On bistable phasing of 18‐6‐year induced drought and flood in the Nile records since AD 650

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Abstract
A maximum entropy analysis of winter and summer flood records of the Nile from ad 622 to 1490 shows evidence for periodic lunar nodal 18′6‐year(as well as weaker 10–11 year cyclic) induced drought/flood in regions of Africa drained by this river. This supports the results of Hameed (1984) who analyzed the same records using the Fourier transform method, and of Hameed and Currie (1985) who studied the summer flood records of the modern period (ad 1690–1962) using the maximum entropy method. The nodal term exhibits bistable phasing with respect to dates or epochs of maximum in the nodal tide, a phenomenon previously found in drought/flood proxy data in South America (Currie, 1983), in India (Currie, 1984a), in North America (Currie, 1984c), in China (Currie and Fairbndge, 1985), and in precipitation data for the northeastern United States (Currie, 1987c). Evidence for the 10–11 year solar cycle term in the Nile records is also discussed. Tyson (1980,1981) found terms near 19‐ and 11‐years in South African rainfall data, with the former exhibiting a bistable switch in phase at the beginning of our century, which is in agreement with results of Hameed and Currie (1985) for the modern Nile record.

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