Chromospheric and transition region internetwork oscillations: A signatureof upward-propagating waves

We analyze spectral time series obtained on 1997 April 25 with the SUMER in strument on SOHO. Line and continuum data near 1037 Angstrom were acquired at a cadence of 16 s. This spectral region was chosen because it contains s trong emission lines of C II, formed in the upper chromosphere/lower transi tion region,: O VI, formed in the upper transition region; and neighboring continuum emission formed in the middle chromosphere. The time series revea l oscillatory behavior. Subsonic (3-5 km s(-1) amplitude) Doppler velocity oscillations in the C II and O VI lines, with periods between 120 and 200 s , are prominent. They are seen as large-scale coherent oscillations, typica lly of 3-7 Mm length scale, occasionally approaching 15 Mm, visible most cl early in internetwork regions. The Doppler velocity oscillations are relate d to oscillations seen in the continuum intensity, which precede upward vel ocity in C Ir by 40-60 s. The C II Doppler shift precedes the O VI Doppler shift by 3-10 s. Oscillations are also present in the line intensities, but the intensity amplitudes associated with the oscillations are small. The c ontinuum intensity precedes the C II intensity by 30-50 s. Phase difference analysis shows that there is a preponderance of upward-propagating waves i n the upper chromosphere that drive an oscillation in the transition region plasma, thus extending the evidence for upward-propagating waves from the photosphere up to the base of the corona.