scholarly journals Fibre structure of decametric type II radio bursts as a manifestation of emission propagation effects in a disturbed near-solar plasma

2009 ◽  
Vol 27 (10) ◽  
pp. 3933-3940 ◽  
Author(s):  
A. N. Afanasiev
Keyword(s):  
Large Scale ◽  
Inhomogeneous Plasma ◽  
Density Fluctuations ◽  
Formation Mechanisms ◽  
Radio Bursts ◽  
Type Ii ◽  
Radio Waves ◽  
Propagation Effects ◽  
Type Ii Radio Bursts ◽  
Electron Density Fluctuations

Abstract. This paper addresses the fine structure of solar decametric type II radio bursts in the form of drifting narrowband fibres on the dynamic spectrum. Observations show that this structure appears in those events where there is a coronal mass ejection (CME) traveling in the near-solar space ahead of the shock wave responsible for the radio burst. The diversity in observed morphology of fibres and values of their parameters implies that the fibres may be caused by different formation mechanisms. The burst emission propagates through extremely inhomogeneous plasma of the CME, so one possible mechanism can be related to radio propagation effects. I suggest that the fibres in some events represent traces of radio emission caustics, which are formed due to regular refraction of radio waves on the large-scale inhomogeneous structure of the CME front. To support this hypothesis, I have modeled the propagation of radio waves through inhomogeneous plasma of the CME, taking into consideration the presence of electron density fluctuations in it. The calculations, which are based on the Monte Carlo technique, indicate that, in particular, the emission of the fibres should be harmonic. Moreover, the mechanism under consideration suggests that in solar observations from two different points in space, the observed sets of fibres can be shifted in frequency with respect to one another or can have a different structure. This potentially can be used for identifying fibres caused by the propagation effects.

scholarly journals LOFAR observations of a jet-driven piston shock in the low solar corona

2021 ◽  
Author(s):  
Ciara Maguire ◽  
Eoin Carley ◽  
Pietro Zucca ◽  
Nicole Vilmer ◽  
Peter Gallagher
Keyword(s):  
Radio Burst ◽  
Extreme Ultraviolet ◽  
Large Angle ◽  
Low Frequency ◽  
Density Fluctuations ◽  
Plasma Emission ◽  
Type Ii ◽  
Radio Waves ◽  
Type Ii Radio Bursts ◽  
Electron Density Fluctuations

<p>The Sun produces highly dynamic and eruptive events that can drive shocks through the corona. These shocks can accelerate electrons, which result in plasma emission in the form of a type II radio burst. Despite a large number of type II radio bursts observations, the precise origin of coronal shocks is still subject to investigation. Here we present a well-observed solar eruptive event that occurred on 16 October 2015, focusing on a jet observed in the extreme ultraviolet by the SDO Atmospheric Imaging Assembly, a streamer observed in white-light by the Large Angle and  Spectrometric Coronagraph, and a metric type II radio burst observed by the LOw-Frequency Array (LOFAR) radio telescope. For the first time, LOFAR has interferometrically imaged the fundamental and harmonic sources of a type II radio burst and revealed that the sources did not appear to be co-spatial, as would be expected from the plasma emission mechanism. We correct for the separation between the fundamental and harmonic using a model which accounts for the scattering of radio waves by electron density fluctuations in a turbulent plasma. This allows us to show the type II radio sources were located ∼0.5 R<sub>sun</sub> above the jet and propagated at a speed of ∼1000 km s<sup>−1</sup>, which was significantly faster than the jet speed of ∼200 km s<sup>−1</sup>. This suggests that the type II burst was generated by a piston shock driven by the jet in the low corona.</p>

scholarly journals The Relation Between Large-Scale Coronal Propagating Fronts and Type II Radio Bursts

Solar Physics ◽  
2014 ◽  
Vol 289 (12) ◽  
pp. 4589-4606 ◽  
Author(s):  
Nariaki V. Nitta ◽  
Wei Liu ◽  
Nat Gopalswamy ◽  
Seiji Yashiro
Keyword(s):  
Large Scale ◽  
Radio Bursts ◽  
Type Ii ◽  
Type Ii Radio Bursts

Solar and interplanetary parameters of CMEs with and without type II radio bursts

2012 ◽  
Vol 50 (4) ◽  
pp. 516-525 ◽  
Author(s):  
A. Mujiber Rahman ◽  
S. Umapathy ◽  
A. Shanmugaraju ◽  
Y.-J. Moon
Keyword(s):  
Radio Bursts ◽  
Type Ii ◽  
Type Ii Radio Bursts

scholarly journals Coronal electron density distributions estimated from CMEs, DH type II radio bursts, and polarized brightness measurements

2016 ◽  
Vol 121 (4) ◽  
pp. 2853-2865 ◽  
Author(s):  
Jae‐Ok Lee ◽  
Y.‐J. Moon ◽  
Jin‐Yi Lee ◽  
Kyoung‐Sun Lee ◽  
R.‐S. Kim
Keyword(s):  
Electron Density ◽  
Radio Bursts ◽  
Type Ii ◽  
Density Distributions ◽  
Type Ii Radio Bursts ◽  
Coronal Electron

Investigation of X-class Flare-Associated Coronal Mass Ejections with and without DH Type II Radio Bursts

Solar Physics ◽  
2015 ◽  
Vol 290 (11) ◽  
pp. 3365-3377 ◽  
Author(s):  
M. Bendict Lawrance ◽  
A. Shanmugaraju ◽  
Bojan Vršnak
Keyword(s):  
Coronal Mass Ejections ◽  
Radio Bursts ◽  
Type Ii ◽  
Type Ii Radio Bursts ◽  
Class Flare

