acceleration mechanism in solar flares, tremendously enhancing (up to a factor of 10,000) rare elements like 3He and ultra-heavy nuclei, has been puzzling for almost 50 years. Here we present some of the most intense 3He- and Fe-rich solar energetic particle events ever reported. The events were accompanied by nonrelativistic electron events and type-III radio bursts. The corresponding high-resolution, extreme-ultraviolet imaging observations have revealed for the first time a helical structure in the source flare with a jet-like shape. The helical jets originated in relatively small, compact active regions, located at the coronal-hole boundary. A mini-filament at the base of the jet appears to trigger these events. The events were observed with the two Solar Terrestrial Relations Observatories on the backside of the Sun, during the period of increased solar activity in 2014. The helical jets may be a distinct feature of these intense events that is related to the production of high 3He and Fe enrichments.

PLASMA EMISSION BY COUNTER-STREAMING ELECTRON BEAMS

ABSTRACT The radiation emission mechanism responsible for both type-II and type-III solar radio bursts is commonly accepted as plasma emission. Recently Ganse et al. suggested that type-II radio bursts may be enhanced when the electron foreshock geometry of a coronal mass ejection contains a double hump structure. They reasoned that the counter-streaming electron beams that exist between the double shocks may enhance the nonlinear coalescence interaction, thereby giving rise to more efficient generation of radiation. Ganse et al. employed a particle-in-cell simulation to study such a scenario. The present paper revisits the same problem with EM weak turbulence theory, and show that the fundamental (F) emission is not greatly affected by the presence of counter-streaming beams, but the harmonic (H) emission becomes somewhat more effective when the two beams are present. The present finding is thus complementary to the work by Ganse et al.

A New Look at Type-III Bursts and Their Use as Coronal Diagnostics

We present meter wave solar radio spectra of the highest spectrotemporal resolution achieved to date. The observations, obtained with the first station of the Long Wavelength Array (LWA1), show unprecedented detail of solar emissions across a wide bandwidth during a Type III/IIIb storm. Our flux calibration demonstrates that the LWA1 can detect Type III bursts much weaker than 1 SFU, much lower than previous observations, and that the distribution of fluxes in these bursts varies with frequency. The high sensitivity and low noise in the data provide strong constraints to models of this type of plasma emission. The continuous generation of electron beams in the corona revealed by the high density Type III storm is evidence for ubiquitous magnetic reconnection in the lower corona. Such an abundance of reconnection events not only contributes to the total coronal energy budget, but also provides an engine by which to form the populations of seed particles responsible for proton-rich solar energetic particle events. An active region with such levels of reconnection and the accompanying type III/IIIb storms is here proposed to be associated with an increase of SEP production if a CME erupts. The data's constraints on existing theories of type IIIIb production are used to make an association of the observed type IIIb storm to specific electron beam paths with increased inhomogeneities in density, temperature, and or turbulence. This scenario ties in the observed timing of III and IIIb storms, constrained theories of type III and IIIb emission, and the ability of the emitting AR to produce a strong SEP event. The result requires but a single observable to cement these ideas, the statistical correlation of type III/IIIb activity with SEP-productive AR.

Whistler wave generation by non-gyrotropic, relativistic, electron beams

Particle-in-cell code, EPOCH, is used for studying features of the wave component evident to propagate backwards from the front of the non-gyrotropic, relativistic beam of electrons injected in the Maxwellian, magnetised background plasma with decreasing density profile. According to recent findings presented in Tsiklauri [Phys. Plasmas 18, 052903 (2011)], Schmitz and Tsiklauri [Phys. Plasmas 20, 062903 (2013)], and Pechhacker and Tsiklauri [Phys. Plasmas 19, 112903 (2012)], in a 1.5-dimensional magnetised plasma system, the non-gyrotropic beam generates freely escaping electromagnetic radiation with properties similar to the Type-III solar radio bursts. In this study, the backwards propagating wave component evident in the perpendicular components of the electromagnetic field in such a system is presented for the first time. Background magnetic field strength in the system is varied in order to prove that the backwards propagating wave's frequency, prescribed by the whistler wave dispersion relation, is proportional to the specified magnetic field. Moreover, the identified whistlers are shown to be generated by the normal Doppler-shifted relativistic resonance. Large fraction of the energy of the perpendicular electromagnetic field components is found to be carried away by the whistler waves, while a small but sufficient fraction is going into L- and R-electromagnetic modes.

