Chromospheric Oscillations Observed with OSO 8. II. Average Phase Spectra for SI II.

Details Chromospheric Oscillations Observed with OSO 8. II. Average Phase Spectra for SI II. Chromospheric Oscillations Observed with OSO 8. II. Average Phase Spectra for SI II.

Mar 1979

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979apjs...39..347w&link_type=abstract

Astrophysical Journal Supplement Series, vol. 39, Mar. 1979, p. 347-358.

Computer Science

Sound

24

Scientific paper

Time series of intensity and Doppler-shift fluctuations in the Si II emission lines λ1816.93 and λ1817.45 are Fourier analyzed to determine the frequency variation of phase differences between intensity and velocity and between these two lines formed 300 km apart in the middle chromosphere. Average phase spectra show that oscillations between 2 and 9 mHz in the two lines have time delays from 35 to 40s, which is consistent with the upward propagation of sound waves at 8. 7.5 km s-1. In this same frequency band near 3 mHz, maximum brightness leads maximum blueshift by 600. At frequencies above 11 mHz where the power spectrum is flat, the phase differences are uncertain, but approximately 65% of the cases indicate upward propagation. At these higher frequencies, the phase lead between intensity and blue Doppler shift ranges from 0° to 180° with an average value of 90°. However, the phase estimates in this upper band are corrupted by both aliasing and randomness inherent to the measured signals. Phase differences in the two narrow spectral features seen at 10.5 and 27 mHz in the power spectra are shown to be consistent with properties expected for aliases of the wheel rotation rate of the spacecraft wheel section.

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