The Role of Ocean Processes with Coupled Variability in the Tropical Atlantic

The zonal mode of variability in the tropical Atlantic is often referred to as the Atlantic Niño mode because it resembles the Pacific El Niño Southern Oscillation (ENSO). Several differences between the nature of the zonal mode in the Atlantic and its counterpart in the Pacific have prompted the question: Is the role of the ocean in the zonal mode in fact similar to its role in ENSO? Although both modes of variability display a decrease (increase) in the trades associated with positive (negative) SST anomalies in the east, the oceanic processes behind these modes of variability may be quite different.

Local coupled ocean-atmosphere feedbacks in the Atlantic are weaker than they are in the Pacific and so tropical climate variability within the Atlantic is more susceptible to external influences. This remote forcing, together with the existence of another dominant mode of coupled variability, the meridional mode, means that the situation in the Tropical Atlantic is in many ways more complex. As a result of this complexity and relatively fewer studies than in the Pacific, understanding of the zonal mode is limited.

To facilitate an investigation into the role of the ocean within this inter-annual coupled mode, ROMS is used to simulate conditions in the Tropical Atlantic between 1958-2004. Preliminary results from this simulation and an investigation into the energetics of equatorial Atlantic oceanic variability will be presented. This work forms part of the first author's PhD research.