1. SECCHI Deputy Program Manager
The Solar EUV Monitor on SOHO (CELIAS/SEM)
Donald R. McMullin
SECCHI Deputy Program Manager
NRL / Praxis, Inc.
June 21, 2006
Bern, Switzerland

2. Acknowledgements
Darrell L. Judge, Howard Ogawa, Andrew Jones, Matt Harmon
SOHO/SEM Data
USC Space Sciences Center
SOHO/SEM data available at:

3. SEM = > LYRA Al channel
Overview
Introduction to the SOHO/SEM Instrument
Data examples
Calibration monitoring and comparisons
EUV and X-ray flares observed by SEM
Time cadence of SEM observations
Conclusions
SEM = > LYRA Al channel

4. History of EUV Measurements
Many long gaps with little or no data
Never a continuous measurement over a solar cycle – Until CELIAS/SEM
CELIAS/SEM
Wavelength (nm)
OSO AEROS AE-E SM5
Year

5. Solar EUV Monitor (SEM)
Components
1 Transmission Grating
1 Aluminum Filter
3 Aluminum coated diodes
3 science channels:
1 central image (0.1-50nm)
2 first order 30.4 nm (26-34nm)

6. SEM

7. 27 day periodic features observed throughout the dataset
Minimum EUV flux 3/10/96

8. In-Flight Monitoring 3 Underflight Sounding Rocket Missions SEM Clone
Rare Gas Ionization Cell
36.147US June 26, 1996
36.164US August 11, 1997
36.181US August 18, 1999

10. CELIAS/SEM FOC comparison to Mg II Index
Note: Excellent agreement throughout the data set
"The Mg II Index: A Proxy for Solar EUV," submitted to GRL, 2000, R. Viereck, D.R. McMullin, L. Puga, W.K. Tobiska, M. Webber, D.L. Judge.
R. Viereck, NOAA SEC

11. Photoionization rates are calculated by folding the measured solar EUV irradiances into theoretical or laboratory measured photoionization cross sections.
The defining rate equation is applicable within an optically thin medium.
This method was employed by Banks and Kockarts [1973], Torr et al.[1979], and Torr and Torr [1985]

12. Helium Photoionization rate derived from CELIAS/SEM absolute EUV flux
Jan 1, 1996 through Jan 31, 2001

13. The Solar EUV Hitchhiker (SEH)
Helium Double Ionization Cell
Rare Gas Ionization Cell
NIST secondary transfer standard diodes
EUV spectrometer
Direct measurements of the helium photoionization rate from the Space Shuttle
Mission Launch Date
STS Sep. 1995
STS August 1997
STS October 1998

14. Historical comparison of Helium Photoionization rate values with the SEM-MgII Rate Proxy

15. Looking at x-rays in SEM data

16. 5 minute SEM data DOY

17. Here are some examples of solar flares observed by the SEM
Here are some examples of solar flares observed by the SEM. Both EUV and x-ray channels are shown at 5 minute time cadence.

19. Looking at SEM high time cadence

20. Looking at SEM high time cadence
SEM is limited by quantization (compression), not solar noise.

21. Conclusions SEM is a good candidate for LYRA Al channel comparisons.
LYRA can provide new information for SEM time cadence studies.
As is usual, calibrations may be a topic of future discussions.
SEM data is now available on web or by .