Electronic Resource
Springer
Solar physics
88 (1983), S. 275-280
ISSN:
1573-093X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Physics
Notes:
Abstract We derive an occurrence frequency for white-light flares (WLF) of 15.5 ± 4.5 yr−1 during a 2.6 year period following the maximum of solar cycle 21. This compares with a frequency 5–6 yr−1 derived by McIntosh and Donnelly (1972) during solar cycle 20. We find that the higher frequency of the more recently observed WLFs is due to the availability of patrol data at shorter wavelengths (λ ≲ 4000 Å), where the contrast of the flare emission is increased; the improved contrast has allowed less energetic (and hence more frequently occurring) events to be classified as WLFs. We find that sufficient conditions for the occurrence of a WLF are: active region magnetic class = delta; sunspot penumbra class = K, with spot group area ≥ 500 millionths of the solar hemisphere; 1–8 Å X-ray burst class ≥ X2.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00196192
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