Analysis of the Hemispheric Sunspot Number Time Series for the Solar Cycles 18 to 24

In this article, we investigate temporal and periodic variations of the hemispheric sunspot number using sunspot data from Kanzelhohe Solar Observatory (KSO) for the time period of 1944 – 2017, which covers Solar Cycles 18 to 23 and almost the entire Solar Cycle 24 (2009 – 2017). The KSO data set was verified against the International Sunspot Number (ISSN) data. Temporal and periodic variations in the KSO data were analyzed using cross-correlation analysis, Morlet wavelet and multitaper (MTM) period analysis methods. We find that: i) sunspot numbers, as derived from both KSO and ISSN time series, are highly correlated with one another; ii) the temporal evolution of the sunspot number differs from one hemisphere to another with the solar cycle peaking at different times in each hemisphere; iii) the northern hemisphere showed two- and seven-month lead in Solar Cycles 18 and 19, respectively, while the southern hemisphere was leading in the rest of the cycles with the varying lead time ranging from 2 to 14 months; iv) apart from the fundamental mode of ≈ 11 years, Solar Cycle, the KSO data also show several midterm variations in the opposite hemispheres, specifically, Rieger-type and quasi-biennial periodicities – the detected midterm periodicities also differ in the northern and southern hemispheres; v) our results confirm the Waldmeier effect, which correlates the rise time with the cycle amplitude using the new sunspot data set from KSO.