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K. Wilhelm (Max-Planck-Institut für Aeronomie)
The structure and the dynamics of the solar chromosphere are still a matter of scientific debate. In particular, the physics of the so-called nonmagnetic chromosphere in cell regions of the network structure is not yet fully understood. Here we present SUMER observations of the H\,{\sc i} Lyman continuum obtained in areas of the undisturbed Sun in November 1996. The sequences are unique in the sense that the spectral range from 75~nm to 79~nm is sampled several times with a cadence of 30~s for 390~s, which is near the limit of the telemetry and memory capabilities of the instrument. In this wavelength range not only the Lyman continuum, but also many EUV emission lines (N\,{\sc ii}, N\,{\sc iii}, S\,{\sc iv}, O\,{\sc iv}, O\,{\sc v}, and Ne\,{\sc viii}) are prominent, allowing us to investigate radiation formed at temperatures representative of regions from the chromosphere to the corona. Several brightenings can be identified which are assumed to be related to the well-known three-minute brightenings observed, for instance, in the Ca\,{\sc ii} line. The fractional variation of the continuum radiance was up to 40~%, whereas simultaneously recorded transition region lines varied by about 60~%. The Ne\,{\sc viii} lines with a formation temperature of 620\,000~K showed relative changes of less than 14~% and displayed no phase relationship with the transition region lines or the continuum. We will discuss SUMER observations with a view towards providing constraints for modeling chromospheric dynamics and structure.
The author(s) of this abstract have provided an email address for comments about the abstract: wilhelm@linmpi.mpg.de
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.