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tokens: data using the observations from its Solar Optical Observing Network (SOON). Although in the past, the (SOON) data set was often used as a continuation of the RGO data set of sunspot areas, it has a known deficiency in the measurements of smallest sunspots and pores (e.g., Muñoz-Jaramillo et al. 2015 ). On the other hand, the observations of sunspot areas from the KMAS, which start in 1954, are more uniform and include the smallest sunspots and pores comparable to the RGO sunspot size limit. By their cumulative distribution, KMAS group areas are similar to RGO data (Muñoz-Jaramillo et al. 2015 , who established a proportionality constant between RGO sunspot group areas and KMAS as 1.07 or 0.93 to convert from KMAS to RGO). Thus, for the period 1977–2014, we employ sunspot areas observed at KMAS (Tlatov et al. 2016 ). 3. TWO POPULATIONS OF SUNSPOT GROUPS 3.1. Group Areas Sunspot groups are not static objects: as an active region develops its area increases and reaches a maximum within 2–3 days after its emergence (e.g., Pevtsov et al. 2003 ). According to a review article by van Driel-Gesztelyi Green ( 2015 ), a lifetime of active regions with fully developed sunspots varies between weeks and months. The rise phase takes between 3% and 15% of a group’s lifetime, which also translates to a few days from the beginning of the emergence of a group to the maximum of its development (maximum area). To take into account these evolutionary changes in group areas, for each group in the RGO–KMAS data set, we selected the largest area of this group. Since some groups will reach their maximum area on the side of the Sun not visible from Earth, one could expect a slight enhancement in small group areas. However, with a rapid growth phase of only a few days, we do not expect that such enhancement will have a significant effect on our conclusions. Figure 1 (a) shows the distribution of (logarithm of group areas) for the combined RGO–KMAS data set. The distributions were constructed using an equal bin size of Δ = 0.25 in the logarithm of group areas. The distribution is clearly bimodal, with one component peaking at about 16 M.S.H. (millionth of solar hemisphere, ) and the other at about 316 M.S.H. (). The former corresponds to a round feature with 7.6 Mm in diameter (a pore or a rudimentary sunspot) and the latter is about 350 Mm in diameter, or about the size of a regular sunspot. To separate the two components, we fit the observed distributions by a combination of two Gaussian functions. The fitting was done with the help of the data analysis software package “ORIGIN,” which uses the Levenberg–Marquardt algorithm to iteratively adjust the amplitude, mean, and standard deviation of each fitted Gaussian, until the best-fitted solution is found (e.g., Press et al. 1992 ). The fitted Gaussians are shown in Figure 1 (a) as blue profiles, and their sum is shown as a red double-peaked profile. Figure 1. (a) Distribution of group areas (log S ) from RGO data.