Center limb observations of inhomogeneities in the solar atmosphere

✍ Scribed by C. J. Cannon; P. R. Wilson

• Publisher: Springer
• Year: 1971
• Tongue: English
• Weight: 899 KB
• Volume: 17
• Category: Article
• ISSN: 0038-0938
• DOI: 10.1007/bf00150033

✦ Synopsis

Center-limb observations of line-center intensity fluctuations in the Na D and Na 5688 doublets and the Mg 4571 line are described. For small scale structures the rms distributions for the photospheric lines show maxima of 20% at a heliocentric angle of 40 ~ (Mg 4571) and 9% at 20 ~ (Na 5688). The rms values for Na D range between 10 and 13 % but show no significant maximum. Values for large scale structures are somewhat less.

Auto-correlation curves show a range of structures from 4000 km to 30000 kin. Brightnessvelocity cross-correlation curves and the actual brightness and velocity tracings from a region near disk-center are also studied. A new method of classifying cross-correlation coefficients calculated over many different ranges within the sample enables one to distinguish the existence and extent of regions of significant cross-correlation within the sample and this is applied both to the results for the Na D lines and for the Mg b lines given in Paper I. It is found that regions of significant correlation may extend for lengths of order 25000 krn after which the correlation may abruptly change sign or become negligible. The suggestion made in Paper I that these abrupt changes may occur at the supergranule boundaries is further supported.

The relation between these small scale structures and the 5 rain oscillations is investigated. The question of the reproducibility of these statistical data from day to day and at different positions of the Sun at the same heliocentric angle is discussed and the need for further independent observations is stressed.