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Ann. Geophys., 23, 3055-3069, 2005
www.ann-geophys.net/23/3055/2005/
© European Geosciences Union 2005
Retrieving the solar EUV spectrum from a reduced set of spectral lines
T. Dudok de Wit1, J. Lilensten2, J. Aboudarham3, P.-O. Amblard4, and M. Kretzschmar5
1LPCE, CNRS and University of Orléans, 3A avenue de la Recherche Scientifique, 45 071 Orléans cedex 2, France
2LPG, CNRS and Joseph Fourier University, Bâtiment D de Physique, BP 53, 38 041 Saint-Martin d’Hères cedex 9, France
3LESIA, Paris Observatory, 5 Place Jules Janssen, 92 195 Meudon, France
4LIS, CNRS, 961 Rue de la Houille Blanche, BP 46, 38 402 St. Martin d’Hères cedex, France
5IFSI, INAF, Via del Fosso del Cavaliere, 00 133 Roma, Italy
Abstract. The solar EUV irradiance is a key input for thermospheric and ionospheric
models. Difficulties in continuously measuring the calibrated spectrum has
prompted the use of various surrogate quantities. Although most proxies
correlate quite well with the spectral variability, their use for modelling
purposes becomes increasingly unsatisfactory. A different and data-driven
approach is considered here, in which the EUV spectrum is reconstructed from
a linear combination of a few, calibrated and carefully selected spectral
lines. This approach is based on a statistical analysis of the temporal
variability of EUV spectra, as recorded by the TIMED satellite. A basic set
of lines is extracted, from which the salient features of the spectral
variability can be reconstructed. The best results are achieved with a
selection of 5 to 8 of these lines. This study focuses on the methodology for
selecting these lines, which can also be used for instrument specification
and provides new insight into the comparison of solar proxies against the EUV
irradiance.
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