Propagation Effects in Quiet Sun Observations at Meter Wavelengths
by R. Sharma and D. Oberoi

2021-02-02 187 views

The quiet Sun coronal emission dominantly comes from thermal bremsstrahlung. As this radiation traverses the coronal medium on its way to the Earthbound observer, the coronal optical depth, τ, along typical ray paths is neither low enough to be approximated as optically thin, nor high enough to be treated as optically thick. On its way to the observer, it gets modified substantially due to propagation effects —primarily refraction and scattering—through the […]

Electromagnetic Emission Produced by Three-wave Interactions in a Plasma with Continuously Injected Counterstreaming Electron Beams
by Vladimir Annenkov and Igor Timofeev

2021-01-19 205 views

Weakly turbulent processes of three-wave interactions between Langmuir and electromagnetic waves in plasma with unstable electron flows are believed to be the main cause of type II and III solar radio emissions. The narrow band of type II bursts requires assuming that this radiation is generated in some local regions of shock fronts traveling in the solar corona, where the specific conditions for the enhancement of electromagnetic emissions near the […]

An Explanation of Subsecond Time Evolution of Type III Solar Radio Burst Sources at Fundamental and Harmonic Frequencies
by X. Chen et al

2020-12-14 232 views

Recent studies (Kontar et al. 2017) of a Type III–IIIb burst observed by LOFAR (van Haarlem et al. 2013) indicated that the temporal variations in the positions and source sizes do not fit into the standard picture of type III solar radio bursts and require a better understanding of radio-wave transport. With the aim of explaining the observed properties of type III–IIIb solar radio bursts, we use radio-wave simulations of radio-wave […]

Estimate of Plasma Temperatures across a CME-driven Shock from a Comparison between EUV and Radio Data
by F. Frassati et al.*

2020-12-01 165 views

Type II radio bursts, produced near the local plasma frequency and/or its harmonic by energetic electrons accelerated by shock waves moving outward through the inner heliosphere, have long been recognized as evidence of shock waves origin and propagation in the solar corona. In this work, we analyze the early evolution of a coronal shock wave, associated with a prominence eruption, with the aim of investigating the properties of the compressed […]

Radio bursts in the 2017 September 6, X9.3 flare
by M. Karlicky and J. Rybak

2020-11-17 256 views

Radio bursts and their fine structures are an integral part of solar flares. Although many of them are known as e.g. type II, III, V, J, U, and IV, still some unique bursts and fine structures, not observed so far, can be detected. This is the case of the X9.3 flare observed on September 6, 2017, where we found not only several unique bursts and fine structures, but also their […]

Magnetic Reconnection during the Post-impulsive Phase of a Long-duration Solar Flare
by S. Yu et al.

2020-10-27 222 views

Magnetic reconnection, a fundamental process in astrophysical environment plasma is believed to facilitate the release of energy stored in the magnetic field. However, where the magnetic reconnections occur, how and where the released magnetic energy is transported, and how it is converted to other forms remain unclear. Here, we report well-connected observational signatures of magnetic reconnection, plasma heating, and electron acceleration observed during the post-impulsive gradual phase of the X8.2-class […]

Low frequency radio observations of the ‘quiet’ corona during the descending phase of sunspot cycle 24
by R. Ramesh et al.*

2020-10-13 303 views

The shape, size and electron density (Ne) of the corona varies with the sunspot cycle, which is now very well established by white-light observations. In our study, we investigated the ‘quiet’ solar corona (i.e., the corona distinct from emission due to transient and long-lasting discrete sources) at radio frequencies during the descending phase of sunspot cycle 24. We used the radio images obtained with the Gauribidanur RAdioheliograPH (GRAPH; Ramesh1998) at […]

Microwave Spectral Imaging of an Erupting Magnetic Flux Rope During a Large Solar Flare
by B. Chen et al.*

2020-09-22 343 views

Magnetic flux ropes are believed to be the centerpiece of the three-part structure of coronal mass ejections. In the standard model of eruptive solar flares, flux rope eruption also induces the impulsive flare energy release through magnetic reconnection. Signatures of flare-associated flux ropes in the low solar corona have been frequently reported in extreme ultraviolet (EUV) wavelengths, particularly the so-called EUV “hot channel” structures (see, e.g., Cheng et al. 2017 […]

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