Variance contribution of luni‐solar and solar cycle signals in the St Lawrence and Nile river records

Spectrum analysis of the St Lawrence River and three Nile River hydrological records yields evidence for two peaks with periods near 19 and 11 years. For each series the wavetrains of the peaks are obtained by bandpass filters, summed, superimposed on trend‐like components in the raw data, and plotted against the raw data. The contribution of the two waves to total variance in the St Lawrence data is 42 per cent, whereas the mean contribution in the Nile records varies from 20 to 28 per cent. The waves are identified as the 18–6‐year luni‐solar Mn 10–11‐year solar cycle Sc signals in climate, which have also recently been reported in other variables such as precipitation (USA, UK, South Africa, India), tree‐ring chronologies (world‐wide), air temperature and air pressure (world‐wide), height of sea‐level (world‐wide), and sea‐surface temperature, as well as in economic variables such as American crop yield, European fish catches, dates of wine harvest, and other macro‐economic data (Currie, 1988; Currie et al., 1993). The polarity of the 19‐year St Lawrence wave changed phase 180° between epochs 1936–1 and 1954–7 (epochs are dates of maximum in tidal forcing), and this phenomenon is commonly found in the much longer Nile records, as well as in virtually all of the above mentioned climate parameters.