A dipole pattern of the sea surface height anomaly in the North Atlantic: 1990s-2000s

Abstract

Despite a long-term trend of sea level rise continuing into the 2000s in the subpolar North Atlantic, variations in the sea surface height have behaved differently in both spatial and temporal domains. A dipole pattern, centered between the Northern Atlantic subpolar region and the region near the Gulf Stream, was observed in the linear trends of the sea surface height anomaly (SSHA). By applying the Ensemble Empirical Mode Decomposition (EEMD), we found that this dipole pattern is mainly associated with the interannual to decadal SSHA oscillations of the two regions, which are 180 out of phase with each other over the time span of this study. The low-frequency variations of the SSHA in the subpolar region are strongly inversely correlated with the cumulative North Atlantic Oscillation (NAO) index (r =-0.84), in contrast with the Gulf Stream region, which is positively correlated (r = 0.22). This therefore reveals an asymmetric response of the regional SSHA to the cumulative NAO-forcing, in which the subpolar variability leads that of the Gulf Stream region by 29 months. Moreover, there is a remarkable reversal of the SSHA trends from the 1990s to the 2000s, which is unexpected given a weak and fluctuating NAO behavior since mid-1990s. Such SSHA variations in the 2000s might be related to the lagged variations of the Atlantic meridional overturning circulation (AMOC). © 2012. American Geophysical Union. All Rights Reserved.