Hemispheric sunspot numbers 1874–2020

Context. Previous studies show significant north–south asymmetries for various features and indicators of solar activity. These findings suggest some decoupling between the two hemispheres over cycle evolution, which is in agreement with dynamo theories. For most important activity index, sunspot numbers, so far only limited data are available independently. Aims. The aim this study to create a continuous series daily monthly hemispheric numbers (HSNs) from 1874 2020, will be continuously expanded future HSNs provided by SILSO. Methods. Based on measurements areas 2016 Greenwich Royal Observatory National Oceanic Atmospheric Administration, we derive relative fractions northern southern applied international number (ISN) HSNs. This method obtained validated against published period 1945–2004 those SILSO 1992 2016. Results. We provide catalogue daily, mean, 13-month smoothed mean time range 1874–2020 –fully covering cycles 12 24– that consistent newly calibrated ISN (Clette et al., 2014). Validation reconstructed direct since 1945 reveals high level consistency, Pearson correlation coefficients r = 0.94 (0.97) (monthly mean) data. cumulative 12–24 give value 16%, no obvious pattern predominance evolution. strongest asymmetry occurs no. 19, hemisphere shows cumulated 42%. phase shift peaks may up 28 months, absolute 16.8 months. shifts reveal an overall reaching its maximum earlier (in 10 out 13 cases), signed −7.6 Relating HSN peak growth rates during rise amplitude higher correlations when considering individually, ≈ 0.9. Conclusions. Our further evidence degree evolves independently hemispheres, demonstrate empirical prediction methods can improved investigating dynamics terms