AbstractSpectrum analysis of 1197 USA air temperature records yields evidence for two peaks with periods 18.8 ± 1.7 and 10.4 ± 0.5 years. Tests by thet‐statistic show that both are significant at confidence levels of 99.9 per cent, and both account for 23 per cent of total variance in the raw data. They are identified as the luni‐solar 18.6‐year Mnand solar cycle Sc10–11‐year signals in climate, induced by the twelfth largest constituent tide acting on the Earth and a variation of 10 to 11 years in the Sun's luminosity of the order of 0.1 per cent. Amplitude and phase of Mnwavetrains are highly non‐stationary with respect to both time and geography; in particular, abrupt 180° phase changes in wave polarity are often observed. Amplitude and phase of the Scwaves are also highly non‐stationary, with those east of the Rocky Mountains out of phase with waves to the west. These results consolidate and greatly extend and clarify earlier studies of Currie based on far le