Resonant oscillations in sunspot umbrae

Details Resonant oscillations in sunspot umbrae Resonant oscillations in sunspot umbrae

Aug 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990soph..128..353w&link_type=abstract

Solar Physics (ISSN 0038-0938), vol. 128, Aug. 1990, p. 353-364.

Physics

12

Solar Atmosphere, Solar Oscillations, Sunspots, Umbras, Gravity Waves, Magnetic Flux, Magnetoacoustic Waves, Resonant Vibration

Scientific paper

The Uchida and Sakurai (1975), Thomas and Scheuer (1982), and Scheuer and Thomas (1981) theory of umbral oscillations as resonant modes of magnetoacoustic-gravity waves is reexamined. For an isothermal atmosphere it is found that the quasi-Alfven approximation is not a good approximation to the complete linearized wave equations. The new results presented here show that 3-min umbral oscillation periods are fairly insensitive to magnetic field strength above some critical value. For a detailed model umbra, the calculations presented here show that 3-min umbral oscillations do not depend to any great extent on the level of forcing of the oscillations for those magnetic field strengths which are observed in sunspot umbras. Models outside the 3-min range appear, as the lowest mode, as the level of forcing is placed at deeper and deeper levels in the solar atmosphere.

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