A numerical investigation of the remote influence of Pacific ENSO on variability in the tropical Atlantic Ocean

The objective of this study is to investigate the remote influence of the El Niño-Southern Oscillation (ENSO) on Tropical Atlantic Variability (TAV) via dynamical and thermo-dynamical processes. By dividing the surface wind-stress and heat flux forcing into a remote and local part, a suite of numerical simulations has been conducted using an eddy-permitting version of the latest Geophysical Fluid Dynamics Laboratory (GFDL) Modular Ocean Model (version 3) (MOM3).; These simulations yield several important findings about the role of ENSO in forcing TAV: (1) From strictly an oceanic prospective, the ENSO-induced response explains approximately 10–15% of total variance in the upper ocean thermal variability in the entire tropical Atlantic Ocean with an appreciably larger explained variance (about 25%) in the North Tropical Atlantic region. (2) Dynamics that are responsible for ENSO-induced sea surface temperature (SST) variability in the tropical Atlantic vary geographically. In the North Tropical Atlantic, the ENSO-related interannual SST variability is primarily caused by surface heat flux forcing, whereas in the equatorial and south Atlantic dynamical ocean response to change in the winds contributes significantly to the SST variability. (3) In contrast to SST, heat content anomalies over the tropical Atlantic basin can be entirely attributed to the wind-driven ocean dynamical response. The heat content anomalies in the North Tropical Atlantic appears to be dominated by variability on decadal timescales, whereas the anomalies in the equatorial and South Tropical Atlantic seems to have a significant interannual component, indicating that the cause of these different responses may reflect the difference of the oceanic adjustment processes between the north and south tropical Atlantic ocean. It is suggested from the simple subsurface model that the decadal subsurface variability in the northern tropical Atlantic is associated with the stochastic resonant frequency determined by the westward baroclinic Rossby wave speed and the characteristic length scale of the wind forcing pattern.