Observations and modelling of North-South asymmetries using a Flux Transport Dynamo

Abstract

The peculiar behaviour of the solar cycle 23 and its prolonged minima has been one of the most studied problems over the last few years. In the present paper, we study the asymmetries in active region magnetic flux in the northern and southern hemispheres during complete solar cycle 23 and rising phase of solar cycle 24. During the declining phase of solar cycle 23, we find that the magnetic flux in the southern hemisphere is about 10 times stronger than that in the northern hemisphere during the declining phase of the solar cycle 23 and during the rising phase of cycle 24, however, this trend reversed. The magnetic flux becomes about a factor of 4 stronger in the northern hemisphere to that of southern hemisphere. Additionally, we find that there was significant delay (about 5 months) in change of the polarity in the southern hemisphere in comparison with the northern hemisphere. These results provide us with hints of how the toroidal fluxes have contributed to the solar dynamo during the prolonged minima in the solar cycle 23 and in the rising phase of the solar cycle 24. Using a solar flux-transport dynamo model, we demonstrate that persistently stronger sunspot cycles in one hemisphere could be caused by the effect of greater inflows into active region belts in that hemisphere. Observations indicate that greater inflows are associated with stronger activity. Some other change or difference in meridional circulation between hemispheres could cause the weaker hemisphere to become the stronger one.