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)

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

2

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

3


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 …

4


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)

5


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

6


We need EUV measurements that are

Spectrally resolved

Calibrated

Continuous

(S. Solomon, NCAR)

7


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))

8


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

9


10


Our hyposthesesOur hypostheses

Two lines with same dynamics

Same underlying physics (?)

No need to measure both lines

simultaneously

11


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,

12


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.

13


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

14


The « best » set depends on the application.

An example : the ionosphere

Lilensten et al., accepted in Ann. Geoph., 2007

15


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.

16


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?

17


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)

18


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. «

Documents

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)