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Coupled Ocean - Atmosphere System

The magnitude as well as the spatial gradients of SSTs in turn regulate the intensity of convection because they determine the available thermodynamic energy and hence the degree of convective instability. A substantial fraction of the required moisture (to sustain the convection and the cirrus) is imported by large-scale, low-level convergence through the Walker cell from the east and the trade winds of the Hadley cell. The strength of these low-level winds is in turn partially governed by the latent heating and the radiative heating within the convective-cirrus system. Therefore, this convective-large-scale system is self-sustaining. Finally, frictionally driven motions in the oceanic surface layers by the low-level winds give rise to equatorial upwelling and other major current systems that have significant influence on the SST patterns.

The El Nino Phenomenon: A Natural Global Change Experiment

Modern-day scientific attention on interannual climate change centers around the so-called El Nino southern oscillations (ENSO) phenomenon. The entire coupled system described earlier undergoes oscillations with periods ranging from 2-6 years. The oscillation is most dramatically seen in the tropical Pacific surface pressure field and is accompanied by large variations in SST, precipitation, winds, and currents. The El Nino part of ENSO refers to the warming of the eastern Pacific surface waters.
The El Nino is accompanied by a significant migration of the deep convection regime from the western Pacific to the central Pacific. Hence, the onset and the subsequent evolution of the El Nino is identified by the anomalies in the outgoing radiation field. The anomalies can be as large at [[as?]] 100W/m^2. While the longwave flux decreases, the reflected solar flux increases by the same magnitude as shown in figure 2. In spite of these significant changes in the radiation field, their importance to the dynamics of ENSO have largely been ignored. An exciting development is that recent studies raise the intriguing possibility that these events provide vital clues into the coupling between ocean warming and radiative feedbacks. For example, during El Nino of 1987-88, the peak solar heating of the central Pacific decreased by about 50-100W/m^2, while the greenhouse effect of the atmosphere increased by the same magnitude.

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