1. NAM and UKSTP 11 April 2003 Sensitivity Differences in Pre-Loss and Post-Recovery NIS/CDS Spectrum By Steven Chapman Centre for Astrophysics University of Central Lancashire

2. NAM and UKSTP 11 April 2003 Contents Background on the side effects of the recovery of SoHO concerning CDS/NIS The Synoptic data Determining the modal low-emission intensity and showing the variation Aligning the pre-loss and post-recovery low-emission intensities Conclusion Aligning higher intensities

3. NAM and UKSTP 11 April 2003 Background… My main area of work has been studying the variation of the coronal hole area over cycle 23, with the CDS/NIS synoptic study. This will be combined with magnetic flux data to show how the open flux varies. This has involved contouring low-emission regions, but to do this you need a cut-off level between the low-emission region and the quiet sun.

4. NAM and UKSTP 11 April 2003 What Changed After the Recovery? The spectral line profiles of the NIS-1 and NIS-2 had acquired substantial wings on either side of the line. The sensitivity of the NIS-1 instrument has been noticeably reduced. NIS-2 sensitivity appears to be unaffected. CDS Software Note 53

5. NAM and UKSTP 11 April 2003 Pre-Loss and Post-Recovery Line profiles of Mg IX and Mg VII (NIS-1)

6. NAM and UKSTP 11 April 2003 Synoptic Data SoHO CDS Synoptic data is a long, near continuous data set. This is ideal to study changes in the behaviour of the CDS/NIS instrument Covers 5 lines in EUV wavelengths – He I, Fe XVI, Mg IX, Mg X (added in May 1998) and O V. The meridian of the Sun is covered by 9 rasters. Each raster is a cube of data. A 2D image where each pixel is made up of a spectrum of the mentioned lines.

7. NAM and UKSTP 11 April 2003 22 May 1998 - EIT 195Å Full Disk of the Sun, with CDS synoptic pointings of all nine rasters overlaid

8. NAM and UKSTP 11 April 2003 22 May 1998 Mg IX Meridian Strip IntensityContoured Low-Emission Extracted Low-Emission

9. NAM and UKSTP 11 April 2003 Finding the Modal Low-Emission Intensity Histograms of all the masked pixels intensities are created. The peak shows the most common low-emission intensity for each masked image.

10. NAM and UKSTP 11 April 2003 Variation of the Modal Low-Emission Intensity, Uncorrected

11. NAM and UKSTP 11 April 2003 Aligning the Post-Recovery Low-Emission Intensities, Correction = 1.45

12. NAM and UKSTP 11 April 2003 Aligning the Post-Recovery Low-Emission Intensities, Correction = 1.8

13. NAM and UKSTP 11 April 2003 Aligning the Post-Recovery Low-Emission Intensities, Correction = 2.2

14. NAM and UKSTP 11 April 2003 Conclusion The sensitivity of the NIS1 instrument has been affected by the temporary loss of SoHO. The post-recovery low-emission intensities need a correction factor of ~1.8 to align it with the pre-loss. This investigation has only been done with ~300 days of data. Work is currently being done in studying all of the CDS synoptic data, to determine an acceptable low-emission correction factor for post-recovery NIS-1 data.

15. NAM and UKSTP 11 April 2003 Preliminary Investigation into Other Intensity Levels Early results in aligning post-recovery to pre-loss intensity levels shows that a non-constant correction factor is needed. Masked images have been created with a Mg X image using the following intensity level bands. These have been overlaid with the corresponding Mg IX image and then the pre and post intensity levels have been aligned. 0.00.07 (Coronal Hole) 0.070.4 0.50.6 (Quiet Sun) 0.70.8 0.8∞ (Active Region) (intensity units – photons-events/sec/pixel)

16. NAM and UKSTP 11 April 2003 A Non-Constant Correction Factor