Solar Radio Emissions

A special issue of Universe (ISSN 2218-1997). This special issue belongs to the section "Solar System".

Deadline for manuscript submissions: closed (30 April 2023) | Viewed by 8250

Special Issue Editors


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Guest Editor
Division of Solar Physics, National Astronomical Observatories of Chinese Academy of Sciences, Beijing 100192, China
Interests: solar radio astronomy; solar physics; plasma astrophysics
Special Issues, Collections and Topics in MDPI journals

E-Mail Website
Guest Editor
Division of Solar Physics, National Astronomical Observatories of Chinese Academy of Sciences, Beijing 100192, China
Interests: solar radio astronomy; solar physics

Special Issue Information

Dear Colleagues,

Solar radio astronomy is a burgeoning field affecting almost all branches of solar physics, space weather, and even other branches of astrophysics. Solar radio emissions come not only from various kinds of solar activities, but also from the Sun, from the photosphere, through the chromosphere to the corona, and far into interplanetary space; the related frequency spans more than 5 orders of magnitude from several hundreds of GHz (sub-mm wavelength) down to sub-MHz (km wavelength). Radio emissions are very sensitive to the acceleration and propagation of nonthermal electrons, plasma instabilities, magnetic fields and their variations, magnetic reconnections and violent energy releases, various scales of shock waves, etc. Solar radio observations can possibly be applied to measure the magnetic fields in the very hot and diluted coronal atmosphere, to reveal the mystery of coronal heating, to detect energetic particle acceleration and propagation, to explore the origin of solar violent eruptions (including solar flares, CMEs, various scales of jets, etc.) and track their temporal and spatial evolutions, and to provide crucial information for predicting space weather.

Recently, a series of advanced solar radio telescopes were put into operation and obtained a large amount of observation data. These new instruments include MUSER, EVOSA, SRH, LOFAR, MWA, ALMA and PSP. Through their high-sensitivity and high-resolution solar radio observations, we have the opportunity to give new explanations to the above important problems, discover new physics knowledge and make new scientific breakthroughs. In order to exhibit the new, up-to-date progress obtained in this domain, we are organizing the Special Issue, “Solar Radio Emissions”, and invite colleagues to submit their new manuscripts on one or more of the following topics for this Special Issue:

  • New observational phenomena of solar radio emissions;
  • New discoveries of spectral fine structures of solar radio bursts;
  • New theoretical explanations of solar radio bursts, including an explanation of the origin and formation mechanism of the solar radio Zebra pattern, fiber bursts, spike groups, the fine structures of type II, III, and IV bursts, and multi-timescale QPP;
  • Radio signals of magnetic reconnections and shock waves;
  • Radio precursors of solar flares and CMEs;
  • Diagnostics of coronal magnetic fields from radio emissions;
  • Radio emissions related to particle acceleration and propagations;
  • Advanced methods to predict solar activities and space weather by using solar radio observations;
  • Possible clues for new physics knowledge hidden by solar radio emissions, such as signals for dark matter, solar interior structures and dynamics, etc.

Prof. Dr. Baolin Tan
Dr. Jing Huang
Guest Editors

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Keywords

  • solar radio emissions
  • magnetic reconnection
  • particle acceleration
  • propagation
  • shock wave

Published Papers (7 papers)

