1. The EUV spectral irradiance of the Sun from minimum to maximum Giulio Del Zanna Department of Space and Climate Physics University College London Vincenzo Andretta INAF – OAC

2. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun Open questions What are the characteristics of the EUV irradiance? What are its long-term variations? Is the ‘quiet’ Sun constant in time? What is the relation between irradiance, magnetic activity and the various solar regions ? Can we use indices of activity to model the EUV irradiance ? Does the EUV irradiance affect the global climate ? SOHO (1996-2005) gives us the first opportunity to study EUV irradiances

3. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun Global warming Last 10 years probably the warmest in the last 8 000 years !

4. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun Global warming (Eddy 1976) "Winter Scene with Frozen Canal" by Aert van der Neer During the Little Ice Age, London’s Thames River froze in winter in the 17th Century, a very rare event. Solar activity (e.g. Sunspot number) correlates with many things (including temperature variations). But to what extent ?

5. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun Solar vs. anthropogenic and other (e.g. Volcanoes) effects (Lean 1997)

6. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun The total irradiance is one of the main drivers for global climate. Variability exists but is small (0.2%) and insufficient to explain variations on global weather. Fröhlich 2005, updated Fall 2004 AGU poster

7. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun The Solar spectrum (Floyd 2005) (Woods 2005) UV EUV

8. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun The EUV and UV UV radiation controls the amount of stratospheric ozone. UV variations could be a significant driver of changes in the terrestrial climate (e.g. Haigh 1996). The EUV radiation creates the ionosphere and might also have an indirect effect. (Lean 1997)

9. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun EUV `Hole’ (Floyd 1997) Very few EUV observations (below red line) until TIMED in 2002 The EUV irradiance has been modelled by using proxies (until 2002). The X-ray irradiance is still modelled.

10. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun TIMED: UV irradiance since 2002 (Woods et al 2005) Grey areas show the variability during 2002-2004 Variability increases toward the EUV

11. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun Variability in the X-rays Well known to be large Yohkoh SXT 1991 – 1995 ~100x change in x-ray brightness (Acton et al 1999). But SXT was a broad-band instrument.

12. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun Variability in the EUV from SOHO Solar EUV Monitor (SEM) … but SOHO/SEM produces broad-band count rates. We need EUV spectral irradiance to calibrate SOHO/SEM. How much is the contribution from the active regions?

13. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun The contribution from active regions seems dominant. There are no obvious long-term variations of the ‘quiet Sun’ at chromospheric levels Livingston, B. 2005, unpublished

14. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun OSO 3: Hall & Hinteregger (1970) The EUV spectrum is dominated by emission lines

15. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun With the SOHO/Coronal Diagnostic Spectrometer we observe the 15-80 nm region with the Normal Incidence (NIS) and Grazing Incidence (GIS) channels (9) NIS 2 GIS 3 NIS 1

16. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun SOHO/EIT vs. Magnetograms (SOHO/MDI)

17. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun GIS observations of the quiet Sun (1996-2005) At first we have obtained GIS radiances of the ‘quiet Sun’ during 1996-2003 and used SOHO/EIT to infer irradiances GIS spectra show a considerable increase in hotter lines

18. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun Histograms of the EIT intensity distributions

19. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun

20. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun EUV Irradiances from GIS

21. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun EUV Irradiances from GIS

22. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun EUV irradiances compared to previous records

23. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun NIS full-Sun spectra: 700-1000 single slit exposures sampling the whole Sun in 13 hours (1998-2005). See Thompson & Brekke (2000) for details. He I, He II

24. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun Transition region – O III, O V

25. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun Mg X – 1MK

26. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun Corona at 2-3 MK Si XII – Fe XVI

27. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun EUV Irradiances from NIS

28. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun EUV Irradiances from NIS compared to previous records

29. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun Conclusions The SOHO/ GIS, NIS have produced a valuable dataset (1996-2005) that allows, with the support of SOHO/EIT and atomic data (CHIANTI) to reconstruct the EUV spectral irradiance from the last solar minimum. Preliminary irradiances are in agreement with old measurements (work is still in progress on the instrument’s calibration). The irradiances show a clear increase with the solar cycle, more pronounced for lines formed at T > 1MK and after 1998. During maximum, the corona becomes hotter, and the characteristics of the `quiet Sun’ change.

30. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun Additional material

31. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun

32. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun

33. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun

34. UCL DEPT. OF SPACE & CLIMATE PHYSICS SOLAR & STELLAR PHYSICS GROUP EUV spectral irradiance of the Sun