SUMER Observations Confirm the Dynamic Nature of the Quiet Solar Outer Atmosphere: The Inter-network Chromosphere

On 12 March 1996, during the commissioning phase of the SOHO mission, we obtained observations of the quiet Sun with the SUMER instrument. The observations were sequences of 15-20 second exposures of ultraviolet emission line profiles and of the neighboring continua. These data contain signatures of the dynamics of the solar chromosphere that are uniquely useful because of wavelength coverage, moderate signal-to-noise ratios, and image stability. We focus on data for the inter-network chromosphere. The dominant observed phenomenon is an oscillatory behavior that is analogous to the 3 minute oscillations seen in Ca II lines. The oscillations appear to be coherent over 3-8 arcsecond diameter areas. At any time they occur over ∼50% of the area studied, and they appear as large perturbations in the intensities of lines and continua. The oscillations are most clearly seen in intensity variations in the UV (λ > 912Å) continua, and they are also seen in the intensities and velocities of chromospheric lines of C I, N I and O I. Intensity brightenings are accompanied by blueshifts of typically 5 km s. Phase differences between continuum and line intensities also indicate the presence of upward propagating waves. The detailed behavior is different between different lines, sometimes showing phase lags. Three minute intensity oscillations are occasionally seen in second spectra (C II λ1335), but never in third spectra (C III and Si III). Third spectra and He I λ584 show oscillations in velocity that are not simply related to the 3 minute oscillations. The continuum intensity variations are consistent with recent simulations of chromospheric dynamics (Carlsson & Stein 1994) while the line observations indicate that important ingredients are missing at higher layers in the simulations. The National Center for Atmospheric Research is sponsored by the National Science Foundation