Journal Article•
Evidence for MHD Pulsations in the Solar Corona
About: This article is published in Astronomy and Astrophysics.The article was published on 1970-11-01 and is currently open access. It has received 90 citations till now. The article focuses on the topics: Magnetohydrodynamics.
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TL;DR: In this paper, various versions of pulsation models are reviewed and classified in three groups according to their driver mechanisms: (1) Magnetic flux tube oscillations (the emissivity of trapped particles is modulated by a standing or propagating MHD wave), (2) cyclic self-organizing systems of plasma instabilities (wave-particle, wave-wave interactions), and (3) modulation of acceleration (acceleration/injection of particles into the source).
Abstract: ‘Pulsations’ include a wide range of phenomena from strictly sinusoidal oscillations up to quasiperiodic fine structures, observed in the radio, microwave and X-ray frequency range. The various versions of pulsation models are reviewed and classified in three groups according to their driver mechanisms: (1) Magnetic flux tube oscillations (the emissivity of trapped particles is modulated by a standing or propagating MHD wave), (2) cyclic self-organizing systems of plasma instabilities (wave-particle, wave-wave interactions), and (3) modulation of acceleration (acceleration/injection of particles into the source). Observational references illustrate the applicability of the models. In conclusion, discrimination criteria of models are discussed, in order to give a key for interpretation of observations.
180 citations
TL;DR: The discussion starts with a selection of observational discoveries that have brought magnetic waves to the forefront of the coronal heating discussion and a commentary on how the combination of theory and observations should help to understand and quantify magnetic wave heating of the solar atmosphere.
Abstract: Magnetic waves are a relevant component in the dynamics of the solar atmosphere. Their significance has increased because of their potential as a remote diagnostic tool and their presumed contribution to plasma heating processes. We discuss our current understanding of coronal heating by magnetic waves, based on recent observational evidence and theoretical advances. The discussion starts with a selection of observational discoveries that have brought magnetic waves to the forefront of the coronal heating discussion. Then, our theoretical understanding of the nature and properties of the observed waves and the physical processes that have been proposed to explain observations are described. Particular attention is given to the sequence of processes that link observed wave characteristics with concealed energy transport, dissipation and heat conversion. We conclude with a commentary on how the combination of theory and observations should help us to understand and quantify magnetic wave heating of the solar atmosphere.
137 citations
Cites background from "Evidence for MHD Pulsations in the ..."
...Early observations already pointed to the existence of quasi-periodic perturbations in solar coronal structures (see e.g., Billings, 1959; Rosenberg, 1970; Vernazza et al., 1975; Tsubaki, 1977; Trottet et al., 1979; Antonucci et al., 1984; Aschwanden, 1987; Deubner & Fleck, 1989)....
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TL;DR: The high resolution dynamic spectrogram between 320 and 160 MHz of the Type IV event which started at 13∶35 UT on the 2nd of March 1970 shows a remarkable richness of absorption-emission microstructures.
Abstract: The high resolution dynamic spectrogram between 320 and 160 MHz of the Type IV event which started at 13∶35 UT on the 2nd of March 1970 shows a remarkable richness of absorption-emission microstructures. These are morphologically analyzed into structure elements and patterns. The elements are normal and reversed intermediate drift bursts, which we call fiber bursts, medium band shortlived absorptions, broadband shortlived absorptions, broadband wedge shaped absorptions and a, sofar unknown, type which we call tadpole. The patterns are the pulsating structure, sequences of broadband shortlived absorptions, and patterns of almost parallel lines which we call zebra patterns. During the event a border frequency of about 230 MHz plays an important part, most clearly as a low frequency cut-off for the tadpole zebrapattern and as a zone of phase change in the pulsating structure. The macrostructure of this event, shown in a composite dynamic spectrogram, reveals features in the decimetric wavelength region that are related with the appearance of tadpole patterns in the region between 220 and 320 MHz.
105 citations
TL;DR: In this paper, a model for the acceleration of the emitting electrons and for the pulsations themselves is presented, which accounts both for the accelerating of the emitted electrons and the pulsation themselves.
Abstract: A CURIOUS but rare feature of the metre–wave continuum (type IV) radiation received from certain large solar flares is the pulsating structure which modulates the intensity in a periodic or quasi-periodic manner1,2. The modulation may persist for about l min or more and the period of the pulsation is typically of the order of 1 s. Of various explanations suggested, we consider the most satisfactory to be that of Rosenberg, in which the radiation is attributed to synchrotron radiation emitted by electrons in a magnetic flux tube embedded in the solar corona and the pulsations are attributed to modulation by standing magnetohydrodynamic (MHD) waves set up within the tube. We now present further evidence of this phenomenon and outline a model which accounts both for the acceleration of the emitting electrons and for the pulsations themselves. There is also evidence to suggest that energetic protons may be accelerated by the same process. We consider that the phenomenon affords a possible observational clue to a physical process by which solar cosmic rays can be generated high in the solar corona.
101 citations
TL;DR: In this paper, the fundamental structural elements of the coronal magnetic loops of the Sun and flaring stars are discussed, which are involved in phenomena such as stellar coronal heating, flare energy release, charged particle acceleration, and modulation of optical, radio, and X-ray emissions.
Abstract: The goal of this review is to outline some new ideas in the physics of coronal magnetic loops, the fundamental structural elements of the atmospheres of the Sun and flaring stars, which are involved in phenomena such as stellar coronal heating, flare energy release, charged particle acceleration, and the modulation of optical, radio, and X-ray emissions. The Alfven–Carlqvist view of a coronal loop as an equivalent electric circuit allows a good physical understanding of loop processes. Describing coronal loops as MHD-resonators explains various ways in which flaring emissions from the Sun and stars are modulated, whereas modeling them by magnetic mirror traps allows one to describe the dynamics and emission of high-energy particles. Based on these approaches, loop plasma and fast particle parameters are obtained and models for flare energy release and stellar corona heating are developed.
85 citations