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Journal ArticleDOI

Major H alpha flares in centers of activity with very small or no spots

01 Aug 1970-Solar Physics (Kluwer Academic Publishers; D. Reidel Publishing Company ; Springer Science+Business Media)-Vol. 13, Iss: 2, pp 401-419
TL;DR: In the years 1956-1968 these flares represented ∼ 7% of all confirmed flares of importance ⪖ 2 as mentioned in this paper, in which the flares were of unusually long duration and rose to maximum intensity slowly.
Abstract: Major Hα flares (importance ⪖ 2) in plages with only small or no spots constitute a rare but well observed aspect of solar activity. Information relating to 83 such flares has been assembled and studied. In the years 1956–1968 these flares represented ∼ 7% of all confirmed flares of importance ⪖ 2. In general, the flares were of unusually long duration and rose to maximum intensity slowly. A flash phase was often absent or poorly defined. In a number of cases, the flare emission included two bright filaments more or less parallel. The flares usually occurred during the late, flare-poor phase of a center of activity, and their outbreak did not presage a resurgence of activity in subsequent rotations. The flares were frequently associated with the position of dark filaments.

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Citations
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Journal ArticleDOI
TL;DR: An overview of solar flares and associated phenomena, drawing upon a wide range of observational data primarily from the RHESSI era, is presented in this paper, where the focus is on different areas of flare phenomena (footpoints and ribbons, coronal sources, relationship to coronal mass ejections) and their interconnections.
Abstract: We present an overview of solar flares and associated phenomena, drawing upon a wide range of observational data primarily from the RHESSI era Following an introductory discussion and overview of the status of observational capabilities, the article is split into topical sections which deal with different areas of flare phenomena (footpoints and ribbons, coronal sources, relationship to coronal mass ejections) and their interconnections We also discuss flare soft X-ray spectroscopy and the energetics of the process The emphasis is to describe the observations from multiple points of view, while bearing in mind the models that link them to each other and to theory The present theoretical and observational understanding of solar flares is far from complete, so we conclude with a brief discussion of models, and a list of missing but important observations

774 citations


Cites background from "Major H alpha flares in centers of ..."

  • ...A small fraction of flares do occur in so-called “spotless” regions (Dodson & Hedeman 1970; Martin 1980), and largescale filament eruptions with flare-like properties can happen anywhere on the quiet Sun (e.g., Harvey et al. 1986)....

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Journal ArticleDOI
TL;DR: In this article, the authors put together what we have learned about coronal structures and phenomenology to synthesize a physical picture of the corona as a voluminous, thermally and electrically highlyconducting atmosphere responding dynamically to the injection of magnetic flux from below.
Abstract: This review puts together what we have learned about coronal structures and phenomenology to synthesize a physical picture of the corona as a voluminous, thermally and electrically highly-conducting atmosphere responding dynamically to the injection of magnetic flux from below. The synthesis describes complementary roles played by the magnetic heating of the corona, the different types of flares, and the coronal mass ejections as physical processes by which magnetic flux and helicity make their way from below the photosphere into the corona, and, ultimately, into interplanetary space. In these processes, a physically meaningful interplay among dissipative magnetohydrodynamic turbulence, ideal ordered flows, and magnetic helicity determines how and when the rich variety of relatively long-lived coronal structures, spawned by the emerged magnetic flux, will evolve quasi-steadily or erupt with the impressive energies characteristic of flares and coronal mass ejections. Central to this picture is the suggestion, based on recent theoretical and observational works, that the the emerged flux may take the form of a twisted flux rope residing principally in the corona. Such a flux rope is identified with the low-density cavity at the base of a coronal helmet, often but not always encasing a quiescent prominence. The flux rope may either be bodily transported into the corona from below the photosphere, or reform out of a state of flaring turbulence under some suitable constraint of magnetic-helicity conservation. The appeal of this synthesis is its physical simplicity and the manner it relates a large set of diverse phenomena into a self-consistent whole. The implications of this view point are discussed. The topics covered are: the large-scale corona; helmet streamers; quiescent prominences; coronal mass ejections; flares and heating; magnetic reconnection and magnetic helicity; and, the hydromagnetics of magnetic flux emergence.

