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A
North Pole
Moon
Sun's equator
seasonal path
Earth's equator
23.5˚
angle
Moon's angle to
Earth's equator
is 28.5˚
5˚ angle
South Pole
B
North Pole
9.3 years later
Sun's equator
Earth's equator
23.5˚
angle
Moon's
angle to
Earth's
equator
is 18.5˚
5˚ angle
South Pole
Schematic presentations of the 18.6-year lunar orbit relative to the Earth for A) lunar maxima and B) lunar minima.
Fig. 2.17
southern Africa and eastern Australia. A sampling of
these associations worldwide is presented for the
western United States and Canada, northern China,
India, the Nile region of Africa, and the mid-latitudes
of South America (Table 2.2). In all cases, except for
India, the mean discrepancy between the occurrence
of the hazard and peaks in the lunar tide is less than
one year. Not only is the 18.6-year cycle dominant, but
the data also show temporal and spatial bistable
phasing . In this process, drought may coincide with
maxima in the 18.6-year lunar cycle for one period, but
then suddenly switch to a minimum. This 'flip-flop'
happens every 100-300 years, with the most recent
occurring at the turn of the twentieth century in South
America, China, Africa, and India. On the Great
Plains, no bistable 'flip-flop' has occurred since 1657;
however, the last lunar cycle maximum in 1991 wit-
nessed flooding instead of drought in this region. At
present, disparate regions of the globe's major wheat
growing areas undergo synchronous periods of drought
that have major implications for the price of grain and
the relief of famine-stricken regions.
 
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