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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
Key questions
1.
2.
3.
What are the characteristics of the EUV spectral irradiance and
its variations ?
Can we model the X-UV irradiance of the Sun and stars?
How does the solar atmosphere affect our climate?
Magnetogram
SOHOG. Del Zanna
EUV -- 1 MK
- NAM 2009
TRACE
X-ray -- 3-5 MK
Yohkoh
T vs. total irradiance
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.
"Winter Scene with Frozen Canal" by Aert van der Neer
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
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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)
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CDS NIS
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SDO EVE prototype
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CDS NIS 1 irradiances
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CDS NIS 2 irradiances
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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.
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XTRA SLIDES
SDO EVE
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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)
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Changes in Ionosphere during solar cycle
Ion density
X-ray
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The Solar spectrum
UV
EUV
(Woods 2005)
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Zanna
- NAM 2009
(Floyd
2005)
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
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)
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)
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
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B
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