Variability of the annual amounts of station precipitation revealed by autocorrelation functions and power spectra

The rainfall in Seoul, comprising "Chugugi" and modern rain-gauge measurements, shows a resilient autocorrelation peak at a time lag of 11 years and a statistically reliable suppression of the 11-year frequency in the associated spectrum function. We confirmed a similar signature in the averages of the autocorrelations and spectra of the Global Historical Climatology Network precipitations. Approximately half of the selected 3,065 stations showed the autocorrelation peak, and the associated power suppression of the 11-year period or frequency. For the global average, the spectrum suppression was pronounced, and the associated correlation peak was less notable. We were able to simulate the suppression of power by modulating white noise time series representing precipitation with a sinusoidal time series of a given frequency. For modulation, we used multiplication instead of addition. The nonlinear process seems to be the principal mechanism in the influence of the 11-year solar cycle on precipitation.