solar radio bursts
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Solar Physics ◽  
2021 ◽  
Vol 296 (12) ◽  
Author(s):  
Larisa K. Kashapova ◽  
Dmitrii Y. Kolotkov ◽  
Elena G. Kupriyanova ◽  
Anastasiia V. Kudriavtseva ◽  
Chengming Tan ◽  
...  

2021 ◽  
Vol 923 (2) ◽  
pp. 268
Author(s):  
Guannan Gao ◽  
Qiangwei Cai ◽  
Shaojie Guo ◽  
Min Wang

Abstract A GOES M1.9 flare took place in active region AR 11153 on 2011 February 9. With a resolution of 200 kHz and a time cadence of 80 ms, the reverse-drifting (RS) type-III bursts, intermittent sequence of type-U bursts, drifting pulsation structure (DPS), and fine structures were observed by the Yunnan Observatories Solar Radio Spectrometer (YNSRS). Combined information revealed by the multiwavelength data indicated that after the DPS was observed by YNSRS, the generation rate of type-U bursts suddenly increased to 5 times what it had been. In this event, the generation rate of type-U bursts may depend on the magnetic-reconnection rate. Our observations are consistent with previous numerical simulation results. After the first plasmoid produced (plasma instability occurred), the magnetic-reconnection rate suddenly increased by 5 to 8 times. Furthermore, after the DPS, the frequency range of the turnover frequency of type-U bursts was obviously broadened to thrice what it was before, which indicates a fluctuation amplitude of the density in the loop top. Our observations also support numerical simulations during the flare-impulsive phase. Turbulence occurs at the top of the flare loop and the plasmoids can trap nonthermal particles, causing density fluctuation at the loop top. The observations are generally consistent with the results of numerical simulations, helping us to better understand the characteristics of the whole physical process of eruption.


2021 ◽  
Vol 922 (2) ◽  
pp. 128
Author(s):  
Sherry Chhabra ◽  
James A. Klimchuk ◽  
Dale E. Gary

Abstract There is a wide consensus that the ubiquitous presence of magnetic reconnection events and the associated impulsive heating (nanoflares) are strong candidates for solving the solar coronal heating problem. Whether nanoflares accelerate particles to high energies like full-sized flares is unknown. We investigate this question by studying the type III radio bursts that the nanoflares may produce on closed loops. The characteristic frequency drifts that type III bursts exhibit can be detected using a novel application of the time-lag technique developed by Viall & Klimchuk (2012) even when there are multiple overlapping events. We present a simple numerical model that simulates the expected radio emission from nanoflares in an active region, which we use to test and calibrate the technique. We find that in the case of closed loops the frequency spectrum of type III bursts is expected to be extremely steep such that significant emission is produced at a given frequency only for a rather narrow range of loop lengths. We also find that the signature of bursts in the time-lag signal diminishes as: (1) the variety of participating loops within that range increases; (2) the occurrence rate of bursts increases; (3) the duration of bursts increases; and (4) the brightness of bursts decreases relative to noise. In addition, our model suggests a possible origin of type I bursts as a natural consequence of type III emission in a closed-loop geometry.


2021 ◽  
Vol 922 (1) ◽  
pp. 82
Author(s):  
Gennady Chernov ◽  
Valery Fomichev

Abstract Type II solar radio bursts are among the most powerful events in the solar radio emission in the meter wavelength range. It is generally accepted that the agents generating type II radio bursts are magnetohydrodynamic shock waves. But the relationship between the shock waves and the other manifestations of the large-scale disturbances in the solar atmosphere (coronal mass ejections, Morton waves, EUW waves) remains unclear. To clarify a problem, it is important to determine the conditions of generation of type II radio bursts. Here, the model of the radio source is based on the generation of radio emission within the front of the collisionless shock wave where the Buneman instability of plasma waves is developed. In the frame of this model, the Alfvén magnetic Mach number must exceed the critical value, and there is a strict restriction on the perpendicularity of the front. The model allows us to obtain the information about the parameters of the shock waves and the parameters of the medium by the parameters of type II bursts. The estimates, obtained in this paper for several events with the band splitting of the fundamental and harmonic emission bands of the type II bursts, confirm the necessary conditions of the model. In this case the registration of type II radio bursts is an indication of the propagation of shock waves in the solar atmosphere, and the absence of type II radio bursts is not an indication of the absence of shock waves. Such a situation should be taken into account when investigating the relationship between type II radio bursts and other manifestations of solar activity.


