Is the solar 5 min oscillation an important heating mechanism for the chromosphere and the corona?
✍ Scribed by Peter Ulmschneider
- Publisher
- Springer
- Year
- 1976
- Tongue
- English
- Weight
- 233 KB
- Volume
- 49
- Category
- Article
- ISSN
- 0038-0938
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✦ Synopsis
Missing power in the spectrum of intensity fluctuations of both XUV and radio emission in the transition layer and inner corona as well as the 90 ~ phase shift between intensity and velocity fluctuations in the chromosphere indicate that the 5 rain oscillation transports little energy and is not a significant mechanical heat source for the chromosphere and possibly not even for the corona.
Recently the mechanism of the 5 min oscillation in the solar photosphere and chromosphere has become increasingly clear. Observations of high temporal and spatial resolution by Deubner (1976a, b) reveal a ridgy structure of the power of velocity oscillations in a frequency w, wave number k diagram. These ridges are produced by nonradial pulsations of the solar envelope Ulrich (1970), Wolff (1972), Ando and Osaki (1975). Here any particular ridge represents pulsations of a fixed number of nodes in radial, but different number of nodes in angular direction. Only those modes are observed that are overstable, that is, whose amplitudes are found to grow with time. Because overstability is thus a significant generation mechanism for acoustic waves in the band around 5 min, it is competive with the Lighthill mechanism and the possible penetrative convection mechanism (Stein and Leibacher, 1974). It is of great importance to find out which of these mechanisms is significant energetically for the heating of the chromosphere and the corona. For this purpose we base our arguments largely on observations for which Beckers (1976) gave a convenient summary.
The penetrative convection mechanism is thought to generate gravity waves near the temperature minimum region where radiative damping becomes unimportant. However very little power has been found in the region of the ~o, k diagram where gravity waves should be seen (Deubner, 1974). Therefore the penetrative convection mechanism seems to generate little energy.
The amount of energy generated by the overstability mechanism in the 5 min oscillation likewise seems to be quite low. This is indicated by the very weak power of the 5 min oscillation in the intensity fluctuations of the mm and cm radio emission of the transition layer and inner corona (Yudin