Luni‐solar 18.6‐ and 10–11‐year solar cycle signals in South African rainfall

Spectrum analysis of 59 South African rain‐gauge records yields evidence for two peaks with periods 18.2·1.4 years (57 out of 59 series covering virtually the entire country) and 10.3·0.5 years (in 37 series covering almost all except easternmost South Africa). They are identified as the luni‐solar 18.6‐year M n and 10–11‐year solar cycle S c signals in climate; their phases and amplitudes are non‐stationary with respect to both time and geography and, in particular, 180° phase changes in wave polarity are observed. These phase changes occurred in the early part of the century and by mid‐epochs 1964.0 and 1982.6 (mid‐epochs are dates of minimum in M n tidal forcing) a unipolar cell of drought encompassed virtually the entire nation. Constructive interference by the S c wave, which reached a minimum near 1981, exacerbated the droughts of mid‐epoch 1982.6 which were more severe than even those of the 1960s. The results confirm and extend in many respects those found by P. D. Tyson and his co‐workers in the 1970s.