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Issue A&A Volume 409, Number 2, October II 2003 Page(s) L17 - L20 Section Letters DOI 10.1051/0004-6361:20031292

A&A 409, L17-L20 (2003)
DOI: 10.1051/0004-6361:20031292

Letter

Statistical characterisation of full-disk EUV/XUV solar irradiance and correlation with solar activity

J. Greenhough¹, S. C. Chapman¹, R. O. Dendy^{2, 1}, V. M. Nakariakov¹ and G. Rowlands<sup>1

1</sup>  Department of Physics, University of Warwick, Coventry CV4 7AL, UK
    e-mail: {greenh,sandrac,valery}@astro.warwick.ac.uk; g.rowlands@warwick.ac.uk
²  UKAEA Culham Division, Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB, UK
    e-mail: richard.dendy@ukaea.org.uk

(Received 7 May 2003 / Accepted 22 August 2003)

Abstract
We investigate the distribution of fluctuations in solar irradiance when integrated over the full disk, obtained using extreme ultraviolet/soft X-ray observations from the SOHO CELIAS/SEM instrument. This time series sums over both the contributions of single distinguishable flares, and of many other processes. By detrending we select events with timescales of less than a few hours such as waves, slow flows, and CMEs. The statistics generated by this range of phenomena can be characterised by power-law-tailed distributions. We show that (i) during the high activity period 2000 Jan.-June the tail exponent ; (ii) during the low activity period 1996 Jan.-June ; and (iii) in general decreases with increasing activity.

Key words: Sun: activity -- Sun: corona -- Sun: flares -- Sun: UV radiation -- Sun: X-rays

Offprint request: J. Greenhough, greenh@astro.warwick.ac.uk

© ESO 2003

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