Whistlers in the solar corona and their relevance to fine structures of type IV radio emission

This event allows us to investigate how plasma–magnetic field interactions in the solar corona can produce suprathermal electron populations over periods from tens of minutes to several hours, and the interactions of wave-particle and wave-wave lead to characteristic fine structures of the emission. An intense and broad solar radio burst type IV was recorded by CALLISTO spectrometer from 240-360 MHz. Using data from a the KRIM observatory, we aim to provide a comprehensive description of the synopsis formation and dynamics of a a single solar burst type IV event due to active region AR2222. For five minutes, the event exhibited strong pulsations on various time scales and “broad patterns” with a formation of a group type III solar burst. AR 2222 remained the most active region, producing a number of minor C-Class solar flares. The speed of the solar wind also exceeds 370.8 km/second with 10.2 g/cm3 density of proton in the solar corona. The radio flux also shows 171 SFU. Besides, there are 3 active regions, AR2217, AR2219 and AR2222 potentially pose a threat for M-class solar flares. Active region AR2222 have unstable 'beta-gamma' magnetic fields that harbor energy for M-class flares. As a conclusion, we believed that Sun’s activities more active in order to achieve solar maximum cycle at the end of 2014.

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Strongly structured radio emission observed by LOFAR on August 25, 2014

10.5194/egusphere-egu2020-14784 ◽

2020 ◽

Author(s):

Jasmina Magdalenic ◽

Christophe Marque ◽

Richard Fallows ◽

Gottfried Mann ◽

Christian Vocks ◽

...

Keyword(s):

Radio Emission ◽

Electron Beams ◽

Low Frequency ◽

Impulsive Phase ◽

Continuum Emission ◽

Type Ii ◽

Type Iii ◽

Type Iv ◽

Fine Structures ◽

Radio Event

<p>On August 25, 2014, NOAA AR 2146 produced the M2.0 class flare (peaked at 15:11 UT). The flare was associated with a halo CME and a radio event observed by LOFAR (the LOw-Frequency Array). The radio event consisted of a type II, type III and type IV radio emissions. In this study, we present LOFAR observations of the type II (radio signatures of shock waves) and type III bursts (radio signatures of fast electron beams propagating along open or quasi open field lines). &#160;Both, the type II burst and type III bursts show strong fragmentation of the radio emission. Although fine structures of type II bursts were already reported, the richness of the fine structures observed in the studied event is unprecedented. We found type II fine structures morphologically very similar to the ones sometimes seen superposed on type IV continuum emission, and similar to simple narrowband super short structures (Magdalenic et al., 2006). The group of type III bursts was as usually, observed during the impulsive phase of the flare. The high frequency/time resolution LOFAR observations reveal that only few of the observed type III bursts have a smooth emission profile, and the majority of bursts is strongly fragmented. Surprisingly, fine structures of some type III bursts show similarities to the fine structures observed in the type II burst, but on a smaller frequency scale. Some of the type III bursts show a non-organized patchy structure which gives an indication on the possibly related turbulence processes. We show that these LOFAR observations bring completely new insight and pose a new challenge for the physics of the acceleration of electron beams and associated emission processes.</p>

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Theory of Type IV dm Bursts

Symposium - International Astronomical Union ◽

10.1017/s0074180900037098 ◽

1980 ◽

Vol 86 ◽

pp. 341-361 ◽

Cited By ~ 1

Author(s):

Jan Kuijpers

Keyword(s):

Fine Structure ◽

Radio Emission ◽

Radio Sources ◽

The Sun ◽

Type Iv ◽

Fine Structures ◽

Continuum Radio ◽

Radio Flare

The study of fine structures in continuum radio emission from the sun is important to probe the physics of radio sources and of flares in particular. In this light the existing fine structure theories are reviewed and an application to a radio flare is given.

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LOFAR observations of the quiet solar corona

Astronomy and Astrophysics ◽

10.1051/0004-6361/201630067 ◽

2018 ◽

Vol 614 ◽

pp. A54 ◽

Cited By ~ 9

Author(s):

C. Vocks ◽

G. Mann ◽

F. Breitling ◽

M. M. Bisi ◽

B. Dąbrowski ◽

...

