Astron. Astrophys. Suppl. Ser. 131, 99-104

Statistical analysis of the X-ray flares $\sf ({\it M}\geq 1)$ during the maximum period of solar cycle 22

K.-J. Li^1,2 - B. Schmieder ^3,4 - Q.-Sh. Li²

Send offprint request: B. Schmieder

1 - CCAST (World Laboratory), P.O. Box 8730, Beijing, 100080, China
2 - Yunnan Observatory, Kunming, China
3 - Observatoire de Paris, Section de Meudon, URA 2080, 92195 Meudon Principal Cedex, France
4 - University of Oslo, Blindern, P.O. Box 1029, Norway

Received March 19, 1997; accepted February 11, 1998

Abstract:

The data of the X-ray flare events of class $M\geq 1$ during the interval of 1987 to 1992 corresponding to the maximum period of the 22nd solar cycle have been investigated to study the North-South (N-S) and West-East (W-E) asymmetries. During that period it has been shown the existence of a real N-S asymmetry. That confirms recent studies done by using other indicators, such as sunspot areas (Oliver & Ballester 1994). The E-W asymmetry during that period is not significant but a non uniform flare distribution in longitude has been evidenced. That result is also in good agreement with the work made by Joshi (1995) using H$\alpha$ flares for the same time period.

We have shown that the behaviour of the reverse tendency of Solar Cycle 21 to exhibit a predominance of the southern hemisphere in the N-S asymmetry compared to the previous Solar Cycles (19 and 20) is maintained for Solar Cycle 22. A long period cycle of the N-S asymmetry could be suspected.

Key words: Sun: activity -- Sun: flares -- Sun: X-rays