The severity of the east Asian summer monsoon, which affects more than 1 billion people, may be better forecast by analysing the North Atlantic Oscillation (NAO). This describes a large-scale system in which atmospheric pressure rises and falls in a see-saw motion from the polar to the subtropical region.
The monsoon's strength has been linked to the El Niño and La Niña cycles, but the NAO connection may further improve predictions, say Zhiwei Wu of the Chinese Academy of Sciences in Beijing and colleagues.
By combining data on global precipitation and atmospheric circulation with other indices of atmospheric activity, the researchers found that changes in the spring NAO can influence how strong or weak the monsoon gets later in the year.
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Atmospheric science: Monsoon madness. Nature 461, 850 (2009). https://doi.org/10.1038/461850b