Type IIIb Bursts Research Articles

An Interplanetary Type IIIb Radio Burst Observed by Parker Solar Probe and Its Emission Mechanism

Abstract Type IIIb radio bursts were identified as a chain of quasi-periodic striae in dynamic spectra, drifting from high to low frequencies in a manner similar to type III bursts, which fine structures may provide a clue to a better understanding of emission mechanisms. The approaching observation of the Parker Solar Probe (PSP) spacecraft provides a new chance of probing type IIIb bursts in the vicinity of the Sun. In this Letter, combining the in situ measurement of PSP and the empirical model of solar atmospheres in open magnetic field regions, we analyze in detail a typical event of interplanetary (IP) type IIIb bursts observed by PSP, which was first reported by Pulupa et al. Our results show that the electron cyclotron maser (ECM) emission can probably play an important role in the excitation mechanism of the IP type IIIb burst and the formation of the fine striae structure may be attributed to the modulation of Alfvén waves on the growth rate of the ECM instability.

Properties of Type III and Type IIIb Bursts in the Frequency Band of 8 – 80 MHz During PSP Perihelion at the Beginning of April 2019

Properties of type III and type IIIb bursts in the frequency band of 8-80 MHz observed by the radio telescopes Ukrainian Radio Interferometer of NASU-2 (URAN-2) (Poltava) and Giant Ukrainian Radio Telescope (GURT) (Kharkiv) during the Parker Solar Probe (PSP) perihelion in April 2019 are discussed. These correspond of those that were observed by PSP at frequencies <19 MHz. We analyze dependences of drift rates and durations on frequency for these bursts. We show that drift rate dependences on frequency agree well with those derived from the Newkirk corona if source velocities are between 0.17 and 0.2 c for both type IIIb bursts and type III bursts under the assumption that the first ones are fundamentals and the second ones are their harmonics. However, all observational dependences are flatter in comparison with the dependences for a Newkirk corona. We assume that this can be related with coronal temperature decreasing at heliocentric distances from 1.35 to 6.5 solar radii. Duration dependencies of type IIIb and type III bursts on frequency in the range of 10-70 MHz are also obtained. We note that the durations and drift rates of type III bursts as well as their dependences on frequency differ essentially from those for type IIIb bursts.

LOFAR Observations of Fine Spectral Structure Dynamics in Type IIIb Radio Bursts

Solar radio emission features a large number of fine structures demonstrating great variability in frequency and time. We present spatially resolved spectral radio observations of type IIIb bursts in the $30-80$ MHz range made by the Low Frequency Array (LOFAR). The bursts show well-defined fine frequency structuring called "stria" bursts. The spatial characteristics of the stria sources are determined by the propagation effects of radio waves; their movement and expansion speeds are in the range of 0.1-0.6c. Analysis of the dynamic spectra reveals that both the spectral bandwidth and the frequency drift rate of the striae increase with an increase of their central frequency; the striae bandwidths are in the range of ~20-100 kHz and the striae drift rates vary from zero to ~0.3 MHz s^-1. The observed spectral characteristics of the stria bursts are consistent with the model involving modulation of the type III burst emission mechanism by small-amplitude fluctuations of the plasma density along the electron beam path. We estimate that the relative amplitude of the density fluctuations is of dn/n~10^-3, their characteristic length scale is less than 1000 km, and the characteristic propagation speed is in the range of 400-800 km/s. These parameters indicate that the observed fine spectral structures could be produced by propagating magnetohydrodynamic waves.

Properties of Decameter IIIb–III Pairs

A large number of Type IIIb-III pairs, in which the first component is a Type IIIb burst and the second one is a Type III burst, are often recorded during decameter Type III burst storms. From the beginning of their observation, the question of whether the components of these pairs are the first and the second harmonics of radio emission or not has remained open. We discuss properties of decameter IIIb-III pairs in detail to answer this question. The components of these pairs, Type IIIb bursts and Type III bursts, have essentially different durations and polarizations. At the same time their frequency drift rates are rather close, provided that the drift rates of Type IIIb bursts are a little larger those of Type III bursts at the same frequency. Frequency ratios of the bursts at the same moment are close to two. This points at a harmonic connection of the components in IIIb-III pairs. At the same time there was a serious difficulty, namely why the first harmonic had fine frequency structure in the form of striae and the second harmonic did not have it. Recently Loi, Cairns, and Li ( Astrophys. J. 790, 67, 2014) succeeded in solving this problem. The physical aspects of observational properties of decameter IIIb-III pairs are discussed and pros and cons of harmonic character of Type IIIb bursts and Type III bursts in IIIb-III pairs are presented. We conclude that practically all properties of the IIIb-III pair components can be understood in the framework of the harmonic relation of the components of the IIIb-III pairs.

