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Retrieving the EUV solar spectrum from a selected set of lines for space
weather purposes
Retrieving the EUV solar spectrum from a selected set of lines for space
weather purposes
Jean Lilensten (LPG, Grenoble) Thierry Dudok de Wit (LPCE,
Orléans)Jean Aboudarham (LESIA, Meudon)Pierre-Olivier Amblard (LIS,
Grenoble)Frédéric Auchère (IAS, Orsay)
Matthieu Kretzschmar (ROB, Brussels)
+ COST 724 team
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COST 724:Developing the scientific basis for monitoring, modelling and predicting Space Weather
INPUTS
Specification of the ionosphereSpecification of the ionosphere
Ionosphere-thermospherespecification
models
Ionosphere-thermospherespecification
models
- electric fields
- atmospheric tides
- solar EUV flux
USERS
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COST 724:Developing the scientific basis for monitoring, modelling and predicting Space Weather
Can one use proxies instead ?
Dudok de Wit et al., 2007, accepted
We define the degree of similarity between 2 observables by means of their Euclidian distance. The observables may be time series or measureable parameters such as densities …
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COST 724:Developing the scientific basis for monitoring, modelling and predicting Space Weather
In order to define the axis, we use the Singular Value Decomposition. In our case, 2 to 3 modes are enough to describe over 95% of the variance.
Line orproxy 2Line or
proxy 1
Line orproxy 3
This degree is then represented on a dissimilarity map (called connnectivity map)
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COST 724:Developing the scientific basis for monitoring, modelling and predicting Space Weather
Sunspot
number
Sunspot
number
F10.7 indexF10.7 index
Mg II indexMg II index
wavelength [nm]
They are all aligned !!! The proxie cannot and will never suffice to retrieve the solar spectrum whatever the combination (linear or not)Dudok et al., 2006
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COST 724:Developing the scientific basis for monitoring, modelling and predicting Space Weather
We need EUV measurements that are
Spectrally resolved
Calibrated
Continuous
(S. Solomon, NCAR)
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COST 724:Developing the scientific basis for monitoring, modelling and predicting Space Weather
Instead of measuring the full EUV spectrum, why not measure just a few spectral lines with a dedicated instrument, and use these as inputs ?
6 to 10 lines should be enough, based on the inversion of the DEM Kretzschmar et al., ASR 37 (2006)Our approach : use four years of EUV spectra from TIMED and a statistical approach to determine which spectral
lines are the best for reconstructing the full spectrum (Dudok de Wit et al., Ann. Geoph (2005))
Our approach : use four years of EUV spectra from TIMED and a statistical approach to determine which spectral
lines are the best for reconstructing the full spectrum (Dudok de Wit et al., Ann. Geoph (2005))
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COST 724:Developing the scientific basis for monitoring, modelling and predicting Space Weather
TIMED : 4 years of daily spectra (2002-2006) from the EGS/SEE spectrometer (level 2 data)
spectral range : 26 - 195 nm
spectral resolution : 0.4 nm
flares are not (yet) included
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COST 724:Developing the scientific basis for monitoring, modelling and predicting Space Weather
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COST 724:Developing the scientific basis for monitoring, modelling and predicting Space Weather
Our hyposthesesOur hypostheses
Two lines with same dynamics
Same underlying physics (?)
No need to measure both lines
simultaneously
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COST 724:Developing the scientific basis for monitoring, modelling and predicting Space Weather
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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COST 724:Developing the scientific basis for monitoring, modelling and predicting Space Weather
The EUV spectrum can indeed be retrieved from a small set of spectral lines, and with good accuracy (< 1% ave error).
We have a rigorous statistical procedure for selecting those lines.
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COST 724:Developing the scientific basis for monitoring, modelling and predicting Space Weather
Which lines are the best ?Which lines are the best ?
The best choice is very much application dependentFor aeronomy ?Best fit of the EUV irradiance ?Best fit of the variability ?…
10 best combinations of 6 lines Dudok de Wit et al., AnnGeo 2005
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COST 724:Developing the scientific basis for monitoring, modelling and predicting Space Weather
The « best » set depends on the application.
An example : the ionosphere
Lilensten et al., accepted in Ann. Geoph., 2007
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COST 724:Developing the scientific basis for monitoring, modelling and predicting Space Weather
Using a multidimensional scaling technique :
H I at 102.572 nmCIII at 97.702 nmOV at 62.973 nmHeI at 58.433 nm
FeXV 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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COST 724:Developing the scientific basis for monitoring, modelling and predicting Space Weather
Next future: To 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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COST 724:Developing the scientific basis for monitoring, modelling and predicting Space Weather
Next future too:Use of a Neural Network (STSM T. Yapici and E. Altunas to France, scheduled in June and postponed after 1st September for budgetary reasons)
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COST 724:Developing the scientific basis for monitoring, modelling and predicting Space Weather
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« unprecedented spectral resolution, temporal cadence, and precision. «