Solar flares and associated 1.5 meter radiation.

Abstract

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Solar flares and associated 1.5 meter radiation. Dodson, Helen W. ; Hedeman, E. Ruth ; Owren, Leif Abstract The McMath-Hulbert Observatory of the University of Michigan and the School of Electrical Engineering of Cornell University have for the last year and three-quarters conducted a cooperative program in which the goal has been the detailed comparison, hour by hour, of the solar radio radiations at 1.5 meters with solar activity observed photographically and visually. Different solar phenomena apparently influence the 1.5 meter records, but it is for solar flares that the relationships are most clear cut. This study is based principally on those flares for which complete photographic records are available at the McMath-Hulbert Observatory, but it has been extended to include data reported by the International Astronomical Union and the Central Radio Propagation Laboratory of the National Bureau of Standards. Between the start of the Cornell Radio records on July 18, 1948 and December 31, 1950, there are 141 flares for which the optical and radio data permit definitive comparison. It should be emphasized that a solar flare is a * On leave of absence from Institute of Theoretical Astrophysics, University of Oslo. complex phenomenon and that the aspect of the flare that is related to the response at 1.5 meters is not certain. The complexity of the flare phenomenon becomes clear when it is realized that in addition to the usually observed sudden brightening in Ha there may or may not be (I) an ultraviolet component of sufficient intensity to cause a sudden ionospheric disturbance on the earth, (2) a spreading of a low grade brightening to relatively distant parts of the plage in the later stages of the flare, (3) active dark flocculi or surges in projection on the disk, (4) the actual ejection of material particles. The 200 Mc$sec response to flares shows a wide range in both magnitude and kind. These responses can be divided into seven descriptive categories or types. I) Major bursts (including the group known as outbursts); (22 cases). 2) Minor bursts; (22 cases). 3) Micro bursts; (6 cases). 4) Series of bursts; (32 cases). 5) Small rise in base level; (4 cases). 6) Noise storms; (26 cases). 7) Nulls; (29 cases). Eighty per cent of the flares produced some form of energy excess on the 1.5 meter records. For 25 of the 29 flares for which there was no distinctive radio response the associated solar phenomena were relatively unimportauf. For at least 4 cases, however, the flares were of importance 2 or more. The energy excess represented by the flare response at 1.5 meters has been measured for 20 flares. For these cases there appears to be a direct relationship between the importance of the flare and the energy excess associated with it. Comparisons of the times of onset of the optical flare and the radio response indicate that the major, minor, and micro-bursts tend to occur at the very commencement of the optical rise. The series of bursts begin before the observer detects the start of the flare in Ha radiation. On the other hand, many of the noise storms and rises in base level have their onset at or near flare maximum. These delayed responses increase in intensity as the flare fades and often attain their greatest intensity just as the optical flare has faded completely. McMath-Hulbert Observatory, University of Michigan, Pontiac, Mich., and School of Electrical Engsneersng, Cornell University, Ithaca, N. Y. Publication: The Astronomical Journal Pub Date: April 1952 DOI: 10.1086/106783 Bibcode: 1952AJ.....57R...9D full text sources ADS |