Oscillations of the upper chromosphere

TitreOscillations of the upper chromosphere
Type de publicationJournal Article
Year of Publication1999
AuteursGouttebroze, P., Vial J.-C., Bocchialini K., Lemaire P., and Leibacher J. W.
JournalSolar Physics
Date PublishedFeb

Variations of intensity and wavelength in several UV lines have been observed with the SUMER spectroheliometer onboard SOHO, and they have been analysed to obtain oscillation spectra and phase differences between lines of different ions. Lines intensities of neutral or singly ionized atoms (with temperature of formation łt}=30000K) exhibit an increase of oscillatory power between 2.5 and 7mHz, which may be considered as the signature of pmodes. Lines of highly ionized elements (with a temperature of formation {\gt}=50000K) yield power spectra which are continuously decreasing with frequency. Brightness variations of the continuum at different wavelengths between 1000 and 1400Å present oscillations in the same frequency range. Thus, pmodes seem to be efficiently stopped by the transition region. No clear evidence is found for the existence of a chromospheric oscillation mode. Phase comparisons between lines formed at different altitudes (in particular Sii and Siii) indicate that these lines oscillate in phase, within the precision of the measurements.