The Storm of Decameter Spikes During the Event of 14 June 2012

An event on 14 June 2012, observed with the radio telescopes UTR-2 (Kharkov, Ukraine), URAN-2 (Poltava, Ukraine), and NDA (Nancay, France) during a joint Summer campaign, is analyzed and discussed. The high solar activity resulted in a storm of spikes, and a storm of Type III bursts, Type IIIb bursts, and a Type IV burst observed in the decameter band. During the observed time interval, the average flux of radio emission changed twice. Using spikes as a tool for diagnostics of plasma parameters, we followed variations of the coronal temperature and the coronal magnetic field in the observed time interval. Thus, in frames of the model described in this article the observed decameter spikes’ durations of 0.3 – 1 seconds correspond to the coronal plasma temperatures of ${\approx}\, 0.1\,\mbox{--}\,0.6 \times10^{6}~\mbox{K}$ . At the same time the spikes’ frequency bandwidths of 25 – 80 kHz give us the magnetic-field value of about 2 G.

A SCENARIO FOR THE FINE STRUCTURES OF SOLAR TYPE IIIb RADIO BURSTS BASED ON ELECTRON CYCLOTRON MASER EMISSION

A scenario based on the electron cyclotron maser emission is proposed for the fine structures of solar radio emission in the present discussion. It is suggested that under certain conditions modulation of the ratio between the plasma frequency and electron gyro-frequency by ultra low frequency waves, which is a key parameter for excitation of the electron cyclotron maser instability, may lead to the intermittent emission of radio waves. As an example, the explanation of the observed fine-structure components in the solar type IIIb burst is discussed in detail. Three primary issues of the type IIIb bursts are addressed: 1) what is the physical mechanism that results in the intermittent emission elements that form a chain in the dynamic spectrum of type IIIb bursts, 2) what causes the split pair (or double stria) and the triple stria, 3) why in the events of fundamental-harmonic pair emission there is only IIIb-III, but IIIb-IIIb or III-IIIb cases are very rarely observed.

PRODUCTION OF FINE STRUCTURES IN TYPE III SOLAR RADIO BURSTS DUE TO TURBULENT DENSITY PROFILES

Magnetic reconnection events in the corona release energetic electron beams along open field lines, and the beams generate radio emission at multiples of the electron plasma frequency f{sub p} to produce type III solar radio bursts. Type III bursts often exhibit irregularities in the form of flux modulations with frequency and/or local temporal advances and delays, and a type IIIb burst represents the extreme case where a type III burst is fragmented into a chain of narrowband features called striae. Remote and in situ spacecraft measurements have shown that density turbulence is ubiquitous in the corona and solar wind, and often exhibits a Kolmogorov power spectrum. In this work, we numerically investigate the effects of one-dimensional macroscopic density turbulence (along the beam direction) on the behavior of type III bursts, and find that this turbulence produces stria-like fine structures in the dynamic spectra of both f{sub p} and 2 f{sub p} radiation. Spectral and temporal fine structures in the predicted type III emission are produced by variations in the scattering path lengths and group speeds of radio emission, and in the locations and sizes of emitting volumes. Moderate turbulence levels yield flux enhancements with much broader half-power bandwidths in f{submore » p} than 2 f{sub p} emission, possibly explaining the often observed type IIIb-III harmonic pairs as being where intensifications in 2 f{sub p} radiation are not resolved observationally. Larger turbulence levels producing trough-peak regions in the plasma density profile may lead to broader, resolvable intensifications in 2 f{sub p} radiation, which may account for the type IIIb-IIIb pairs that are sometimes observed.« less

EFFECTS OF SPATIAL VARIATIONS IN CORONAL TEMPERATURES ON TYPE III BURSTS. I. VARIATIONS IN ELECTRON TEMPERATURE

The electron temperature Te and ion temperature Ti in the corona vary with time and location, due to transient and persistent activity on the Sun. A method is developed for incorporating spatial variations of coronal temperatures into our previous simulation model for coronal type III bursts. The effects on type III bursts are simulated here for monotonic Te variations and/or for spatially localized disturbances in Te . Localized Te disturbances are found to have stronger effects than monotonic variations. In the presence of localized Te disturbances, the dynamic spectra of fp and 2fp emission are modulated at frequencies corresponding to the disturbances, showing intense fine structures that are narrow band and slowly drifting. The fp emission may be observable although still significantly weaker and more patchy than the 2fp emission. Distinct signatures of Te disturbances are found in the dependence on frequency of the 2fp spectral characteristics, e.g., the maximum flux. In the presence of monotonically varying Te , the frequency drift rate for 2fp emission agrees quantitatively with an extended version of the standard prediction, depending on the plasma density profile and a characteristic, non-constant beam speed, which varies with position via dependence on Te , and agrees quantitatively with the simulated beam dynamics. The results thus indicate that nonthermal type III bursts offer a new tool to probe both spatially localized Te structures and monotonic Te variations in the corona. The presence of localized Te disturbances may be responsible for some fine structures in type IIIs, e.g., the flux modulations in type IIIb bursts.

