Low Frequency Array (LOFAR)

Magnetic Field Geometry and Anisotropic Scattering Effects to Explain Puzzling LOFAR Solar Radio Burst Observations by D. L. Clarkson et al.

2025-02-04

Solar radio bursts are an indirect signature of accelerated electron beams from the solar atmosphere. These fast electrons generate Langmuir waves as they propagate through a decreasing plasma density and ultimately lead to the bright broadband radio emissions with a characteristic fast frequency drift in dynamic spectra. Density turbulence in the plasma can modulate this process, producing fine structures such as sub-second, narrowband striae and spikes. These fine structures may […]

Energetics of compressive waves in the solar corona by Francesco Azzollini et al

2024-07-02

Inelastic scattering off moving or oscillating density fluctuations leads to broadening of radio signals propagating in the solar corona and solar wind. Using an anisotropic density fluctuation model from the kinetic scattering theory for solar radio bursts, we deduce the plasma velocities (perpendicular to the line of sight) required to explain observations of spacecraft signal frequency broadening. The kinetic energy associated with these inferred bulk velocities cascades to smaller and […]

Anisotropic density turbulence variation from the low corona to 1 au as deduced from solar radio observations by E. Kontar et al.

2023-11-30

Density turbulence in the solar corona and solar wind is evident via the properties of solar radio bursts; angular scattering-broadening of extra-solar radio sources observed through the solar atmosphere, and can be measured in-situ in the solar wind. A viable density turbulence model should simultaneously explain all three types of density fluctuation observations. Solar radio bursts (e.g. Type I, II, III) observed below ~1 GHz are produced predominantly via plasma […]

Solar Radio Spikes and Type IIIb Striae Manifestations Triggered by a Coronal Mass Ejection by Clarkson et al

2023-04-11

Radio bursts are frequently emitted in the outer solar corona due to the acceleration of energetic electrons in solar flares and coronal mass ejections (CME). The shortest observed bursts are radio spikes, which have narrow spectral widths and are emitted over decades in frequency. Despite being studied for many years, imaging observations are sparse and restricted to localisation of the emission at decimetre frequencies (e.g. Benz, 2002). Recently, LOw Frequency […]

Temporal and Spatial Association Between Microwaves and Type III Bursts in the Upper Corona by Altyntsev et al.

2023-03-28

One important task connected with the corona heating problem is exploring the physical mechanisms that produce, accelerate, and transport energetic particles in the upper corona. The magnetic connectivity between the sources of meter emission in the upper corona and electron acceleration sites in low corona are studied using the temporal correlation between hard X-ray (HXR) bursts and type III emission (Kane 1972; Aschwanden et al. 1995; Reid & Vilmer 2017). […]

The frequency ratio and time delay of fundamental and harmonic components in solar radio bursts by X. Chen et al

2023-02-28

Solar radio bursts generated through the plasma emission mechanism produce radiation near the local plasma frequency (fundamental emission, hereafter, F) and double the plasma frequency (harmonic, hereafter, H). While the theoretical ratio of these two frequencies is close to 2, simultaneous observations give ratios ranging from 1.6 to 2, suggesting either a ratio different from 2, a delay of the F emission, or both. Observations suggest that a delayed F […]

LOFAR size and shape measurements of solar metric radio burst sources
by Gordovskyy et al

2022-04-19

The plasma density and magnetic field in the upper solar corona and inner heliosphere are not sufficient to produce detectable bremsstrahlung hard X-ray or gyrosynchrotron microwave emissions, making metric and decametric coherent radio emissions the only tool for probing energetic electrons in these layers of the solar atmosphere (e.g. McLean & Labrum 1985; Pick & Vilmer 2008 as reviews). This source of information is vital to understanding the underlying mechanisms […]

Langmuir wave motion observed in the most intense radio sources in the sky
by H. Reid and E. Kontar

2021-08-31

The Sun routinely produces energetic electrons in its outer atmosphere that subsequently travel through interplanetary space. These electron beams generate Langmuir waves in the background plasma, producing type III radio bursts that are the brightest radio sources in the sky (Suzuki & Dulk, 1985). These solar radio bursts also provide a unique opportunity to understand particle acceleration and transport which is important for our prediction of extreme space weather events […]

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