Author(s):  
Abdallah Hamini ◽  
Gabriel Auxepaules ◽  
Lionel Birée ◽  
Guy Kenfack ◽  
Alain Kerdraon ◽  
...  

Radio bursts are sensitive tracers of non-thermal electron populations in the solar corona. They are produced by electron beams and shock waves propagating through the corona and the Heliosphere, and by trapped electron populations in coronal mass ejections (CMEs) and in quiescent active regions. Combining space borne and ground-based radio spectrographs allows one to track disturbances all the way between the low corona, near or at the sites of particle acceleration, and the spacecraft. Radio observations are therefore a significant tool in probing the solar origin of heliospheric disturbances, which is a central research topic as   witnessed by the Parker Solar Probe and Solar Orbiter missions. The full scientific return of these projects needs vigorous ground-based support, which at radio wavelengths covers altitudes up to about a solar radius above the photosphere. Besides research in solar and heliospheric physics, monitoring solar radio bursts also supports space weather services. On occasion radio bursts can themselves be a space weather hazard. The Nan\c{c}ay radio astronomy station in central France has a long tradition of monitoring radio emission at decimetre-to-metre wavelengths. This article describes the radio spectrograph ORFEES ({\it Observations Radiospectrographiques pour FEDOME et l'Etude des Eruptions Solaires}). It observes the whole-Sun flux density between 144 and 1004 MHz, which pertains to regions between the low corona and about half a solar radius above the photosphere. ORFEES is the result of a partnership between Observatoire de Paris and the French Air Force, which operates the experimental space weather service FEDOME. The primary use of the instrument at Paris Observatory is the astrophysical observation. Low-resolution data with rapid availability are presently produced for the French Air Force. Similar information can be made available to a broader range of space-weather service providers. This article gives an overview of the instrument design and the access to the data, and shows a few illustrative observations.


2021 ◽  
Vol 9 ◽  
Author(s):  
Weidan Zhang ◽  
Fabao Yan ◽  
Fuyun Han ◽  
Ruopu He ◽  
Enze Li ◽  
...  

Solar radio bursts can be used to study the properties of solar activities and the underlying coronal conditions on the basis of the present understanding of their emission mechanisms. With the construction of observational instruments, around the world, a vast volume of solar radio observational data has been obtained. Manual classifications of these data require significant efforts and human labor in addition to necessary expertise in the field. Misclassifications are unavoidable due to subjective judgments of various types of radio bursts and strong radio interference in some events. It is therefore timely and demanding to develop techniques of auto-classification or recognition of solar radio bursts. The latest advances in deep learning technology provide an opportunity along this line of research. In this study, we develop a deep convolutional generative adversarial network model with conditional information (C-DCGAN) to auto-classify various types of solar radio bursts, using the solar radio spectral data from the Culgoora Observatory (1995, 2015) and the Learmonth Observatory (2001, 2019), in the metric decametric wavelengths. The technique generates pseudo images based on available data inputs, by modifying the layers of the generator and discriminator of the deep convolutional generative adversarial network. It is demonstrated that the C-DCGAN method can reach a high-level accuracy of auto-recognition of various types of solar radio bursts. And the issue caused by inadequate numbers of data samples and the consequent over-fitting issue has been partly resolved.


2021 ◽  
Vol 21 (6) ◽  
pp. 145
Author(s):  
Javier Alonso Rengifo ◽  
Verónica Loaiza-Tacuri ◽  
José Bazo ◽  
Walter Robert Guevara Day

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