EFFECTS OF SPATIAL VARIATIONS IN CORONAL ELECTRON AND ION TEMPERATURES ON TYPE III BURSTS. II. VARIATIONS IN ION TEMPERATURE

Quasilinear-based simulations are presented for the effects on coronal type III bursts of spatially varying ion temperature Ti in the corona. The simulations use a newly developed method for integrating spatial variations of coronal temperatures into our previous simulations for constant temperatures. The effects are simulated for monotonic Ti variations and/or for spatially localized enhancements in Ti . Generally, a localized enhancement in Ti has stronger effects on type III bursts than a corresponding monotonic variation in Ti . A localized Ti enhancement causes modulations to the dynamic spectra of fp and 2fp emission at frequencies corresponding to the disturbance: a narrowband slowly drifting intensification for both fp and 2fp emission and a narrowband suppression for 2fp emission. The fp emission may become observable due to the disturbance, although still much weaker than the 2fp emission. Signatures of the Ti enhancement are found in the 2fp spectral characteristics, e.g., the maximum flux and frequency drift rate. Importantly, these signatures are distinct from those of localized disturbances in electron temperature Te . The results indicate that coronal type III bursts provide a new tool to probe and distinguish localized disturbances in Ti or Te in the corona. Additionally, the presence of multiple spatially confined Ti enhancements at different heights may produce some observed fine structures in type III bursts; e.g., stria bursts and associated flux modulations in type IIIb bursts, and flux modulations in type IIIs whose beams traverse coronal shocks.

Imprints of coronal temperature disturbances on type III bursts

The electron temperature Te and ion temperature Ti in the corona vary with time and location, due to transient and persistent activity on the Sun. The effects of spatially localized disturbances in Te and Ti on coronal type III radio bursts are simulated. The disturbances are superimposed on monotonically varying temperature backgrounds and arise from spatially confined solar activity, Qualitatively and quantitatively different imprints are found on the curve of the maximum flux versus frequency of type III bursts, because of the disturbances in Te and Ti. The results indicate that nonthermal coronal type III bursts offer a new tool to probe and distinguish between spatially localized structures of Te and Ti along the paths of type III beams. Furthermore, localized temperature disturbances may be responsible for some fine structures in type III bursts, e.g., striae in type IIIb bursts in the presence of multiple, localized temperature disturbances.

Sporadic radio emission of the Sun in the decametre range

AbstractResults of the last observations of solar sporadic radio emission at the UTR-2 radio telescope (Kharkov, Ukraine) at the frequencies 10 - 30 MHz are presented. The use of new backend facilities, the DSP and 60-channel spectrometer, allows us to obtain data with time resolution up to 2 ms and frequency resolution of 12 kHz in the continuous frequency band 12 MHz. Usual Type III bursts, Type IIIb bursts, U- and J-bursts in the decameter range are discussed. Special attention is paid to detection and analysis of Type II bursts and their properties, newly discovered fine time structures of Type III bursts, Type III-like bursts, s-bursts, new observational features of drift pair bursts, and ‘absorption’ bursts.

Solar sporadic radio emission in the decametre waveband

The first results of observations of solar sporadic radio emission with the UTR-2 radio telescope in 2001–2003 are reported in this paper. Using new back-end facilities, the digital spectro-polarimeter and 60-channel spectrometer allowed us to obtain data with a time resolution up to 2 ms and a frequency resolution of 12 kHz in a continuous frequency band of 12 MHz. The usual type III bursts, type IIIb bursts, U and J bursts, spikes and unusual bursts in the decametre wavelength band are discussed in this paper. Special attention is paid to the detection and analysis of type II bursts and their properties, the fine structure of type III bursts, the new observational features of drift pair bursts, ‘absorption’ bursts and the statistical analysis of solar radio bursts.

