Signature of the 27-day variation in hemispheric sunspot activity and asymmetry during 2010–2015

Abstract

In the present work, we study the time evolution, significance of the N-S asymmetry excesses presented as a function of the solar cycle and prominent rotational periods (∼27 d) separately for the northern and southern hemispheres. We have investigated short-term variations of the hemispheric solar activity (sunspot numbers and sunspot areas) during the time period 2010–2015, which covers the ascending and the maximum phase of solar cycle 24. We have implemented the Lomb-Scargle periodogram and continuous wavelet transform power spectrum techniques to study the time evolution and dominant rotational periods separately for the northern and southern hemispheres, and whole solar disk. Our results showed that the northern hemisphere exhibited longer solar synodic periods than the southern hemisphere, indicating that the northern hemisphere has a lower rotation rate. Moreover, the northern hemisphere was found to be dominant before transferring to the southern hemisphere during mid-2013. Also, the sunspot areas clearly demonstrated a two-peak structure of solar activity in the northern and southern hemispheres respectively during 2012 and 2014. The statistical significance of the southern hemisphere affirmed enhanced excess during the maximum phase of solar cycle 24.