Keyword(s):

Radio Emission ◽

Solar Corona ◽

Density Profile ◽

Extreme Ultraviolet ◽

Low Frequency ◽

Scale Height ◽

Solar Radio Emission ◽

Radial Magnetic Field ◽

Brightness Temperatures ◽

Hydrostatic Model

Context. The quiet solar corona emits meter-wave thermal bremsstrahlung. Coronal radio emission can only propagate above that radius, Rω, where the local plasma frequency equals the observing frequency. The radio interferometer LOw Frequency ARray (LOFAR) observes in its low band (10–90 MHz) solar radio emission originating from the middle and upper corona. Aims. We present the first solar aperture synthesis imaging observations in the low band of LOFAR in 12 frequencies each separated by 5 MHz. From each of these radio maps we infer Rω, and a scale height temperature, T. These results can be combined into coronal density and temperature profiles. Methods. We derived radial intensity profiles from the radio images. We focus on polar directions with simpler, radial magnetic field structure. Intensity profiles were modeled by ray-tracing simulations, following wave paths through the refractive solar corona, and including free-free emission and absorption. We fitted model profiles to observations with Rω and T as fitting parameters. Results. In the low corona, Rω < 1.5 solar radii, we find high scale height temperatures up to 2.2 × 106 K, much more than the brightness temperatures usually found there. But if all Rω values are combined into a density profile, this profile can be fitted by a hydrostatic model with the same temperature, thereby confirming this with two independent methods. The density profile deviates from the hydrostatic model above 1.5 solar radii, indicating the transition into the solar wind. Conclusions. These results demonstrate what information can be gleaned from solar low-frequency radio images. The scale height temperatures we find are not only higher than brightness temperatures, but also than temperatures derived from coronograph or extreme ultraviolet (EUV) data. Future observations will provide continuous frequency coverage. This continuous coverage eliminates the need for local hydrostatic density models in the data analysis and enables the analysis of more complex coronal structures such as those with closed magnetic fields.

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EXPLORATION OF THE SOLAR DECAMETER RADIO EMISSION WITH THE UTR-2 RADIO TELESCOPE

Radio physics and radio astronomy ◽

10.15407/rpra26.01.074 ◽

2021 ◽

Vol 26 (1) ◽

pp. 74-89

Author(s):

V. N Melnik ◽

◽

A. A. Konovalenko ◽

V. V. Dorovskyy ◽

A. Lecacheux ◽

...

Keyword(s):

Radio Emission ◽

Radio Telescope ◽

Solar Radio Emission ◽

The Sun ◽

Type Ii ◽

Time Frequency ◽

Type Iii ◽

Type Iv ◽

Decameter Radio ◽

Type Ii Bursts

Purpose: The overview of the scientifi c papers devoted to the study of the solar decameter radio emission with the world’s largest UTR-2 radio telescope (Ukraine) published for the last 50 years. Design/methodology/approach: The study and analysis of the scientifi c papers on both sporadic and quiet (thermal) radiation of the Sun recorded with the UTR-2 radio telescope at the decameter wavelength range. Findings: The most signifi cant observational and theoretical results of the solar radio emission studies obtained at the Institute of Radio Astronomy of the National Academy of Sciences of Ukraine for the last 50 years are given. Conclusions: For the fi rst time, at frequencies below 30 MHz, the Type II bursts, Type IV bursts, S-bursts, drift pairs and spikes have been recorded. The dependences of these bursts parameters on frequency within the frequency band of 9 to 30 MHz were obtained. The models of their generation and propagation were suggested. Moreover, for the fi rst time the fi ne time-frequency structures of the Type III bursts, Type II bursts, Type IV bursts, U- and J-bursts, S-bursts, and drift pairs have been observed due to the high sensitivity and high time-frequency resolutions of the UTR-2 radio telescope. The super-fi ne structure of Type II bursts with a “herringbone” structure was identifi ed, which has never been observed before. New types of bursts were discovered: “caterpillar” bursts, “dog-leg” bursts, Type III bursts with decay, Type III bursts with changing drift rate sign, Type III-like bursts, Jb- and Ub-bursts, etc. An interpretation of the unusually high drift rates and drift rates with alternating signs of the Type III-like bursts was suggested. Based on the dependence of spike durations on frequency, the coronal plasma temperature profi le at the heliocentric heights of 1.5–3RS was determined. Usage of the heliographic and interferometric methods gave the possibility to start studies of the spatial characteristics – sizes and locations of the bursts emission sources. Thus, it was shown that at the decameter band, the Type III burst durations were defi ned by the emission source linear sizes, whereas the spike durations were governed by the collision times in the source plasma. It was experimentally proved that the effective brightness temperatures of the sources of solar sporadic radio emission at the decameter band may reach values of 1014–1015 K. In addition, it was found that the radii of the quiet Sun at frequencies 20 and 25 MHz are close to the distances from the Sun at which the local plasma frequency is equal to the corresponding observed frequency of radio emission in the Baumbach–Allen model. Key words: UTR-2; Sun; decameter radio emission; radio bursts; corona

