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
(Del Zanna et al. 2005,2006, 2009)

2. G. Del Zanna - UKSP/NAM/JENAM 2009
Key questions
What is the EUV spectral irradiance and how it varies?
Can we model it ?
Does it affect our climate?
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 -- 1 MK
X-ray MK
"Winter Scene with Frozen Canal" by Aert van der Neer
SOHO
TRACE
Yohkoh
G. Del Zanna - UKSP/NAM/JENAM 2009

3. CALIBRATION CALIBRATION CALIBRATION
Why study UV and EUV ?
UV radiation could be a significant driver for terrestrial climate (e.g. Haigh 1996).
The EUV radiation creates the ionosphere and might also have an indirect effect.
Spectral irradiance measurements:
plenty in UV, almost none in X-rays and EUV (until TIMED 2002)
EUV irradiances
NASA TIMED/SEE
UV irradiances
CALIBRATION CALIBRATION CALIBRATION
Source: LASP, Univ. of Colorado)
G. Del Zanna - UKSP/NAM/JENAM 2009
Woods & Eparvier (2006)

4. G. Del Zanna - UKSP/NAM/JENAM 2009
CDS NIS
G. Del Zanna - UKSP/NAM/JENAM 2009

5. SOHO CDS NIS: 1000 exposures sampling the whole Sun in 13 hours
He I, O V (0.25), Mg X (1 MK), Fe XVI (2.5 MK)
`Del Zanna minimum’ ?
G. Del Zanna - UKSP/NAM/JENAM 2009

6. SDO EVE prototype
‘It could take a lifetime to understand such a spectrum’ (P.J.Storey, UCL)
Woods et al. (GRL, 2009) Chamberlin et al. (GRL, 2009)
G. Del Zanna - UKSP/NAM/JENAM 2009

7. SOHO NIS irradiances vs. EVE prototype
SDO/EVE
G. Del Zanna - UKSP/NAM/JENAM 2009

8. G. Del Zanna - UKSP/NAM/JENAM 2009
CDS NIS irradiances
G. Del Zanna - UKSP/NAM/JENAM 2009

9. Summary and further work SDO EVE vs. NIS radiances
The irradiances in lines formed in the low transition region have changed little (max 50%) over the last 12 years (also from late 60’s).
At 1 MK by a factor of 5 and at 2.5 MK by a factor of 40.
Further work:
Explain the Sun-as-a-Star and other stars in XUV with radiance measurements.
Improve predictions of EUV radiances and irradiances (current models use proxies: does not work!):
- climate models
- back in time.
thank you
B2/
G. Del Zanna - UKSP/NAM/JENAM 2009