Tuesday, February 2, 2010
An Assessment of Atlantic Multidecadal Variability based on Sea Surface Temperature Observations
The planetary-scale mode of variability of sea surface temperature widely known as the Atlantic multidecadal oscillation (AMO) plays an important role in climate variability on the decade to century time scale. We show that an AMO-like mode can be recovered as the second empirical orthogonal function (EOF2) of the global, monthly mean sea surface temperature (SST) field from which the global mean temperature has been removed. This mode is remarkable in terms of the long decorrelation time of its expansion coefficient time series and its striking resemblance to the pattern of 20th century SST trends. Its multidecadal temporal variability resembles that attributed to the AMO but it is not quasi-periodic. It exhibits a pronounced trend, reflecting the much slower rate of warming of the subpolar North Atlantic compared to the remainder of the world ocean. Implications for the interpretation of 20th century climate variability are discussed.