On the solar type III radio burst emission process

view Abstract Citations (12) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the solar type III radio burst emission process Wentzel, D. G. Abstract The application of a version of the nonlinear plasma theories involving plasma solitons to the corona is investigated. A fairly compact beam is assumed in order to initiate nonlinear plasma phenomena in the corona. The beam's survival is favored by open magnetic fields, and the solitons occur in a front about 1 km thick. The fundamental is emitted at this front and depends strongly on the beam energy through its dependence on the narrow angle of emission. The variability of the fundamental indicates the beam evolution at the beam's front. Observations addressed by the theory include correlations of type III bursts with coronal structure and temperature, the emission of fundamental and harmonic from different source volumes, the polarization of the fundamental, and the starting and disappearance of bursts in the corona, especially type IIIb bursts. Publication: The Astrophysical Journal Pub Date: May 1982 DOI: 10.1086/159905 Bibcode: 1982ApJ...256..271W Keywords: Electron Beams; Plasma Waves; Solar Corona; Solitary Waves; Type 3 Bursts; Harmonic Radiation; Magnetohydrodynamic Waves; Nonlinearity; Polarization (Waves); Solar Electrons; Solar Temperature; Solar Physics full text sources ADS |

Observations of the Structure of Type IIIb Radio Bursts

We observed short duration, narrow band Type IIIb radio bursts that occur just before the onset of a normal Type III burst. These observations were made with a multichannel radiometer with a center frequency of 25 MHz, time constant of 10 milliseconds and frequency resolution of 100 KHz. The average half power duration of a typical element of a Type III burst was determined. It was found to be very similar to the time profile of a normal Type III burst, i.e., sharp rise and exponential type decay. The duration of the exciter, tE, and the decay time constant, τ, determined from the average time profile were 0.88 and 0.31 seconds, respectively. The corresponding quantities for the associated Type III bursts are 6.0 and 2.1 seconds, respectively. It is interesting to note that the ratios are the same, and equal to 0.98. We found that there is no difference between the time profile of a Type III burst associated with a Type IIIb burst and that of an isolated Type III burst. We also found that the two quantities ‘tE’ and ‘ τ ’ are positively correlated in the case of isolated Type III bursts. The linear correlation coefficient is 0.70. This correlation seems to break down in the case of Type III bursts associated with Type IIIb bursts. We looked for a relation between durations of the elements of the Type IIIb bursts and that of the associated Type III bursts, and found that the two quantities are positively correlated. Lastly, we would like to point out that the elements of Type IIIb bursts observed by us are more intense than the associated Type III burst.

Collisionless deceleration of fast electron streams in the solar coronal plasma

The collisionless deceleration of electron streams responsible for type IIIb bursts has been investigated. For this the difference between the mean velocities of electron streams at plasma levels corresponding to 25 and 12.5 MHz, on one hand, at 12.5 and 6.25 MHz, on the other hand, is estimated. The mean velocity of electron streams between these levels is determined by the time delay in the moments of arrival of radio bursts from these levels. The distance between plasma levels is determined under the assumption that the (statistical) mean velocity of sources of the diffusive type III bursts is constant and equal toc/3 at all considered levels of the solar corona.

Theory of type IIIb solar radio bursts

During the initial space-time evolution of an electron beam injected into the corona, the strong beam-plasma interaction occurs at the head of the beam, leading to the amplification of a quasi-monochromatic large-amplitude plasma wave that stabilizes by trapping the beam particles. Oscillation of the trapped particles in the wave troughs amplifies sideband electrostatic waves. The sidebands and the main wave subsequently decay to observable transverse electromagnetic waves through the parametric decay instability. This process gives rise to the elementary striation bursts. Owing to velocity dispersion in the beam and the density gradient of the corona, the entire process may repeat at a finite number of discrete plasma levels, producing chains of elementary bursts. All the properties of the type IIIb bursts are accounted for in the context of the theory.

Scattering in the radiation source and the fundamental-harmonic hypothesis

A model for the radiation source for type III solar radio bursts which includes random density fluctuations is reviewed. This methodology is applied to the burst of 28 September, 1973, 03:19 UT which is an archetype ‘fundamental-harmonic’ pair. It is found that for scattering inhomogeneities consistent with those necessary to explain the observed sizes of the sources, it is impossible to amplify fundamental radiation in a source with a spatially uniform energy density in plasma waves; i.e., it is impossible to interpret this burst as a ‘fundamental-harmonic’ pair from such a source. However, the supposed ‘fundamental’ has fine structure similar to type IIIb bursts and since it is very difficult to explain these features except as fundamental radiation, it is concluded that there must be small clumps of intense plasma waves in the source which allow the fundamental to be amplified. These results are also applied to the hectometric burst of 19 July, 1971 for which a steep rise in brightness is observed between 10 and 50 R0. It is argued that the most plausible explanation of this rise is that the density inhomogeneities become sufficiently weak to allow the fundamental to be amplified in this range.

Type IIIb radio bursts: 80 MHz source position and theoretical model

We present Culgoora spectrograph and radioheliograph observations as well as a model of type IIIb bursts; the latter are defined as chains of striae of slow or no frequency drift, the chain as a whole drifting like a normal type III burst.

On the probability of occurrence of the type IIIb burst as a precursor

It is shown that a precursor type IIIb burst is really associated with a type III burst. The broad longitude distribution of occurrence of type IIIb bursts also suggests that these bursts are emitted at a large angle to the open magnetic field in the corona.