Monitoring the solar UV irradiance spectrum from the observation of a few passbands

¹ LPC2E, UMR 6115, CNRS and University of Orléans, 3A avenue de la Recherche Scientifique, 45071 Orléans Cedex 2, France
e-mail: gael.cessateur@cnrs-orleans.fr
² LPG, UMR 5109, CNRS and University of Joseph Fourier, Bâtiment D de Physique, BP 53, 38041 Saint-Martin d’Hères Cedex 9, France
³ LATMOS, UMR 8190, CNRS, 11 boulevard D’Alembert, 78280 Guyancourt, France
⁴ Observatoire Royal de Belgique, Avenue Circulaire 3, 1800 Brussels, Belgium
⁵ Laboratory for Atmospheric and Space Physics, University of Colorado, 1234 Innovation Dr., Boulder, CO 80303, USA

Received: 10 October 2010
Accepted: 10 January 2011

Abstract

Context. The solar irradiance in the UV is a key ingredient in space weather applications; however, because of the lack of continuous and long-term observations, various indices are still used today as surrogates for the solar spectral irradiance.

Aims. As an alternative to current spectrometers we use a few radiometers with properly chosen passbands and reconstruct the solar spectral irradiance from their outputs. The feasibility of such a reconstruction is justified by the high redundancy in the spectral variability.

Methods. Using a multivariate statistical approach, we first compared six years of daily-averaged UV spectra and a selection of passbands (from existing radiometers) and solar indices. This leads to a strategy for defining those passbands that are most appropriate for reconstructing the spectrum.

Results. With four passdbands chosen from already existing instruments, we reconstruct the UV spectrum with a relative error of about 20%. Better performance is achieved with a combination of passbands than with a combination of indices.