Forecasts : McNish & Lincoln method

Forecasts of the monthly mean sunspot number using the McNish and Lincoln method. The base principle was described in McNish A.G. & Lincoln J.V. 1949, (Trans. Am. Geophys. Union 30, 673-685). The method was further refined in the mid-1970's by J.V. Lincoln (no published documentation), to include the latest solar cycles and to use monthly means instead of yearly means. These were the standard solar cycle predictions provided until recently by the SWPC-NOAA. Based on the original Fortran code kindly provided by the NCEI (NOAA, Boulder, USA), we reprogrammed the calculation in a modern form, while documenting this implementation. This method consists in least-square fitting a single mean cycle profile to the last 13-month smoothed sunspot number. This mean cycle is obtained by a simple averaging of all cycles between 1849 and 1975 (cycles 9 to 20), aligned on the time of their preceding minimum. This method can provide a reasonable prediction in the course of a cycle and a fair estimate of the upcoming maximum in the rising phase of the cycle. On the other hand, it is unusable around the times of cycle minima (+/- 1.5 year) and cannot provide any prediction of the expected length of a cycle (cf. Hildner, E. and Greer M.S, 1990, in R. I. Thompson, D. Cole, P. J. Wilkinson, M. A. Shea, and G. Heckman (eds.), Proceedings of Solar-Terrestrial Prediction Workshop III , NOAA and AFGL, USA. )