8 research outputs found
SUMER Observations Confirm the Dynamic Nature of the Quiet Solar Outer Atmosphere: The Inter-network Chromosphere
On 12 March 1996 we obtained observations of the quiet Sun with the SUMER
instrument. The observa- tions 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. 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". At any time they occur over
approx. 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 (lambda > 912 A) 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. Three minute intensity
oscillations are occasionally seen in second spectra (C II 1335), but never in
third spectra (C III and Si III). Third spectra and He I 584 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 data show that time variations are crucial for our
understanding of the chromosphere itself and for the spectral features formed
there.Comment: 8 pages, 3 figs, AASTeX, Accepted for publication in APJ letter