3 Discussions and conclusions

In this paper, we use the data of the X-ray flare ($M\geq 1$) events during the interval of 1987 to 1992 corresponding to the maximum period of the 22nd solar cycle in order to investigate the behavior of N-S and W-E asymmetries. In the present study we have found that the N-S asymmetry really existed for the flare events with the dominance of the southern hemisphere. The solar cycle 22 seems to have the same behaviour than the cycle 21 in respect to the N-S asymmetry. This study is complementary to the work of Garcia (1990) concerning his analysis using X-ray flares for Solar Cycles 20 and 21 and is in good agreement with studies of Solar Cycle 22 using different indicators (Verma 1992; Oliver & Ballester 1994; Joshi 1995).

The distribution of the X-ray $M\geq 1$ flares from 1987 to 1992 with respect to heliographic longitude shows that the flares were not uniformly distributed in longitude but we did not find any significant W-E asymmetry during the period, which confirms the results of Joshi (1995) for the same period of time.

The study of N-S asymmetry has to be continued in order to find some relationship between the existence of torsional oscillations observed by MDI on SOHO and the convection rolls suspected by Ribes et al. (1993) to explain the meridional circulation. All these studies would allow us to have a better insight into the solar dynamo system.

On the other hand, a long term study of N-S asymmetry has to be implemented to prove the existence of a long duration solar cycle superimposed to the 11 Solar Cycle which could correspond to the existence of a global magnetic field of long period variability (Verma 1987).

Acknowledgements

The author (LkJ) gratefully acknowledges the useful help in the input of the data used in this paper into a VAX computer from Zhang Xiaoyu of Yunnan Observatory and the help from P. Micheneau during his stay in DASOP, Meudon Observatory.

The author (LkJ) would like to express his gratitude for support and kind hospitality at the Observatoire during his scholar visit. The author (LKJ) is also indebted to Mr. Zhong Shuhua for his help and support.

We thank particularly Drs. Kleczek and Ballester who showed their interest in this study and favoured fruitful discussions which are partially reproduced in this paper, Dr G.Chambe who checked the probability computations and the unknown referee who helped us to clarify the manuscript.