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Retrieving the EUV solar spectrum from a selected set of lines for space weather
purposes: A review of theories, models and experiments
J. Lilensten, T. Dudok de Wit, M. Kretzschmar, P.-O. Amblard, S. Moussaoui, J. Aboudarham and F.
Auchère (ias)
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Importance of EUV flux for space weather purposes
Influences the near space environment (ionosphere / thermosphere)
Wavelength
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Result (amongst other phenomena) in •Dilatation of the thermosphere (density may increase by a factor of 10 at the altitude of the International Space Station)
•rapid variations, creations of small scale disturbances, winds
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Pap and Frölich, 1999; Nesme-Ribes and Thuiller, 2000
Variations are not linear
ESWW4, Brussels, Novembre 2006CELIAS/SEM experiment, Bochsler, 1999
14 July 1998
27 days
Their characteristic variation times range from the second to several years
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2) Existing models for Aeronomy. Poorly sampled and / or based on too short data sets (2 years with TIMED)
Torr and Torr (1985)
SC#21REF, f10.7 = 70
F79050, f10.7 = 243
He+ et Si9+
Fe14+
Si10+ et He+
Mg10+
Ne6+O5+
He
O3+et Mg9+
O4+
O++
N3+et Ne7+
O3+
C++
Lyman
O5+
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SERF / HFGTorr, M.R., and D.J. Torr, J. Geophys. Res. 90, 6675-6678, 1985
EUV / SOLAR 2000Tobiska, W. K. and F. Eparvier, Sol. Phys., 177, 147-159, 1998
EUVAC / HEUVACRichards, P. G., J. A. Fennelly, and D.J. Torr, J. Geophys. Res. 99, 8981-8992, 1994P. G. Richards, T. N. Woods, and W. K. Peterson, Adv. Spa. Res., 37, 315-322,2006
NRLEUVLean et al, J. Geophys. Res. 108, 1059, 2003Warren et al., J. Geophys. Res. 106, 15 745, 2001
Other:Nusinov A. A., models for prediction of EUV and W-ray solar radiation based on 10.7 cm radio emission, Ed. R.F. Donnely, NOAA ERL, 1992
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2) Existing models for Aeronomy. Based on indices (Ri, f10.7, Mg …) or proxies (E10.7, X10.7, Iu …)(see poster P2.7, Menvielle)
Year
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2) Existing models for Aeronomy. The proxies are NOT well correlated to the solar activitySee poster P3.14, Dudok de Wit et al.
T. Dudok de Witet al., Which solar EUV proxies are best for reconstructing the solar EUV irradiance?, submitted to Adv. Spac. Res., 2006
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3) To measure the full spectrum ?. Difficult and expensive
Schmidtke et al., Tiger program, Adv. Sp. Res., 10, 1553-1559, 2002
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Today : only Solar Extreme Ultraviolet Experiment (SEE) onboard TIMED (NASA)
XPS
EGS
EUV Grating Spectrograph (EGS) 25 à 200 nm 0.4 nm spectral resolution.
XUV Photometer System (XPS) 0.1 to 35 nm in 12 spectral bands
Woods, et al., Solar EUV Experiment (SEE): mission overview and first results. J. Geophys. Res., 110, 1312-1336, 2005.
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Retrieve the flux variation through their effects
- On electron density profiles (Mikhailov and Schlegel, Ann. Geoph., 18, 1164 – 1171, 2000)
- On the E region critical frequency (Nusinov, Adv. Space Res., 37, 426-432, 2006)
- On the thermospheric emission (Singh and Tyagi, Adv. Space Res., 30, 255è-2562, 2002)
- On wind or temperatures (Zhang et al., Geoph. Res. Lett., 29, 10.029/2001GL013579, 2002)
…
Several attempts to retrieve the full spectrum
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These method depend all on a given model:
- They cannot be general- They cannot be used as operationnal tools
- They are absolutely required for tests
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Reduce the solar spectrum to a limited (3) set of characteristic spectra: very promissing method through positive source separation
SEE (TIMED) : reconstruction < 2%
Quiet sun contribution?
Active zone contribution?
Hot lines contribution?
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Physics through Differential Emission Measure: 6 to 10 lines are necessarySee poster P6.4, Kretzschmar et al.
M. Kretzschmar et al., Retrieving the Whole Solar EUV Flux from 6 Irradiance Line Measurements, Advances in Space Research, 37, 341–346, 2006
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Use statistics (Singular Value Decomposition): 6 to 10 lines are necessary. Same conclusion through 2 totally different approaches
T. Dudok de Wit, et al., Retrieving the solar EUV spectrum from a reduced set of spectral lines, Annales Geophysicae, 23, 3055–3069, 2005
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How to choose the lines to be observed?
Dendrogram of 38 spectral lines using an average distancelinkage between all lines.
Statistical analysis of TIMED/SEE data. Using twoyears of daily EUV spectra and classification techniques,
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This table allows to select the best set of lines to observe in order to reconstruct the total flux with the best accuracy.
The relative global error for the best combination of 6 lines yields to 3.7% and less than 0.25% with 10 lines
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However, the « best » set may depend on the application. An example : the ionosphere
How to choose an observed set of solar lines for aeronomy driven applications, J. Lilensten et al., submitted to Ann. Geoph., 2006
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Using a multidimensional scaling technique :
H I at 102.572 nmCIII at 97.702 nmOV at 62.973 nmHeI at 58.433 nmFeXV at 28.415 nmHeII at 30.378 nm
Allows to retrieve the full solar spectrum with a relative global error of 6.8 % and still fulfill ionospheric physics requirements.
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Near future: LYRA, the Solar VUV radiometer on-board PROBA IIJ.-F. Hochedez et al., Adv. Space Res., 37, Iss 2, 303-312, 2006http://lyra.oma.be/index.php
1/ Lyman-alpha (115-125 nm)2/ the 200-220 nm range 3/ Al filter channels (17-70 nm4/ MgF2 windows (120-220 nm),
And EVE on-board SDOhttp://lasp.colorado.edu/eve/eve_home.html