f the Pacific. He noticed that when pressure rises in the west it usually falls in the east and vice versa. He coined this term Southern Oscillation. When it is on its high index state pressure is high on the eastern side of the Pacific and low on the western side (figure 1). The east west pressure contrast drives easterly surface winds. When it switches into low index (figure 2) the easterly surface winds weaken. The biggest changes are over the western Pacif
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