A Statistical Analysis of the Type-III Bursts in Centimeter and Decimeter Wavebands

A statistical analysis of the type-III bursts observed by the spectrographs in the ranges of 625∼1500MHz, 2600-3800MHz, and 5200-7600 MHz during the 23rd solar cycle (from 2000 July to 2004 September) is carried out. The distribution of the type-III bursts, and their durations, frequency drift rates, polarization degrees and frequency bandwidths are given in this paper. The results indicate that the average values of the frequency drift rates and frequency bandwidths increase with the frequency. The average values of the durations and polarization degrees are neither constant nor uniformly varied over a broad frequency range. Most of type-III bursts are distributed in the range from 625 to 3800MHz, and decrease with the frequency in number. This analysis shows that the places of electron acceleration and energy release are mainly in the decimetric range, and the characteristic of this frequency range is possibly related with the magnetic configuration at the decimeter wavelengths, as well as the electron acceleration in the magnetic reconnection site close to the main flare. However, there are also a considerable number of type-III bursts in the range of 5200-7600MHz, it means that the sites of electron acceleration are widely distributed in the coronal region. The radiation mechanisms of type-III bursts at the centimeter-decimeter wavelengths include most probably the coherent plasma radiation and the emission process of electron cyclotron maser.

The 17 January 2005 Complex Solar Radio Event Associated with Interacting Fast Coronal Mass Ejections

On 17 January 2005 two fast coronal mass ejections were recorded in close succession during two distinct episodes of a 3B/X3.8 flare. Both were accompanied by metre-to-kilometre type-III groups tracing energetic electrons that escape into the interplanetary space and by decametre-to-hectometre type-II bursts attributed to CME-driven shock waves. A peculiar type-III burst group was observed below 600 kHz 1.5 hours after the second type-III group. It occurred without any simultaneous activity at higher frequencies, around the time when the two CMEs were expected to interact. We associate this emission with the interaction of the CMEs at heliocentric distances of about 25 R ⊙. Near-relativistic electrons observed by the EPAM experiment onboard ACE near 1 AU revealed successive particle releases that can be associated with the two flare/CME events and the low-frequency type-III burst at the time of CME interaction. We compare the pros and cons of shock acceleration and acceleration in the course of magnetic reconnection for the escaping electron beams revealed by the type-III bursts and for the electrons measured in situ.

CORONAL JETS, MAGNETIC TOPOLOGIES, AND THE PRODUCTION OF INTERPLANETARY ELECTRON STREAMS

We investigate the acceleration source of the impulsive solar energetic particle (SEP) events on 2007 January 24. Combining the in situ electron measurements and remote-sensing solar observations, as well as the calculated magnetic fields obtained from a potential-field source-surface model, we demonstrate that the jets associated with the hard X-ray flares and type-III radio bursts, rather than the slow and partial coronal mass ejections, are closely related to the production of interplanetary electron streams. The jets, originated from the well-connected active region (AR 10939) whose magnetic polarity structure favors the eruption, are observed to be forming in a coronal site, extending to a few solar radii, and having a good temporal correlation with the electron solar release. The open-field lines near the jet site are rooted in a negative polarity, along which energetic particles escape from the flaring AR to the near-Earth space, consistent with the in situ electron pitch angle distribution. The analysis enables us to propose a coronal magnetic topology relating the impulsive SEP events to their solar source.

SOLAR ENERGETIC PARTICLE 3 He-RICH EVENTS FROM THE NEARLY QUIET SUN IN 2007-2008

We have used Advanced Composition Explorer instruments to survey the period 2007 March through the end of 2008 for ^3He-rich solar energetic particle (SEP) events occurring during near solar minimum conditions. Four events were found, all associated with single solar active regions in the western hemisphere. They all show ^3He:^4He ratios of a few percent (i.e.,≳100 times solar system abundances), low intensities, and spectra extending up to at least 1 MeV nucleon^(–1). Two events, on 2008 February 4 and 2008 June 16, were devoid of signatures associated with ^3He-rich SEPs, namely they lacked associations with energetic electrons and type-III bursts. In addition, there were no clear coronal mass ejections and X-ray flare activity was very low or absent. We take this as evidence that the irreducible requirement for ^3He-rich SEPs is a western hemisphere solar active region where magnetic and plasma processes preferentially energize ^3He and heavy ions.