16-month periodicity of cosmic-ray intensity

Data from four neutron monitors, Climax (1953-1976), Deep River (1964-1977), Mt. Norikura (1957-1983) and Tokyo (1970-1983) are analysed. Power spectra reveal peaks at frequency 1c/16 months for all the stations. Harmonic analysis for the 16-month period is performed after eliminating the long-term solar-cycle variation. There is general agrrement in the phases of the mean vectors for various neutron monitors. The amplitude averaged over all the four stations is 0.41±0.01, while it is higher for the two stations having lower cut-off rigidity as compared to that of the other two