Fine Structure of Metric Type IV Radio Bursts Observed with the ARTEMIS-IV Radio-Spectrograph: Association with Flares and Coronal Mass Ejections

Bouratzis, C.; Hillaris, A.; Alissandrakis, C. E.; Preka‐Papadema, P.; Moussas, X.; Caroubalos, C.; Tsitsipis, P.; Kontogeorgos, A.

doi:10.1007/s11207-014-0562-2

Cited by 25 publications

(53 citation statements)

References 46 publications

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“…They exhibit high brightness temperature, T B ∼ 10 15 K in decimetric wavelengths (Benz 1986). In a recent work (Bouratzis et al 2015), we found a very good temporal association between energy release episodes and spikes. We used the time of first impulsive energy release, shown A&A 586, A29 (2016) by the first HXR/microwave peak, as the reference for timing the appearance of fine structures with respect to the evolution of the flare process.…”

Section: Introductionsupporting

confidence: 59%

High resolution observations with Artemis-IV and the NRH

Bouratzis

Hillaris

Alissandrakis

et al. 2016

A&A

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Context. Narrow-band bursts appear on dynamic spectra from microwave to decametric frequencies as fine structures with very small duration and bandwidth. They are believed to be manifestations of small scale energy release through magnetic reconnection. Aims. We analyzed 27 metric type IV events with embedded narrow-band bursts, which were observed by the ARTEMIS-IV radio spectrograph from 30 June 1999 to 1 August 2010. We examined the morphological characteristics of isolated narrow-band structures (mostly spikes) and groups or chains of structures. Methods. The events were recorded with the SAO high resolution (10 ms cadence) receiver of ARTEMIS-IV in the 270-450 MHz range. We measured the duration, spectral width, and frequency drift of ∼12 000 individual narrow-band bursts, groups, and chains. Spike sources were imaged with the Nançay radioheliograph (NRH) for the event of 21 April 2003. Results. The mean duration of individual bursts at fixed frequency was ∼100 ms, while the instantaneous relative bandwidth was ∼2%. Some bursts had measurable frequency drift, either positive or negative. Quite often spikes appeared in chains, which were closely spaced in time (column chains) or in frequency (row chains). Column chains had frequency drifts similar to type-IIId bursts, while most of the row chains exhibited negative frequently drifts with a rate close to that of fiber bursts. From the analysis of NRH data, we found that spikes were superimposed on a larger, slowly varying, background component. They were polarized in the same sense as the background source, with a slightly higher degree of polarization of ∼65%, and their size was about 60% of their size in total intensity. Conclusions. The duration and bandwidth distributions did not show any clear separation in groups. Some chains tended to assume the form of zebra, lace stripes, fiber bursts, or bursts of the type-III family, suggesting that such bursts might be resolved in spikes when viewed with high resolution. The NRH data indicate that the spikes are not fluctuations of the background, but represent additional emission such as what would be expected from small-scale reconnection.

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Section: Introductionsupporting

confidence: 59%

High resolution observations with Artemis-IV and the NRH

Bouratzis

Hillaris

Alissandrakis

et al. 2016

A&A

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“…ARTEMIS data were presented by Caroubalos et al (2001b); see also Fig. 17 of Bouratzis et al (2015). It was a complex event that occurred in active region 9077 and was associated to an X5.7 flare, starting at 10:03 UT near the center of the disk, and to a halo coronal mass ejection (CME).…”

Section: Overview Of the Event Of July 14 2000mentioning

confidence: 99%

“…The continuum was rich in embedded pulsations, spikes, fibers, and zebra patterns. Fiber bursts appeared around 10:33 UT and lasted until about 11:25 (Table 2 of Bouratzis et al 2015), often mixed with pulsations and other broadband structures (see Figs. 6−7 in Caroubalos et al 2001b).…”

Section: Overview Of the Event Of July 14 2000mentioning

confidence: 99%

High-resolution observations with ARTEMIS-JLS and the NRH

Alissandrakis

Bouratzis

Hillaris

2019

A&A

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Aims. We study the characteristics of intermediate drift bursts (fibers) embedded in a large type-IV event. Methods. We used high-sensitivity, low-noise dynamic spectra obtained with the acousto-optic analyzer (SAO) of the ARTEMIS-JLS solar radiospectrograph, in conjunction with high time-resolution images from the Nançay radioheliograph (NRH) and extreme ultraviolet (EUV) images from the Transition Region and Coronal Explorer (TRACE) to study fiber bursts during the large solar event of July 14, 2000. We computed both 2D and 1D images and applied high pass time filtering to the images and the dynamic spectrum in order to enhance the fiber-associated emission. For the study of the background continuum emission we used images averaged over several seconds. Results. Practically all fibers visible in the SAO dynamic spectra are identifiable in the NRH images. Fibers were first detected after the primary energy release in a moving type-IV event, probably associated with the rapid eastward expansion of the flare and the post-flare loop arcade. We found that fibers appeared as a modulation of the continuum intensity with a root mean square value of the order of 10%. Both the fibers and the continuum were strongly circularly polarized in the ordinary mode sense, indicating plasma emission at the fundamental. We detected a number of discrete fiber emission sources along two parallel stripes of ∼300 Mm in length, apparently segments of large-scale loops encompassing both the EUV loops and the CME-associated flux rope. We found cases of multiple fiber emissions appearing at slightly different positions and times; their consecutive appearance can give the impression of apparent motion with supra-luminal velocities. Images of individual fibers were very similar at 432.0 and 327.0 MHz. From the position shift of the sources and the time delays at low and high frequencies, we estimated the exciter speed and the frequency scale length along the loops for a well-observed group of fibers; we obtained consistent values from imaging and spectral data, supporting the whistler origin of the fiber emission. Finally we found that fibers in emission and fibers in absorption are very similar, confirming that they are manifestations of the same wave train.

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“…A catalog of metric type IV radio bursts observed with the ARTEMIS-IV solar radio spectrograph was compiled by Bouratzis et al (2015). As type IV bursts can be associated with both flare emissions and coronal mass ejection (CME) events, they provide valuable information on the energy release processes.…”

Section: Topics In This Issuementioning

confidence: 99%

New Eyes Looking at Solar Activity: Challenges for Theory and Simulations – Placing It into Context

et al. 2014

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Solar Cycle 24 has opened a new era in solar radio physics as we now have instruments that can probe solar processes from submillimeter to kilometer waves. New and upgraded instruments provide data that enable studies of both energetic particles and thermal plasma, enhancing our knowledge of solar eruptions and acceleration and propagation of particles, through the solar chromosphere and corona and into the interplanetary space. In this Topical Issue we highlight the new observational capabilities and discuss the theoretical issues connected to solar radio emission and interplanetary radio physics.

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Fine Structure of Metric Type IV Radio Bursts Observed with the ARTEMIS-IV Radio-Spectrograph: Association with Flares and Coronal Mass Ejections

Cited by 25 publications

References 46 publications

High resolution observations with Artemis-IV and the NRH

High resolution observations with Artemis-IV and the NRH

High-resolution observations with ARTEMIS-JLS and the NRH

New Eyes Looking at Solar Activity: Challenges for Theory and Simulations – Placing It into Context

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