Brightness distribution at the base of a coronal hole |
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| Authors: | R B Teplitskaya O A Ozhogina I P Turova |
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| Institution: | (1) Institute of Solar-Terrestrial Physics, Russian Academy of Sciences, Siberian Branch, P.O. Box 4026, Irkutsk, 664033, Russia |
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| Abstract: | A coronal hole was observed for three days of its passage near the central meridian of the Sun. Spectrograms containing strong lines of ionized calcium were obtained. The central intensities of the Ca II H, K, and λ849.8 nm lines in the region of the coronal hole and in the quiet-Sun region outside its boundaries were measured. Only the line profiles that were confidently identified as being undisturbed even by weak flocculi were selected. All profiles were averaged in each of the two chromospheric network components (network and cell), and the average profiles were calculated using all of the available data (network+cell). Small differences were found between the central intensities of the Ca II H and K lines inside and outside the coronal hole, with the hole being brighter than the quiet region. A detailed statistical analysis shows that these small differences are real at high confidence levels owing to the large sample sizes. A difference of the same sign is slightly noticeable in the infrared line, but its confidence level is less than 90%. The chromosphere in the coronal hole is brightened by the cell alone; in the network, the chromospheric foot of the coronal hole does not differ from the quiet region. Comparison with the results of other authors obtained from observations in higher atmospheric layers suggests that the network also contains a brightness peak that subsequently gives way to a characteristic depression, but it lies higher than that in the cell. |
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