Influenced Over Decades

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Science  02 Feb 2001:
Vol. 291, Issue 5505, pp. 793
DOI: 10.1126/science.291.5505.793b

Sea surface temperatures (SSTs) in both the North Atlantic and the tropical Pacific exhibit significant multidecadal variability. It commonly has been assumed that variations in the two basins are independent of each other. Latif now suggests otherwise.

By analyzing and comparing time series of equatorial Pacific SST anomalies and the North Atlantic Oscillation (NAO) index, he shows that periods of unusually high Pacific SSTs are followed by development of an Atlantic-basin SST dipole after a lag of about 30 years. These changes, he believes, are linked by an “atmospheric bridge” that transfers less fresh water from the Pacific to the Atlantic when Pacific SSTs are higher. A lower fresh water flux perturbs Atlantic sea surface salinities, which in turn modifies the thermohaline circulation and thereby affects SSTs. Using an atmospheric general circulation model, Latif shows that such a mechanism can hindcast the fresh water fluxes that accompany Pacific SST changes and the NAO in a manner consistent with other models and observational evidence. Finally, he speculates that North Atlantic thermohaline circulation will strengthen during the coming decades in response to the recent rapid increase in tropical Pacific SSTs, thereby weakening the NAO and influencing the climates of North America and Europe. — HJS

Geophys. Res. Lett. 28, 539 (2001).

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