Fine structure of decametric type II radio bursts

2007 ◽  
Vol 33 (3) ◽  
pp. 192-202 ◽  
Author(s):  
G. P. Chernov ◽  
A. A. Stanislavsky ◽  
A. A. Konovalenko ◽  
E. P. Abranin ◽  
V. V. Dorovsky ◽  
...  
Keyword(s):  
Fine Structure ◽  
Radio Bursts ◽  
Type Ii ◽  
Type Ii Radio Bursts

scholarly journals Optical Observations of the Solar Disturbances Causing Type II Radio Bursts

1958 ◽  
Vol 11 (3) ◽  
pp. 353 ◽  
Author(s):  
RG Giovanelli ◽  
JA Roberts
Keyword(s):  
Subsequent Development ◽  
Optical Observations ◽  
Radio Bursts ◽  
Type Ii ◽  
Type Ii Radio Bursts ◽  
Solar Disturbances ◽  
Dark Filament

Identifications have been established for the solar optical events associated with a number of type II radio bursts. Near or at the limb these have been ejections with velocities exceeding that of sound in the corona. Where the event has been on the disk there has usually been a very bright flare, with some evidence of dark filament activity. In two cases the event was the disappearance (i.e. ejection) of a filament with the subsequent development of flares on either side.

scholarly journals Statistical Measurements of Dispersion Measure Fluctuations of FRBs

2021 ◽  
Vol 922 (2) ◽  
pp. L31
Author(s):  
Siyao Xu ◽  
David H. Weinberg ◽  
Bing Zhang
Keyword(s):  
Electron Density ◽  
Large Scale ◽  
Density Fluctuations ◽  
Clear Correlation ◽  
Dispersion Measure ◽  
Large Dispersion ◽  
Dispersion Measures ◽  
The Difference ◽  
Electron Density Fluctuations ◽  
Scale Turbulence

Abstract Extragalactic fast radio bursts (FRBs) have large dispersion measures (DMs) and are unique probes of intergalactic electron density fluctuations. By using the recently released First CHIME/FRB Catalog, we reexamined the structure function (SF) of DM fluctuations. It shows a large DM fluctuation similar to that previously reported in Xu & Zhang, but no clear correlation hinting toward large-scale turbulence is reproduced with this larger sample. To suppress the distortion effect from FRB distances and their host DMs, we focus on a subset of CHIME catalog with DM < 500 pc cm−3. A trend of nonconstant SF and nonzero correlation function (CF) at angular separations θ less than 10° is seen, but with large statistical uncertainties. The difference found between SF and that derived from CF at θ ≲ 10° can be ascribed to the large statistical uncertainties or the density inhomogeneities on scales on the order of 100 Mpc. The possible correlation of electron density fluctuations and inhomogeneities of density distribution should be tested when several thousands of FRBs are available.

scholarly journals Analyzing the propagation of EUV waves and their connection with type II radio bursts by combining numerical simulations and multi-instrument observations

2020 ◽  
Vol 644 ◽  
pp. A90
Author(s):  
A. Koukras ◽  
C. Marqué ◽  
C. Downs ◽  
L. Dolla
Keyword(s):  
Magnetic Field ◽  
Wave Front ◽  
Ray Tracing ◽  
Radio Burst ◽  
Radio Bursts ◽  
Type Ii ◽  
Fast Mode ◽  
Type Ii Radio Bursts ◽  
The Magnetic Field ◽  
Burst Emission

Context. EUV (EIT) waves are wavelike disturbances of enhanced extreme ultraviolet (EUV) emission that propagate away from an eruptive active region across the solar disk. Recent years have seen much debate over their nature, with three main interpretations: the fast-mode magneto-hydrodynamic (MHD) wave, the apparent wave (reconfiguration of the magnetic field), and the hybrid wave (combination of the previous two). Aims. By studying the kinematics of EUV waves and their connection with type II radio bursts, we aim to examine the capability of the fast-mode interpretation to explain the observations, and to constrain the source locations of the type II radio burst emission. Methods. We propagate a fast-mode MHD wave numerically using a ray-tracing method and the WKB (Wentzel-Kramers-Brillouin) approximation. The wave is propagated in a static corona output by a global 3D MHD Coronal Model, which provides density, temperature, and Alfvén speed in the undisturbed coronal medium (before the eruption). We then compare the propagation of the computed wave front with the observed wave in EUV images (PROBA2/SWAP, SDO/AIA). Lastly, we use the frequency drift of the type II radio bursts to track the propagating shock wave, compare it with the simulated wave front at the same instant, and identify the wave vectors that best match the plasma density deduced from the radio emission. We apply this methodology for two EUV waves observed during SOL2017-04-03T14:20:00 and SOL2017-09-12T07:25:00. Results. The simulated wave front displays a good qualitative match with the observations for both events. Type II radio burst emission sources are tracked on the wave front all along its propagation. The wave vectors at the ray-path points that are characterized as sources of the type II radio burst emission are quasi-perpendicular to the magnetic field. Conclusions. We show that a simple ray-tracing model of the EUV wave is able to reproduce the observations and to provide insight into the physics of such waves. We provide supporting evidence that they are likely fast-mode MHD waves. We also narrow down the source region of the radio burst emission and show that different parts of the wave front are responsible for the type II radio burst emission at different times of the eruptive event.

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