Hemispheric Sunspot Numbers, in addition to the historical Sunspot Numbers that describe the activity of the whole Sun, provide important information on solar activity. Distinct asymmetries between the northern and the southern hemisphere appear concerning various aspects of solar activity: the location and height of the cycle maximum and the Gnevyshev gap, the alternating predominance of one hemisphere over the other, and the different rotational behavior of activity tracers in both hemispheres. These findings suggest that the magnetic field systems originating in the two hemispheres and their evolution in the course of the solar cycle are only weakly coupled. Finally, we stress that the various phenomena of N-S asymmetry in solar activity provide valuable constraints for solar dynamo theories.
Acknowledgements
The authors thank the former and present staff of the KSO for performing and making available the sunspot drawings, and also for helpful comments. We are grateful for the thoughtful comments of the referee, H. Balthasar. M.T., A.V. and A.H. gratefully acknowledge the Austrian Fonds zur Förderung der wissenschaftlichen Forschung (FWF grants P13653-PHY and P15344-PHY) for supporting this project.
Copyright ESO 2002