ENSO Neutral

During ENSO neutral conditions, surface trade winds blow westward across the equatorial Pacific Ocean. Blowing against the ocean’s surface, these winds result in a westward current.

These persistent winds and currents are responsible for sea levels in the western Pacific, for example, in Indonesia, to be up to 50 cm higher than those in the eastern Pacific, for example, in Peru.

Neutral conditions also foster upwelling of cool, nutrient-rich sea water on the northern Pacific coast of South America. This process supports a healthy marine ecosystem and promotes robust aquaculture activities. Compared to other equatorial Pacific regions, the equatorial region from South America to the central Pacific will experience relatively cool sea temperatures contributing to relatively dry conditions in that area.

During ENSO Neutral, the following conditions are likely:

• Lower Atmospheric Circulation: Towards the West- Surface air pressure is higher over the central equatorial Pacific, for example Tahiti, than the western equatorial Pacific, for example Australia. This gradient in surface air pressure results in a flow of surface air moving from higher pressure to lower pressure, or west to east.
• Surface Water Circulation: Towards the West- The lower atmospheric circulation has a direct effect on the surface water beneath it. The east to west movement of air in the lower atmosphere along the equatorial Pacific Ocean works on the water below it, resulting in an east to west current near the surface.
• Upper Atmospheric Circulation: Towards the East- The low level winds converge over the warm waters of the western Pacific and rise. The forced ascent of the very moist air creates heavy rainfall in the region, wringing the air of moisture. The now dry air diverges out of the top of the convective region, moving out over the eastern Pacific to sink over the cooler waters.
• Thermocline: Slanted down from the eastern Pacific to the western Pacific- The thermocline marks the transition between the warm upper water and the cold deep water in the Pacific Ocean. Under neutral conditions, the thermocline is slanted down from east to west across the equatorial Pacific Ocean. This allows for upwelling of cooler, nutrient rich deep water towards the surface layer in the eastern equatorial Pacific.