Evolution of coronal regions.

Abstract

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Evolution of coronal regions. Billings, D. E. ; Liebenberg, D. H. ; Roberts, W. O. Abstract The authors have examined the behavior of regions in the solar corona near sunspot groups, which show intense coronal line emission. The results led them to formulate the following working hypothesis of the origin of the emission line corona. I. Yellow, red and green line emission at XX 5694, 6374 and 5303 in a coronal region becomes pronounced with infusion into the corona of gas of density considerably higher than that of the corona prior to the infusion. 2. The infusion takes place most strongly from active sunspot centers during their periods of flare activity. 3. The gas spreads out through the corona along magnetic lines of force at about I km/sec, at a sufficient rate to replace the entire emission corona in the order of a few weeks. 4. As the gas spreads out, its temperature rises slowly. 5. Resulting temperature and density conditions are such that yellow line emission persists for several hours, red line emission for a few days, green line emission for about a week or two. 6. The coronal region drops below a recognizable level of brightness as the gas expands to a low density, but before the return to normal in its temperature. This concept, arrived at from a study of coronagraphic data, agrees with that suggested by Piddington and Davies from solar radio noise observations.1 The principal observational data which led to the concept are: A. The close association of coronal emission and flare activity. B. The spreading out of isophotal contours of coronal emission at a rate of about 2' km/ sec during the growth of the coronal region and sometimes after the sunspot and flare activity at the center has subsided. This slow spread is perhaps related to the behavior of the "disparitions brusques" reported by Bruzek following solar flares.2 C. Many cases of a unidirectional change of the ratio of red line to green line emission, usually downward, during a rise and fall of brightness of coronal regions. We see no way to explain this last observation by the hypothesis that coronal regions differ from the remainder of the corona only in that they are of higher temperature. We can, however, explain it by the spreading gas hypothesis. This work was carried out with the support of the Office of Naval Research. I.Nature 171, 692, 1953. 2.Zs. Astroph. 31, 99, 1952. High Altitude Observatory, Boulder, Cob., and University of Wisconsin, * Madison, Wis. Publication: The Astronomical Journal Pub Date: 1953 DOI: 10.1086/106934 Bibcode: 1953AJ.....58S.211B full text sources ADS |