Five-minute oscillations of solar equivalent widths

Details Five-minute oscillations of solar equivalent widths Five-minute oscillations of solar equivalent widths

Aug 1975

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1975soph...43..271h&link_type=abstract

Solar Physics, vol. 43, Aug. 1975, p. 271-284.

Physics

10

Fraunhofer Lines, Periodic Variations, Solar Spectra, Spectral Line Width, Absorption Spectra, Decay Rates, Electrophotometry, Frequency Distribution, Noise Threshold, Power Spectra, Radiative Lifetime, Radiative Transfer

Scientific paper

Equivalent widths of weak and moderately strong Fraunhofer lines observed in an area roughly 3500 x 10,000 km in extent are found to show small variations of the order of 1 mA, on a time scale of minutes. The dependence of amplitude on line strength and excitation closely fits that predicted for a compressional disturbance associated with temperature variations that manifest themselves in the equivalent widths. These equivalent width variations frequently exhibit a 5-min periodicity and are accompanied by prominent oscillations of velocity. Power spectra of both quantities closely resemble each other and demonstrate that most of the equivalent width variations in the range 200 to 500 sec are due to the thermal response of the atmosphere to 5-min oscillations. A systematic phase lag between velocity and equivalent width is observed, in the sense that temperature leads velocity by an average angle of 120 deg. This deviates significantly from 90 deg valid for standing adiabatic waves, showing that in the line-forming layers, the 5-min oscillations are markedly affected by radiative exchange.

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