Indirect Wind-Forcing of the Atlantic Meridional Overturning Circulation

Thursday, 18 December 2014: 9:15 AM
Eleanor Frajka-Williams, University of Southampton, Southampton, SO14, United Kingdom, Richard G Williams, University of Liverpool, Liverpool, L69, United Kingdom and Aurelie Duchez, University of Southampton, Southampton, United Kingdom
Recent observations of the MOC at 26N from the RAPID/MOCHA array have shown a downturn in 2009/10 and a longer term decline, from 2004--2012. This downturn was reproduced in an atmosphere-forced numerical model (Roberts et al., 2013) without data assimilation, and in a simple two-layer model (Zhao and Johns, 2014). We will show that this variability of the MOC---both the reduction in 2009/10 and the longer term decline---can be traced back to wind-forcing. While the direct wind-forcing associated with local Ekman anomalies at 26N contributes, the primary source of interannual variability stems from Ekman convergence over the subtropical gyre. These combined effects of the wind on the oceanic transport explain the majority of the interannual variability of the observed MOC at 26N.