North Atlantic Multidecadal Climate Variability: An Investigation of Dominant Time Scales and Processes

The issue of multidecadal variability in the North Atlantic has been an important topic of late. It is clear that there are multidecadal variations in several climate variables in the North Atlantic, such as sea surface temperature and sea level height. The details of this variability, in particular the dominant patterns and time scales, are confusing from both an observational as well as a theoretical point of view. After analyzing results from observational datasets and a 500-yr simulation of an Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) climate model, two dominant time scales (20-30 and 50-70 yr) of multidecadal variability in the North Atlantic are proposed. The 20-30-yr variability is characterized by the westward propagation of subsurface temperature anomalies. The hypothesis is that the 20-30-yr variability is caused by internal variability of the Atlantic Meridional Overturning Circulation (MOC) while the 50-70-yr variability is related to atmospheric forcing over the Atlantic Ocean and exchange processes between the Atlantic and Arctic Oceans.