Nonetheless, the patterns in Fig. 1.6 show that the Lindzen-Nigam model does a good job of predicting the wind anomaly pattern associated with El Niño in the tropical Pacific and warming events in the Equatorial and southern tropical Atlantic. Fig. 1.7 shows a schematic of the three-dimensional atmospheric changes over the tropical Pacific associated with El Niño. The large-scale climate anomalies that are generated over the tropical oceans will spread over many tropical continental areas. A good example is found in the typical pattern of climate anomalies in October-December during El Niño years, described schematically in Fig. 1.7. During El Niño years, warm SST anomalies are also usually found in the western Indian Ocean, which together with the cold SST anomalies in the western Pacific and warm SST anomalies in the central Pacific, drive a clear pattern of rising and descending motion, here connecting almost two-thirds of the tropical longitudes, leading to a tendency for reduced precipitation in the Maritime Continent region in the western Pacific, and increased precipitation in the western Indian Ocean and extending into the Greater Horn of Africa. It should be noted that if the Indian Ocean pattern of SST anomalies is not observed, then the resulting atmospheric anomalies in El Niño years from the western Pacific to Africa can be very different.

A further factor tends to tie large-scale vertical motion in the atmosphere to high SST. Warmer air can hold more moisture and this tends to lead to a higher moisture content of the near-surface atmosphere over high SST. As described above, when air rises, cools and condenses moisture, there is a release of heat that makes the air more buoyant and want to rise further. If air contains more moisture, this feedback buoyancy effect can be stronger. Under this scenario, it can be argued that the locations of areas of rising motion, make a contribution to driving the near-surface winds. The exact balance of importance of this effect compared to the Lindzen-Nigam effect is still being debated and may vary according geographical location. It is interesting that, in general terms, both effects lead to near-surface winds converging over warm SST.