Variation of Thermal Structure with Height of a Solar Active Region Derived from SOHO CDS and YOHKOH BCS Observations

Details Variation of Thermal Structure with Height of a Solar Active Region Derived from SOHO CDS and YOHKOH BCS Observations Variation of Thermal Structure with Height of a Solar Active Region Derived from SOHO CDS and YOHKOH BCS Observations

Oct 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...524.1096s&link_type=abstract

The Astrophysical Journal, Volume 524, Issue 2, pp. 1096-1104.

Astronomy and Astrophysics

Astronomy

8

Sun: Corona, Sun: Uv Radiation, Sun: X-Rays, Gamma Rays

Scientific paper

We present observations of NOAA solar Active Region 7999 when it was near the west solar limb on 1996 December 2 and 3, using data from the Coronal Diagnostic Spectrometer (CDS) experiment on the SOHO satellite. Ratios of intensities of 2 MK material (as observed in CDS Fe XVI images) to 1 MK material (from CDS Mg IX images) indicate that there is a drop in the ratio of the hotter to the cooler material with height in the region, up to an altitude of about 10^5 km. At low altitudes the relative amount of 2 MK emission measure to 1 MK emission measure ranges from 8 to 10, while the ratio is minimum near 10^5 km, ranging from 1.3 to 3.5. The decrease with height of the CDS ratio qualitatively resembles the decrease in S XV election temperature with height (measurable up to ~85,000 km) in the same active region obtained from the Bragg crystal spectrometer instrument on Yohkoh. The CDS images indicate that the highest S XV temperatures and largest CDS ratios correspond to regions of microflares, and somewhat lower S XV temperatures and CDS ratios correspond to diffuse regions. Above 10^5 km, the trend of the CDS ratios changes, either increasing or remaining approximately constant with height. At these altitudes the CDS images show faint, large-scale diffuse structures.

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