1. The EUV spectral irradiance of the Sun from 1997 to date Giulio Del Zanna PPARC/STFC Adv. Fellow DAMTP, CMS, University of Cambridge Vincenzo Andretta OAC INAF, Italy Tom Woods, Phil Chamberlin et al., LASP, Univ. of Colorado, USA

2. G. Del Zanna - NAM 2009 Key questions 1.What are the characteristics of the EUV spectral irradiance and its variations ? 2.Can we model the X-UV irradiance of the Sun and stars? 3.How does the solar atmosphere affect our climate? X-ray -- 3-5 MKEUV -- 1 MKMagnetogram SOHOTRACEYohkoh

3. G. Del Zanna - NAM 2009 T vs. total irradiance "Winter Scene with Frozen Canal" by Aert van der Neer 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.

4. G. Del Zanna - NAM 2009 Why study UV and EUV ? UV radiation controls the amount of stratospheric ozone and 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. Plenty of UV measurements, almost none in X-rays and EUV NASA TIMED/SEE EUV irradiances

5. G. Del Zanna - NAM 2009 The EUV spectral radiances of the whole Sun from SOHO/CDS SOHO/CDS 1000 single slit exposures sampling the whole Sun in 13 hours from 1998 Si XII (2 MK) SOHO/CDS (Del Zanna et al. 2005,2006) Mg X (1 MK)

6. G. Del Zanna - NAM 2009 CDS NIS

7. G. Del Zanna - NAM 2009 SDO EVE prototype

8. G. Del Zanna - NAM 2009 CDS NIS 1 irradiances

9. G. Del Zanna - NAM 2009 CDS NIS 2 irradiances

10. G. Del Zanna - NAM 2009 Summary and further work Used SOHO/CDS to describe the EUV spectral radiances and obtain irradiances. The ‘quiet Sun’ from chromosphere to 1 MK corona has been very constant over the last 12 years (and more). Further work:  Relate EUV radiances to their magnetic fields.  Improve predictions of EUV radiances (current models use proxies: does not work!) Climate models: predict the EUV irradiance back in time and for other stars. B2/LB2/L B1/L

11. G. Del Zanna - NAM 2009 EXTRA SLIDES

12. G. Del Zanna - NAM 2009 SDO EVE

13. G. Del Zanna - NAM 2009 The EUV and UV UV radiation controls the amount of stratospheric ozone and 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)

14. G. Del Zanna - NAM 2009 Changes in Ionosphere during solar cycle Ion density X-ray

15. G. Del Zanna - NAM 2009 The Solar spectrum (Floyd 2005) (Woods 2005) UV EUV

16. G. Del Zanna - NAM 2009 Does the quiet Sun have a cycle ? 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

17. G. Del Zanna - NAM 2009 Proxies Most cycle proxies vary in phase with the sunspot number. Scalings between proxies are generally non-linear. Proxies vary among stars (Spot-to-plage ratio likely depends on activity level)

18. G. Del Zanna - NAM 2009 The Sun as a star Model EUV irradiances in other stars. Model the solar X-ray irradiance to explain quiescent emission in young stars (cf. Del Zanna et al. 2006). Pevtsov et a. (2003) B2/LB2/L B1/L

19. G. Del Zanna - NAM 2009