PACIFIC ATMOSPHERIC OCEAN COUPLING

Coastal and Trade winds. (Normal conditions)

1-Trade winds off the coast of South America and The westward winds along the equator push the warm water (heated by the sun) off to the west, drawing up the thermocline and exposing the cooler water underneath in the east. This upwelling cools the eastern surface water, a complete Walker cell.

2. The thermocline is the boundary between the cold deep water (that extends to the bottom of the ocean and around the world) and the warmer upper layer. In the tropics it forms a relatively sharp boundary. The trade winds, in piling up warm water in the west, make a thick (150 meter) warm layer in the west that pushes the thermocline down in this region, causing it to rise in the east (Upwelling). The shallow (30 meter deep) eastern thermocline allows the winds to pull up water from below, water that is generally much richer in nutrients than the surface layer. (This is so because life lives mostly in the sunlit zone. Available nutrients there are then quickly taken up by (plankton) in turn fish feed on the Plankton. Debris from the living creatures rains down into the lower layer, where nutrients dissolve, making the deep water rich, so that wherever there is upwelling, there is abundant life.) Which in turn is crucial to the economy Globally.

3. The rising air over the western Pacific is associated with rainfall (Monsoon).When air rises it cools, and can hold less evaporated water. The water falls as rain. But in returning to a liquid state, it releases the heat that was used to evaporate it from the ocean surface (heat that came from the sun), and this middle atmosphere heating amplifies the rising motion. This is a principal mechanism for heat from the sun to warm the atmosphere (the atmosphere by itself is relatively transparent to solar radiation).

4. Because the warm pool pumps great amounts of heat and moisture into the upper atmosphere (Adiabatic cooling), the system is one of the major driving forces of world climate. The huge source of heat helps set the path of the jet streams (storm tracks) that control temperate-zone weather, much as a large rock in a stream determines the pattern of water flow, including wavy motions that extend well downstream of the rock. Therefore, when the warm pool changes shape or position, the effects ripple outward to affect much of the world's weather.

El Nino Changes in pattern.

1. Suppose a relatively brief opposing wind occurs over the west Pacific warm pool. It may last for as little as one month. This starts an eastward current that pushes the warm pool a little bit east of it's usual position. If the ocean and atmosphere were not coupled, then this motion would soon stop when it ran into the trade winds. The trade winds exist because of the temperature contrast between east and west. If the central Pacific is warmed by flow from the west, even a small amount, then the region of rising air will tend to move east with the warm water. That means the trade winds will also shrink back east a little, since those winds are caused by the rising air. But then the pressure of the trades holding up the sea surface slope to the west is weakened, and even more west Pacific water tries to move eastward. That warms the central Pacific a little bit more, and the rising air moves further east- the trade winds shrink more. This collapse continues until the water is warm across the Pacific, the trades are weak, and the thermocline and sea surface slope flatten out. That is El Niño !!.

IPO (interdecadal Pacific Oscillation)

Other Ocean feedbacks can be observed in the Pacific North- Central and South west, the IPO can be a good indicator of SST's (Sea Surface Temperatures) in 3 key areas mentioned above.

Below is an example of the TRI-Pole IPO, why called tri-Pole? Simple answer- 3 key areas

The following are IPO index during 2 separate events.

We can also see the inverse connections with IPO and SOI (SOUTHERN OSCILLATION INDEX). again another observation during the onset of ENSO (El Nino southern Oscillation).

Onset of La Nina (SOI Positive)

El Nino (SOI Negative)

NOW we have several Pacific based index to make observations.

1..IPO

2..SOI

3..Nino regions 4-3-3.4-1.2

It is also notable that during FULL onset of ENSO state, effects in the uppermost North Atlantic prevail. La Nina Warm- El nino Cold -the opposite effects seen in the Equatorial Pacific.

Obviously these indexes require further analysis over several decades.