ESWW4, Brussels, Novembre 2006 Retrieving the EUV solar spectrum from a selected set of lines for space weather purposes: A review of theories, models

ESWW4, Brussels, Novembre 2006

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)


Importance of EUV flux for space weather purposes

Influences the near space environment (ionosphere / thermosphere)

Wavelength


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


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


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+


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


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


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


3) To measure the full spectrum ?. Difficult and expensive

Schmidtke et al., Tiger program, Adv. Sp. Res., 10, 1553-1559, 2002


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.


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


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


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?


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


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


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,


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


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


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.


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

Documents

ESWW4, Brussels, Novembre 2006 Retrieving the EUV solar spectrum from a selected set of lines for space weather purposes: A review of theories, models