EUV SPECTROSCOPY OF THE SUNSPOT REGION NOAA 7981 USING SOHO: I. Line Emission and Time Dependence

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Abstract

EUV spectra of a medium-size sunspot and its surroundings, NOAA 7981, were obtained on 2 August 1996 with the Coronal Diagnostic Spectrometer (CDS) and the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) on the Solar and Heliospheric Observatory (SOHO). The spectral lines formed in the transition region and corona show considerable structure and large deviations from a uniform spatial distribution over the active region. Enhanced EUV emissions in transition region lines are concentrated in small regions outside the umbra of the sunspot throughout most of the observing sequence. Only during a short, active period do we find an enhanced line emission that reaches into the umbra. Preliminary values for the umbral intensity are given.

Marked changes are detected between the spatial distribution of line emission in the transition region and the low corona. The difference is not limited to cool and hot non-flaring loops not being cospatial, but includes differences both regarding the time variability and the orientation and size of the emission features. Whereas both rapid (≈ 4 and 2 min) and slow (≈ 10 and 12 h) temporal variations are found in the chromosphere (Hei 584 Å) and transition region (Ov 629 Å), the response in the low corona (Mgix 368 Å) is slow (≈ 5 h). Furthermore, marked differences between the spatial distributions in the Mgviii 315 Å, Mgix 368 Å lines formed in the low corona and the coronal Fexiv 334 Å, Fexvi 360 Å lines are detected.

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