Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983a%26a...123..263u&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 123, no. 2, July 1983, p. 263-270. Sponsorship: Deutsche Forschungsgemeinschaf
Astronomy and Astrophysics
Astrophysics
37
Chromosphere, Solar Oscillations, Sunspots, Umbras, Solar Spectra
Scientific paper
An analysis is made of time sequences of photographic spectrograms in Ca II H, K, 8498 A, and 8542 A, in sodium D1 and D2, and in Ni I 5893 A and H-alpha obtained from two sunspots with the Vacuum Tower Telescope at Sacramento Peak Observatory. The two sunspot chromospheres are found to behave similarly with regard to their phase relationships but somewhat differently with regard to the oscillation resonant frequencies. In one and the same umbra, oscillation modes having different frequencies may be excited. The vertical velocity of propagation of the phase in umbral chromospheres, which is 10-25 km/s, decreases with increasing frequency and is much lower than the Alfven speed. The umbral chromospheric oscillations are thus slow mode waves. The downward motion enhances the intensity by some 65 deg (H-alpha) to 85 deg (D1), indicating dissipation of mechanical energy. It is also found that the mechanical energy flux of the umbral chromospheric oscillations is not sufficient to account for the chromospheric radiative losses.
Kneer Franz
Mattig Wolfgang
Uexkuell M. V.
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