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Research

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14 pages, 1385 KiB  
Article
The Non-Thermal Radio Emissions of the Solar Transition Region and the Proposal of an Observational Regime
by Baolin Tan, Jing Huang, Yin Zhang, Yuanyong Deng, Linjie Chen, Fei Liu, Jin Fan and Jun Shi
Universe 2024, 10(2), 82; https://doi.org/10.3390/universe10020082 - 08 Feb 2024
Viewed by 1004
Abstract
The transition region is a very thin but most peculiar layer in the solar atmosphere located between the solar chromosphere and the corona. It is a key region for understanding coronal heating, solar eruption triggers, and the origin of solar winds. Here, almost [...] Read more.
The transition region is a very thin but most peculiar layer in the solar atmosphere located between the solar chromosphere and the corona. It is a key region for understanding coronal heating, solar eruption triggers, and the origin of solar winds. Here, almost all physical parameters (density, temperature, and magnetic fields) have the maximum gradient. Therefore, this region should be highly dynamic, including fast energy releasing and transporting, plasma heating, and particle accelerating. The physical processes can be categorized into two classes: thermal and non-thermal processes. Thermal processes can be observed at ultraviolet (UV) and extreme ultraviolet (EUV) wavelengths via multi-wavelength images. Non-thermal processes accelerate non-thermal electrons and produce radio emissions via the gyrosynchrotron mechanism resulting from the interaction between the non-thermal electrons and magnetic fields. The frequency range spans from several GHz to beyond 100 GHz, in great number of bursts with narrowband, millisecond lifetime, rapid frequency drifting rates, and being referred to as transition region small-scale microwave bursts (TR-SMBs). This work proposes a new type of Solar Ultra-wide Broadband Millimeter-wave Spectrometer (SUBMS) that can be used to observe TR-SMBs. From SUBMS observations, we can derive rich dynamic information about the transition region, such as information about non-thermal energy release and propagation, the flows of plasma and energetic particles, the magnetic fields and their variations, the generation and transportation of various waves, and the formation and evolution of the source regions of solar eruptions. Such an instrument can actually detect the non-thermal signals in the transition region during no flare as well as the eruptive high-energy processes during solar flares. Full article
(This article belongs to the Special Issue Solar Radio Emissions)
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8 pages, 660 KiB  
Communication
Diagnostics of Flare Loop Parameters in Shrinkage and Ascent Stages Using Radio, X-ray, and UV Emission
by Valery Zaitsev and Alexander Stepanov
Universe 2023, 9(6), 261; https://doi.org/10.3390/universe9060261 - 30 May 2023
Viewed by 706
Abstract
We propose the diagnostics of plasma parameters in flare loops using the data of multi-wavelength observations in both shrinkage and expansion phases of the loops. The approach of a flare loop as an equivalent electric circuit is applied. We show that depending on [...] Read more.
We propose the diagnostics of plasma parameters in flare loops using the data of multi-wavelength observations in both shrinkage and expansion phases of the loops. The approach of a flare loop as an equivalent electric circuit is applied. We show that depending on plasma loop parameters, the shrinkage may be accompanied by an increase in the electric current in the loop rather than a decrease. The number density, temperature, electric current, radius, loop-top altitude, and loop volume are determined for the flare events on 16 April 2002 and 24 August 2002. Full article
(This article belongs to the Special Issue Solar Radio Emissions)
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13 pages, 1969 KiB  
Article
Quasi-Periodic Pulsations in an M-Class Solar Flare
by Jun Xu, Zongjun Ning, Dong Li and Fanpeng Shi
Universe 2023, 9(5), 215; https://doi.org/10.3390/universe9050215 - 30 Apr 2023
Cited by 1 | Viewed by 836
Abstract
We have studied the quasi-periodic pulsations (QPPs) of the M2.3 flare that occurred in the active region NOAA 12172 on 23 September 2014. Through the fast Fourier transform (FFT) method, we decompose the flare light curves into fast- and slowly-varying components, and the [...] Read more.
We have studied the quasi-periodic pulsations (QPPs) of the M2.3 flare that occurred in the active region NOAA 12172 on 23 September 2014. Through the fast Fourier transform (FFT) method, we decompose the flare light curves into fast- and slowly-varying components, and the cut-off threshold is 100 s. We find that the QPPs have a period of 40 s at soft X-ray (SXR), hard X-ray (HXR), radio and ultraviolet (UV). Based on the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO), we find that the QPPs take place at the same time interval as the flare ribbon separation, and that the QPPs seem to originate from the flare ribbons. Our observations tend to support the mechanism of the periodic nonthermal electron injection during the flare eruption. Full article
(This article belongs to the Special Issue Solar Radio Emissions)
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12 pages, 6808 KiB  
Communication
Multi-Periodicity of High-Frequency Type III Bursts as a Signature of the Fragmented Magnetic Reconnection
by Marian Karlický and Ján Rybák
Universe 2023, 9(2), 92; https://doi.org/10.3390/universe9020092 - 09 Feb 2023
Viewed by 883
Abstract
Using the radio spectra of the 2 April 2022 eruptive flare, we analyze a group of highfrequency type III bursts by our new wavelet method. In this analysis, we found a multi-periodicity of these bursts that is interpreted by the electron beams accelerated [...] Read more.
Using the radio spectra of the 2 April 2022 eruptive flare, we analyze a group of highfrequency type III bursts by our new wavelet method. In this analysis, we found a multi-periodicity of these bursts that is interpreted by the electron beams accelerated in the fragmented magnetic reconnection in the rising magnetic rope. We propose that each period in these type III bursts is a result of the periodic interaction of sub-ropes formed in the rising magnetic rope. In each interaction, the period depends on the diameter of interacting sub-ropes and local Alfvén velocity. This interpretation is supported by detection of the specific EUV structure which was, according to our knowledge, observed for the first time. All proposed processes occur in the rising magnetic rope. Thus, this flare deviates from the standard flare model, where the main magnetic reconnection is located below the rising magnetic rope. Full article
(This article belongs to the Special Issue Solar Radio Emissions)
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10 pages, 2910 KiB  
Article
Classification of Solar Radio Spectrum Based on Swin Transformer
by Jian Chen, Guowu Yuan, Hao Zhou, Chengming Tan, Lei Yang and Siqi Li
Universe 2023, 9(1), 9; https://doi.org/10.3390/universe9010009 - 23 Dec 2022
Cited by 2 | Viewed by 1339
Abstract
Solar radio observation is a method used to study the Sun. It is very important for space weather early warning and solar physics research to automatically classify solar radio spectrums in real time and judge whether there is a solar radio burst. As [...] Read more.
Solar radio observation is a method used to study the Sun. It is very important for space weather early warning and solar physics research to automatically classify solar radio spectrums in real time and judge whether there is a solar radio burst. As the number of solar radio burst spectrums is small and uneven, this paper proposes a classification method for solar radio spectrums based on the Swin transformer. First, the method transfers the parameters of the pretrained model to the Swin transformer model. Then, the hidden layer weights of the Swin transformer are frozen, and the fully connected layer of the Swin transformer is trained on the target dataset. Finally, parameter tuning is performed. The experimental results show that the method can achieve a true positive rate of 100%, which is more accurate than previous methods. Moreover, the number of our model parameters is only 20 million, which is 80% lower than that of the traditional VGG16 convolutional neural network with more than 130 million parameters. Full article
(This article belongs to the Special Issue Solar Radio Emissions)
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Review

