Oscillations in the solar atmosphere - The 5-min peak as a consequence of wave reflection at the photosphere

Details Oscillations in the solar atmosphere - The 5-min peak as a consequence of wave reflection at the photosphere Oscillations in the solar atmosphere - The 5-min peak as a consequence of wave reflection at the photosphere

Aug 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991mnras.251..427w&link_type=abstract

Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 251, Aug. 1, 1991, p. 427-437.

Astronomy and Astrophysics

Astronomy

11

Photosphere, Solar Oscillations, Reflected Waves, Solar Atmosphere, Solar Spectra

Scientific paper

Consideration is given to the vertical propagation of compression waves from beneath the solar atmosphere. It is shown that at the step-up in critical frequency which occurs at the photosphere, the phase difference between reflected and incident waves depends greatly on frequency, and is zero at about 3 mHz. This is argued as the reason why velocity power spectra deduced from photospheric lines have maxima at that frequency (period 5 min), if all modes are excited to equal velocity amplitudes, i.e., to equal higher density, in the region just beneath the photosphere. Higher in the atmosphere, standing-wave components can be set up at frequencies higher than the top of the barrier, which is about 4.5 mHz. The first of these has a period of about 200 s, and may be responsible for the peak observed at that period in power spectra from chromospheric spectral lines. For waves of frequency higher than 4.5 mHz, the relatively cool layer between the photosphere and corona acts as an acoustic interference filter which is most transparent at those frequencies at which standing waves are set up within it.

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