Photometric studies of solar flares.

Abstract

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photometric studies of solar flares. Dodson, Helen W. ; McMath, Robert R. ; Hedeman, E. Ruth Abstract The development, at the McMath-Hulbert Observatory during 1950, of a new and improved densitometer for the measurement of intensities of features photographed on 35 mm motion picture film has permitted an extension of the study of the "light curves" of solar flares. The intensity of the flare is expressed in terms of the intensity of the adjacent undisturbed disk as recorded on Ha spectroheliograms taken with slits 0.4A wide. The study to date has included twenty-one flares photographed in 1949, eight of importance I, nine of importance 2, and four of importance 3. The intensities at maximum range from 1.6 to 5 times the intensity of the undisturbed Hot background. All flares in this study for which the intensity of the flare was greater than 3 times that of the background were accompanied by sudden ionospheric disturbances regardless of the location of the flare on the solar disk or the area of the disturbance. Sudden ionospheric disturbances were not restricted to association with only the largest and most intense flares. On August 22, 1949 a flare of importance I, ~~O from the center of the sun, was accompanied by a sudden ionospheric disturbance even though it covered only 51 millionths of the solar hemisphere and reached an intensity of only 2.4 at maximum. This flare occurred directly over two spots. Two flares that took place on November I, 1949 in the same plage area, about 400 from the center of the sun, present an interesting anomaly. The first flare began at 1637 U.T., reached intensity 2.4 at maximum and extended over 130 millionths of the solar hemisphere. It was accompanied by a sudden ionospheric disturbance. The second flare broke out in the same plage area at 1954 U.T. This flare was more intense (2.75), larger (376 millionths) and lasted for a longer time (66 minutes) but there is no report of a sudden ionospheric disturbance for the period of its occurrence. Although both flares took place in the same plage area and between the same two large spots, the detailed regions involved in the two flares did not coincide or overlap in any way. The light curves of the flares make possible not only a study of the role of the maximum intensity in flare effects, but they also permit an investigation of the time relationships between the first indications of flare activity on the sun, the attainment of maximum intensity, the onset of the sudden ionospheric disturbance, and the relative durations of the solar and ionospheric phenomena. Although the work to date includes only a portion of the flares recorded in 1949, it is hoped that the photometric measures can be extended to include much of the large body of observational material secured during the recent solar maximum. MeMath-Hulbert Observatory, Lake A ngelus. Pontiac. Mich Publication: The Astronomical Journal Pub Date: April 1951 DOI: 10.1086/106486 Bibcode: 1951AJ.....56...37D full text sources ADS |