2012 Project Summary Decadal and Multidecadal Variability of the AMOC in Observational Records and Numerical Models

The purpose of this project is to identify and investigate variables and processes that have been relatively better observed and can be associated with decadal-‐to-‐multidecadal changes of AMOC, and to examine these processes in climate model simulations. Recent Results (1) The North Brazil Current (NBC) transport, calculated from 5 decades of historical hydrographic data, exhibited a multidecadal variability. It is shown to be an useful indicator for AMOC low frequency variations. As a major pathway for surface return flow of AMOC, the NBC transport variability lags the Labrador Sea deep convection by a few years and is coherent with the Atlantic Multidecadal Oscillation (AMO) in sea surface temperature. The study suggests a need of western boundary current measurements off the coast of Brazil as a complementary component of AMOC observing system, so that the multidecadal historical record can be extended further into the future. (Zhang et al. 2011, an AGU Journal highlight) (2) While decadal variability of NBC and AMOC at various latitudes (e.g. 6°S, 26°N and 40°N) are highly coherent in coupled models, they are less so in data assimilation products. GECCO and SODA show that the AMOC at 6°S is more coherent with the AMO than the AMOC a