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Metric observations of transient, quasi-periodic radio emission from the solar corona in association with a “halo” CME and an “EIT wave” event

Astronomy and Astrophysics ◽

10.1051/0004-6361:20030019 ◽

2003 ◽

Vol 400 (2) ◽

pp. 753-758 ◽

Cited By ~ 23

Author(s):

R. Ramesh ◽

C. Kathiravan ◽

A. Satya Narayanan ◽

E. Ebenezer

Keyword(s):

Radio Emission ◽

Solar Corona ◽

Wave Event

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Type I Radio Emission and the Structure of the Solar Corona Results of the Stereo-I Experiment

Radio Physics of the Sun ◽

10.1007/978-94-010-9722-2_57 ◽

1980 ◽

pp. 401-404

Author(s):

J. L. Bougeret ◽

J. L. Steinberg

Keyword(s):

Radio Emission ◽

Solar Corona ◽

Type I

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Summary of the Discussion on Type IV Radio Emission

The Solar Corona ◽

10.1016/b978-1-4832-2872-3.50043-7 ◽

1963 ◽

pp. 292-295

Author(s):

A.D. FOKKER

Keyword(s):

Radio Emission ◽

Type Iv

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Comparative analysis of solar radio bursts before and during CME propagation

Astronomy and Astrophysics ◽

10.1051/0004-6361/201629489 ◽

2019 ◽

Vol 625 ◽

pp. A63 ◽

Cited By ~ 1

Author(s):

G. Dididze ◽

B. M. Shergelashvili ◽

V. N. Melnik ◽

V. V. Dorovskyy ◽

A. I. Brazhenko ◽

...

Keyword(s):

Comparative Analysis ◽

Radio Emission ◽

Instantaneous Frequency ◽

Narrow Band ◽

Radio Bursts ◽

Frequency Bandwidth ◽

Plasma Parameters ◽

Type Iii ◽

Type Iv ◽

Band Type

Context. As is well known, coronal mass ejection (CME) propagation often results in the fragmentation of the solar atmosphere on smaller regions of density (magnetic field) enhancement (depletion). It is expected that this type of fragmentation may have radio signatures. Aims. The general aim of the present paper is to perform a comparative analysis of type III solar and narrow-band type-III-like radio burst properties before and during CME events, respectively. The main goal is to analyze radio observational signatures of the dynamical processes in solar corona. In particular, we aim to perform a comparison of local plasma parameters without and with CME propagation, based on the analysis of decameter radio emission data. Methods. In order to examine this intuitive expectation, we performed a comparison of usual type III bursts before the CME with narrow-band type-III-like bursts, which are observationally detectable on top of the background type IV radio bursts associated with CME propagation. We focused on the analysis of in total 429 type III and 129 narrow-band type-III-like bursts. We studied their main characteristic parameters such as frequency drift rate, duration, and instantaneous frequency bandwidth using standard statistical methods. Furthermore, we inferred local plasma parameters (e.g., density scale height, emission source radial sizes) using known definitions of frequency drift, duration, and instantaneous frequency bandwidth. Results. The analysis reveals that the physical parameters of coronal plasma before CMEs considerably differ from those during the propagation of CMEs (the observational periods 2 and 4 with type IV radio bursts associated with CMEs). Local density radial profiles and the characteristic spatial scales of radio emission sources vary with radial distance more drastically during the CME propagation compared to the cases of quasistatic solar atmosphere without CME(s) (observational periods 1 and 3). Conclusions. The results of the work enable us to distinguish different regimes of plasma state in the solar corona. Our results create a solid perspective from which to develop novel tools for coronal plasma studies using radio dynamic spectra.

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