Revisiting the role of atmosphere-ocean coupling in North Atlantic variability and predictability

Thursday, 18 December 2014: 12:05 PM
Laure Zanna, University of Oxford, Dept of Physics, Oxford, United Kingdom
Coherent large-scale sea surface temperature anomalies in the Atlantic are present in the observed record on interannual to decadal timescales and often linked to the large-scale meridional overturning circulation. Yet, the underlying mechanisms of the low-frequency variability are poorly understood, including the relative contributions of atmospheric forcing and the ocean circulation. Using observations of ocean temperature and atmospheric pressure anomalies in the Atlantic basin from 1871 to 2013 and a suite of numerical experiments, we reconstruct the observed variability in the North Atlantic using a statistical multivariate regression model. The relative roles of ocean and atmospheric dynamics on the Atlantic variability and on its predictive skill are highlighted as function of the different timescales. For example, the role of air-sea coupling, via the North Atlantic Oscillation, is shown to increase the predictive skill in the North Atlantic on interannual timescales while the imprint of large-scale overturning circulation onto surface variability is shown to emerge on decadal timescales.