A STUDY OF PHASE RELATIOSHIP AND NORTH-SOUTH ASYMMETRY OF SUNSPOT ACTIVITIES DURING CYCLES 21 -24

Abstract:

Sunspots represent the Sun’s magnetic activity which flips ~11 years. It is known that different solar activity indices are not symmetric between northern and southern hemispheres of the Sun and a phase lag exists which varies from cycle to cycle. The north-south asymmetry of the sunspot activity provides an important clue to understanding the solar dynamo action, especially with regard to the modern non-linear dynamo models. In this paper, we make a systematic analysis to investigate the phase lag between northern and southern hemispheric sunspot activity. The dominant hemisphere in each cycle from 21 to first 6 years of the current cycle 24 has been identified by calculating the statistical probability of hemispheric distribution of sunspot areas. The trend analysis have shown a southern hemisphere dominancy during cycles 21 and 23; whereas northern hemisphere dominates during cycles 22 and in the ascending phase of cycle 24.A detailed cross-correlative analysis has shown that during cycles 21 and 22 southern hemisphere was leading , but the reverse happened during solar cycles 23 and 24. We also investigate the periodic behavior of north-south asymmetry data of sunspot activity for solar cycles 21 -24. Power spectrum analysis exhibits a number of mid and long-term quasi-periodicities including well known Rieger type, annual and quasi biennial(QBO) periods and most of them are found to be time variable. Further, we have made a detailed study about the asymmetric nature and periodicities during prolonged minima of cycles 23/24. We discuss the possible explanations with the help of previous results, zonal flows, magnetic flux emergence and r-mode oscillations occurred inside the Sun.