The lost sunspot cycle: Reanalysis of sunspot statistics

We have recently suggested that one low sunspot cycle was possibly lost in 1790s (Usoskin et al. 2001, A&A, 370, L31). In this paper we present the results of a rigorous statistical analysis of all available sunspot observations around the suggested additional cycle minimum in 1792 - 1793. First we estimate the uncertainty of a monthly mean sunspot number reconstructed from a single daily observation. Then we compare, using quantitative statistical tests, the average level of sunspot activity in 1792 - 1793 with the average activity during the minimum, mid-declining and maximum phases of cycles in the well-measured reference period 1850 - 1996. We show that, contrary to the results by Krivova et al. ( 2002), the level of sunspot activity in 1792 - 1793 is statistically similar to that in the minimum phase, and significantly different from that in the mid-declining and maximum phases. Using the estimated uncertainties, we also calculate new, weighted annual values of R(g) in 1790 - 1796 which show a clear minimum in 1792 - 1793 and a maximum in 1794 - 1795, supporting the idea of an additional weak cycle in 1790's.