Regularity of the north-south asymmetry of solar activity K. J. Li, J. X. Wang, S. Y. Xiong, H. F. Liang, H. S. Yun and X. M. Gu A&A, 383 2 (2002) 648-652 Published online: 15 February 2002 DOI: 10.1051/0004-6361:20011799