34th Solar Physics Division Meeting, June 2003
Session 4 Corona II
Poster, Monday, June 16, 2003, 3:30-5:00pm, Mezzanine

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[4.01] Sunspot Oscillations and Acoustic Wave Propagation

P. Brekke (European Space Agency), N. Brynildsen, P. Maltby, T. Fredvik, O. Kjeldseth-Moe (Institute of Theoretical Astrophysics)

Observations with the Coronal Diagnostic Spectrometer of 3 min oscillations in sunspot umbrae support the hypothesis that they are caused by upwardly propagating acoustic waves. This is evident from the asymmetry of oscillation amplitudes in the red and blue wings of spectral lines, where the oscillations are decidedly more pronounced in the blue than in the red line wing. Additional evidence include the fact that the relation between oscillations in intensity and velocity agree with that predicted for an acoustic wave with regard to phase as well as magnitude. Finally, the observed phase difference between lines formed at different temperatures points to an upward propagating disturbance, and the value of dominant frequency of the oscillations, close to 6 mHz, is above the acoustic cutoff frequency in the sunspot atmosphere. SOHO is a mission of international cooperation between ESA and NASA. This study was supported by the Research Council of Norway.

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