Characteristics of Solar Flares.
1951; IOP Publishing; Volume: 114; Linguagem: Inglês
10.1086/145473
ISSN1538-4357
Autores Tópico(s)Astronomical Observations and Instrumentation
Resumoview Abstract Citations (29) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Characteristics of Solar Flares. Richardson, Robert S. Abstract Attention is called to certain characteristics of the changes in area of solar flares which, on a much reduced time scale, are suggestive of the light-curves of novae. Different types of flares are discussed on the basis of these characteristics. A flare has been called "fast" if it attains maximum area within less than 0.4 of its lifetime. A flare is `slow" if it attains maximum after 0.4 of its lifetime. About 75 per cent of all flares are fast. But very slow flares of low intensity do occur. A region has been called "recurrent" if 5 or more distinct flares are observed there at one station in one transit of the disk or if 10 or more have been reported by all co-operating obseryatories. Recurrent regions are most often in or near spot groups of complex magnetic polarity ( and groups). Although flares are least likely to occur over stable unipolar groups, there are recurrent regions in the Quarterly Bulletins that were associated with groups predominantly unipolar. In the Quarterly Bulletins the active regions are given a new number at each rotation, regardless of whether a region appeared at preceding rotations. When the results are reduced to individual active regions, it was found that 159 such regions over which recurrent flares appeared produced 4187 of the 8056 flares recorded from October, 1935, to December, 1949. That is, 159 individual active regions, which constituted 12 per cent of the whole number of 1371, produced 52 per cent of the flares. Occasionally a flare appears abnormally bright for several hours or even days with only minor changes in form and intensity. Such flares have been called "persistent." An interesting example is described which was apparently the cause of exceptionally intense reception on the 80 Mc/sec band. The name of "flash" has been g\ to weak flares with a duration of 5 minutes or less. Some flash flares may possibly be prominence surges" seen on the disk. Owing to difficulties of observation, the flash flares may be more numerous than we suppose and may possibly make a considerable contribution to the solar ultraviolet radiation. Flares of intensity 3 $ have been called "superflares." About 70 per cent are associated with spot groups of complex magnetic polarity. A comparison of complex groups and simple bipolar groups of the same area shows that the number of flares over the complex groups is always greater. The question has been investigated of whether two or more flares occur nearly simultaneously oyer widely separated spot groups more often than would be expected by chance. The number of multiple flares observed was found to be higher than the number calculated, if they occurred at random, from Poisson's law. It is felt, however, that a definite conclusion cannot be drawn until data are available for another cycle. The total emission from the flare of February 21, 1950, at maximum intensity in the K line was found by photographic photometry to be 3.2 X 10 erg/sec. The radiation from the hemisphere of the sun at 6000 K in the same width of neighboring spectrum is 1395 X 1026 erg/sec. Publication: The Astrophysical Journal Pub Date: September 1951 DOI: 10.1086/145473 Bibcode: 1951ApJ...114..356R full text sources ADS |
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