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The EUV spectral irradiance of the Sun from minimum to maximum

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. Open questions. What are the characteristics of the EUV irradiance? What are its long-term variations?

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The EUV spectral irradiance of the Sun from minimum to maximum

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  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. 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 EUV spectral irradiance of the Sun

  3. Global warming Last 10 years probably the warmest in the last 8 000 years ! EUV spectral irradiance of the Sun

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

  5. Solar vs. anthropogenic and other (e.g. Volcanoes) effects (Lean 1997) EUV spectral irradiance of the Sun

  6. Fröhlich 2005, updated Fall 2004 AGU poster 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. EUV spectral irradiance of the Sun

  7. The Solar spectrum UV EUV (Floyd 2005) (Woods 2005) EUV spectral irradiance of the Sun

  8. 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) EUV spectral irradiance of the Sun

  9. EUV `Hole’ 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. (Floyd 1997) EUV spectral irradiance of the Sun

  10. TIMED: UV irradiance since 2002 Variability increases toward the EUV (Woods et al 2005) Grey areas show the variability during 2002-2004 EUV spectral irradiance of the Sun

  11. 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. EUV spectral irradiance of the Sun

  12. Variability in the EUV from SOHOSolar 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? EUV spectral irradiance of the Sun

  13. 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 EUV spectral irradiance of the Sun

  14. The EUV spectrum is dominated by emission lines OSO 3: Hall & Hinteregger (1970) EUV spectral irradiance of the Sun

  15. 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 EUV spectral irradiance of the Sun

  16. SOHO/EIT vs. Magnetograms (SOHO/MDI) EUV spectral irradiance of the Sun

  17. 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 EUV spectral irradiance of the Sun

  18. Histograms of the EIT intensity distributions EUV spectral irradiance of the Sun

  19. EUV spectral irradiance of the Sun

  20. EUV Irradiances from GIS EUV spectral irradiance of the Sun

  21. EUV Irradiances from GIS EUV spectral irradiance of the Sun

  22. EUV irradiances compared to previous records EUV spectral irradiance of the Sun

  23. 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 EUV spectral irradiance of the Sun

  24. Transition region – O III, O V EUV spectral irradiance of the Sun

  25. Mg X – 1MK EUV spectral irradiance of the Sun

  26. Corona at 2-3 MKSi XII – Fe XVI EUV spectral irradiance of the Sun

  27. EUV Irradiances from NIS EUV spectral irradiance of the Sun

  28. EUV Irradiances from NIS compared to previous records EUV spectral irradiance of the Sun

  29. 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. EUV spectral irradiance of the Sun

  30. Additional material EUV spectral irradiance of the Sun

  31. EUV spectral irradiance of the Sun

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  34. EUV spectral irradiance of the Sun

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