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46 pages, 25189 KiB  
Review
Fine Structure of Solar Metric Radio Bursts: ARTEMIS-IV/JLS and NRH Observations
by Costas Alissandrakis, Alexander Hillaris, Costas Bouratzis and Spyros Armatas
Universe 2023, 9(10), 442; https://doi.org/10.3390/universe9100442 - 30 Sep 2023
Cited by 1 | Viewed by 1351
Abstract
Radio bursts provide important diagnostics of energetic phenomena of the Sun. In particular, bursts in decimetric and metric wavelengths probe the physical conditions and the energy release processes in the low corona as well as their association with heliospheric phenomena. The advent of [...] Read more.
Radio bursts provide important diagnostics of energetic phenomena of the Sun. In particular, bursts in decimetric and metric wavelengths probe the physical conditions and the energy release processes in the low corona as well as their association with heliospheric phenomena. The advent of spectral radio data with high time and high frequency resolution has provided a wealth of information on phenomena of short duration and narrow bandwidth. Of particular value are spectral data combined with imaging observations at specific frequencies. In this work we briefly review the results of a series of observations comprised from high-sensitivity, low-noise dynamic spectra obtained with the acousto-optic analyzer (SAO) of the ARTEMIS-IV/JLS solar radiospectrograph, in conjunction with high time-resolution images from the Nançay Radioheliograph (NRH). Our studies include fine structures embedded in type-IV burst continua (mostly narrow-band “spikes” and intermediate drift “fiber” bursts) and spike-like structures detected near the front of type-II bursts. The implications of the observational results to theoretical models are discussed. Full article
(This article belongs to the Special Issue Solar Radio Emissions)
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16 pages, 739 KiB  
Review
Solar Radio Emissions and Ultralight Dark Matter
by Haipeng An, Shuailiang Ge and Jia Liu
Universe 2023, 9(3), 142; https://doi.org/10.3390/universe9030142 - 07 Mar 2023
Cited by 6 | Viewed by 1212
Abstract
Ultralight axions and dark photons are well-motivated dark matter candidates. Inside the plasma, once the mass of ultralight dark matter candidates equals the plasma frequency, they can resonantly convert into electromagnetic waves, due to the coupling between the ultralight dark matter particles and [...] Read more.
Ultralight axions and dark photons are well-motivated dark matter candidates. Inside the plasma, once the mass of ultralight dark matter candidates equals the plasma frequency, they can resonantly convert into electromagnetic waves, due to the coupling between the ultralight dark matter particles and the standard model photons. The converted electromagnetic waves are monochromatic. In this article, we review the development of using radio detectors to search for ultralight dark matter conversions in the solar corona and solar wind plasma. Full article
(This article belongs to the Special Issue Solar Radio Emissions)
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