Characteristics of sunspot longitudinal distribution and their correlation with solar activity in pre-Greenwich data

We study and compare characteristics of the sunspot group latitude distribution in two catalogs: extended Greenwich (1874–2014) and Schwabe (1825–1867) (Arlt et al., 2013). We show that both datasets reveal similar correlations between the latitude and amplitude characteristics of the 11-year cycle: the latitude dispersion correlates with the current activity and the sunspot mean latitude at the cycle’s maximum is proportional to its amplitude. This agrees with the conclusions drawn in (Ivanov et al., 2011; Ivanov and Miletsky, 2014) for the Greenwich catalog. We show that the latitude properties of the sunspot distribution are much more tolerant to gaps in observational data than traditional amplitude indices of activity. Therefore, the discovered correlations can be used for estimation of the observation quality and independent normalization of the activity levels in spotty pre-Greenwich data. We exemplified this using the Schwabe catalog. In addition, we show that the first part of the Schwabe data probably contains errors in sunspot latitudes, which lead to overestimation of the sunspot latitude dispersions.