497 citations

Journal ArticleDOI
TL;DR: In this article, the authors studied 8 yr of active region observations from the United States Air Force/Mount Wilson data set, supplied by the NOAA World Data Center, to confirm the relation between δ spots and large flares.
Abstract: We have studied 8 yr of active region observations from the United States Air Force/Mount Wilson data set, supplied by the NOAA World Data Center, to confirm the relation between δ spots and large flares We found that after correcting some errors we were able to describe relationships among active region size, peak flare soft X-ray (SXR) flux (measured by GOES 1-8 A flux), and magnetic classification We found the Solar Optical Observing Network magnetic classification to be reasonably accurate but its area measures to be inaccurate for many of the regions This is due partly to transcription errors and partly to wrong correction for limb foreshortening Errors could, however, be repaired by intercomparison of multiple observations We confirm Kunzel's original idea that regions classified βγδ produce many more large flares than other regions of comparable size Almost all substantial flares occurred in regions classified βγδ by the Air Force sites Each region larger than 1000 μh and classified βγδ had nearly 40% probability of producing flares classified X1 or greater Yet only a half-dozen of those, showing the "island delta" configuration, produced great activity There is a general trend for large regions to produce large flares, but it is less significant than the dependence on magnetic class

282 citations

Journal ArticleDOI
TL;DR: In this article, the authors focus on the processes that energize and trigger M-and X-class solar flares and associated flux-rope destabilizations and suggest a critical role for the emergence of twisted flux ropes into pre-existing strong field for many, if not all, of the active regions that produce M- or X class flares.

232 citations


Cites background from "Major H alpha flares in centers of ..."

  • ...The work of, e.g., Dodson and Hedeman (1970) and Ruzdjak et al. (1989) points out that whereas flares do occur in spotless regions, these account for only about 2% of all flares while the largest documented flare in soft X-rays of this type was classified as M1....

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Journal ArticleDOI
TL;DR: In this article, the impulsive phase of the flare dominates the energy and momentum in the electromagnetic field, not in the observable plasma, and also point out that energy and energy in this phase largely reside in the magnetic field.
Abstract: This article broadly reviews our knowledge of solar flares. There is a particular focus on their global properties, as opposed to the microphysics such as that needed for magnetic reconnection or particle acceleration as such. Indeed solar flares will always remain in the domain of remote sensing, so we cannot observe the microscales directly and must understand the basic physics entirely via the global properties plus theoretical inference. The global observables include the general energetics—radiation in flares and mass loss in coronal mass ejections (CMEs)—and the formation of different kinds of ejection and global wave disturbance: the type II radio-burst exciter, the Moreton wave, the EIT “wave”, and the “sunquake” acoustic waves in the solar interior. Flare radiation and CME kinetic energy can have comparable magnitudes, of order 1032 erg each for an X-class event, with the bulk of the radiant energy in the visible-UV continuum. We argue that the impulsive phase of the flare dominates the energetics of all of these manifestations, and also point out that energy and momentum in this phase largely reside in the electromagnetic field, not in the observable plasma.

179 citations

References
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Journal ArticleDOI
TL;DR: In this paper, a solar flare induced interplanetary shock and helium enriched driver gas observed on 13 February 1967, discussing wind velocity and plasma acceleration were discussed. But the authors did not consider the effects of solar flares.
Abstract: Solar flare induced interplanetary shock and helium enriched driver gas observed on 13 February 1967, discussing wind velocity and plasma acceleration

151 citations

Journal ArticleDOI
TL;DR: In this paper, four solar proton events observed by Explorers XII and XIV indicate that propagation of particles is a velocity dependent process, which is not the case for the current paper.
Abstract: Four solar proton events observed by Explorers XII and XIV indicate that propagation of particles is velocity dependent process

74 citations

Journal ArticleDOI
TL;DR: In this paper, a simple gravitational model for the flarelike brightenings of the chromosphere that follow most disparitions brusques (disappearing filaments) is presented, where the ascending prominence material is lifted out of the initially stable magnetic dips that characterize quiescent prominences and falls along the arched field lines into the bright areas.
Abstract: Here I present a simple gravitational model for the flarelike brightenings of the chromosphere that follow most disparitions brusques (disappearing filaments). I assume the ascending prominence material is lifted out of the initially stable magnetic dips that characterize quiescent prominences and falls along the arched field lines into the chromosphere where the kinetic energy of fall is dissipated in the bright areas. The examination of prominence and chromospheric characteristics leads naturally to many predictions and relations during and after prominence eruptions. In general the predictions are specific, but the observations of necessary detail and quality are nonexistent; however, the predictions appear to agree with the data that are available. The model appears to explain all non-active-region brightenings of the chromosphere that follow disparitions brusques and an unknown fraction of active-region flares. The conclusion is that two-ribbon flares are due to the disparitions brusques → chromospheric flarelike brightening mechanism. In this paper it will become clear that many specific observations in and out of active regions will be necessary to test the predictions of the model given here.

71 citations