EDP Sciences
Free access
Volume 401, Number 3, April III 2003
Page(s) 1151 - 1157
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20030216

A&A 401, 1151-1157 (2003)
DOI: 10.1051/0004-6361:20030216

The apparent longitude distribution of solar flares

A. J. Conway1 and S. A. Matthews2

1  Dept. of Physics & Astronomy, The Open University, Milton Keynes MK7 6AA, UK
2  Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK

(Received 8 August 2002 / Accepted 14 February 2003 )

The distribution of solar flares in solar disk longitude averaged over many solar rotations must be uniform. However, heliographic longitude distributions constructed from observed flare locations are obviously not uniform. In the wavelength ranges we consider (hard and soft X-rays and H $\alpha$), where the emission is presumed to be nearly isotropic, we find a wavelength-dependent bias such that fewer flares than expected occur near the limb. We can explain this bias in terms of the method of locating the flare (from H $\alpha$) and the flare magnitude and duration. This work has implications that are relevant to measuring directivity in emission processes and also the possibility of identifying limb flares by statistical means in catalogues rather than by the time-consuming inspection of images.

Key words: Sun: magnetic fields -- Sun: flares -- methods: statistical -- Sun: activity

Offprint request: A. J. Conway, a.j.conway@open.ac.uk

© ESO 2003