Photospheric oscillations. II - Acoustic filtering in the solar atmosphere and heating of the chromosphere

Details Photospheric oscillations. II - Acoustic filtering in the solar atmosphere and heating of the chromosphere Photospheric oscillations. II - Acoustic filtering in the solar atmosphere and heating of the chromosphere

Oct 1975

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1975a%26a....43..253f&link_type=abstract

Astronomy and Astrophysics, vol. 43, no. 2, Oct. 1975, p. 253-257.

Astronomy and Astrophysics

Astrophysics

9

Fraunhofer Lines, Optical Resonance, Photosphere, Power Spectra, Spectrum Analysis, Acoustic Propagation, Calibrating, Chromosphere, Filters, Fourier Analysis, Modal Response, Normal Density Functions, Solar Spectra, Time Series Analysis

Scientific paper

Summary. Intensity fluctuations in the wings of the Fraunhofer line Na D t 5896 have been recorded for about two hundred hours at the focus of the Nice coude' refractor, using a sodium optical resonance device. Because of the large beam aperture available, records have been made on circular apertures from 22" up to 32' diameter (the whole sun). The principal results from the analysis of these data are: - As shown by White and Cha (t973), the five-minute oscillation has a gaussian random character with a mean lifetime of about 20 min. Its two-dimensional spatial power spectrum is roughly gaussian for every temporal frequency between 2 and 6 MHz. The width of this gaussian spectrum is near 5 t0- km -1 (i.e. 2 = 20000 km). It is shown that this value corresponds to a cellular pattern having a "coherence scale" near 5000 km. Various results published since 1962 concerning this coherence scale become consistent by taking a unified definition of this scale. - A new oscillatory mode of to min period has been discovered, for photo spheric apertures larger than 3' It does not appear to have the random gaussian character of the 5-min mode, but seems to be a spasmodical phenomenon, both in space and time. Key words: optical resonance photo spheric oscillations

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