Persistent active longitudes in the surface magnetic activity on the Sun

A novel analysis of sunspot data for the past 120 years reveals that sunspots in both northern and southern hemispheres are formed preferably in two persistent active longitudes separated by 180°. In the Carrington reference frame, the active longitudes continuously migrate in phase with respect to the Carrington meridian. The migration of the active longitudes is determined by changes of the mean latitude of sunspots and the surface differential rotation. The two active longitudes periodically alternate being the dominant region, similar to the 'flip-flop' phenomenon known in starspot activity. The period of the oscillations is about 3.8 and 3.65 years in the northern and southern hemispheres, respectively. The difference between the periods is significant and can be related to the known north-south asymmetry in the solar magnetic activity. Similar results are obtained from the analysis of large-scale surface magnetic fields using solar magnetic synoptic maps, for the cycles 20 to 23. The persistent active longitudes 180° apart, which migrate with the surface differential rotation and alternate their activity level with the 3.7-yr cycle, are found separately in positive and negative polarity fields. Our results provide new observational constraints for current solar dynamo models and strengthen the solar paradigm for magnetic activity on cool stars.