the euv spectral irradiance of the sun from 1997 to date giulio del zanna pparc/stfc adv. fellow...
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The EUV spectral irradiance of the Sunfrom 1997 to date
Giulio Del ZannaPPARC/STFC Adv. Fellow
DAMTP, CMS, University of Cambridge
Vincenzo AndrettaOAC INAF, Italy
Tom Woods, Phil Chamberlin et al., LASP, Univ. of Colorado, USA
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
SOHO TRACE Yohkoh
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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.
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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.
B2/L
B1/L
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E XTRA SLIDES
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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
(Floyd 2005)
(Woods 2005)
UV EUV
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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
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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)
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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) .
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Pevtsov et a. (2003)
B2/L
B1/L
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