N-S Asymmetry and Periodicity of Solar Activity from Solar Cycles 21 – 24

Abstract

Continuous wavelet power spectrum approach has been utilized to examine the short- and long-term fluctuations of solar plage area (PA), solar flare index (SFI), and sunspot numbers (SSNs) from 1976 to 2022. Based on the distribution of monthly data from the hemisphere SSNs, the monthly average of the solar parameters under consideration has been divided into northern and southern groups. Besides, the N-S asymmetry, the periodicity, the interconnection, and phase synchronization between the northern and southern groups of the solar flare index and plage area have been presented using the wavelet technique. The findings show that the northern group of PAs has short and intermediate periods of 0.9, 1.5, 2.5, and 3.5 years, whereas the southern group shows the prevalence of periods of 0.7, 1.9, and 3.2 years. In contrast, the northern group of SFI displays periods of 0.6, 0.8, 1.5, and 3.5 years, whereas the southern group confirms the presence of discrete periods of 0.7 and 1.9 years. The PA and SFI data sets for the Solar Cycles (SCs) 21 – 24 show little correlation and fewer short periods in the cross-wavelet power spectra (XWT) and wavelet coherence (WTC) spectra between the northern and southern hemispheres.