EDP Sciences
Free access
Issue A&A
Volume 452, Number 2, June III 2006
Page(s) 631 - 639
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20064809



A&A 452, 631-639 (2006)
DOI: 10.1051/0004-6361:20064809

Reconstruction of solar UV irradiance in cycle 23

N. A. Krivova1, S. K. Solanki1 and L. Floyd2

1  Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
    e-mail: natalie@mps.mpg.de
2  Interferometrics Inc., 13454 Sunrise Valley Drive, Herndon, VA 20171, USA
    e-mail: linton.floyd@nrl.navy.mil

(Received 4 January 2006 / Accepted 26 February 2006)

Abstract
Solar irradiance variations show a strong wavelength dependence. Whereas the total solar irradiance varies by about 0.1% during the course of the solar cycle, variations at the wavelengths around the Ly-$\alpha$ emission line near 121.6 nm range up to 50-100%. These variations may have a significant impact on the Earth's climate system. Being almost completely absorbed in the upper atmosphere, solar UV radiation below 300 nm affects stratospheric chemistry and controls production and destruction of ozone. Models of the solar UV irradiance remain far from perfect, even though considerable progress has been made in modelling the irradiance variations longwards of about 200-300 nm. We show that after correcting for the exposure dependent degradation of the SUSIM channels sampling irradiance at $\lambda >240$ nm (making use of the Mg II core-to-wing ratio) the agreement between model and measurement is significantly improved. At shorter wavelengths the LTE approximation usually made in such models fails, which makes a reconstruction of the solar UV irradiance a rather intricate problem. We choose an alternative approach and use the observed SUSIM UV spectra to extrapolate available models to shorter wavelengths. The model reproduces observed solar cycle variations of the irradiance at wavelengths down to 115 nm and indicates an important role of UV irradiance variability: up to 60% of the total irradiance variations over the solar cycle might be produced at wavelengths below 400 nm.


Key words: Sun: activity -- Sun: faculae, plages -- Sun: magnetic fields -- solar-terrestrial relations -- sunspots -- Sun: UV radiation




© ESO 2006

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.

Editor-in-Chief: T. Forveille
Letters Editor-in-Chief: J. Alves
Managing Editor: C. Bertout

ISSN: 0004-6361 ; e-ISSN: 1432-0746
Frequency: 12 volumes per year
Published by: EDP Sciences

Mirror sites: CDS | EDP Sciences
  RSS feeds
© The European Southern Observatory (ESO)