The North Atlantic Current (NAC) climate cycle is comprised of approximately 100 Amazon rivers, and belongs to the worldwide "salt conveyor" current that extends out to the Pacific Ocean. NAC is primarily maintained by the cyclic process of heat transfer where ocean currents that run in the North-South direction reallocate heat from the equator to more temperate zones. This redistribution of heat is further enhanced by the movement of winds. As a result, warmer currents are able to penetrate higher latitudes than usual. For instance, warm waters flow up the north from the tropical zone as the Gulf Stream (which travels eastward) merges into NAC. Europe becomes warmer during the wintertime by about 9-18 degrees Fahrenheit due to the warmer waters that flow up the Norwegian coast. The evaporation of the NAC surface waters (aided by the cold, dry winds that come from Canada in an eastward direction) causes NAC waters to leave their salt sediments behind. This results in the sinking of the dense surface waters which flow south, allowing for the "salt conveyor" cyclical process to occur. The "salt-sinking" waters therefore make room for warmer water to flow further north (which accounts for the tolerable European winters, as mentioned earlier).

When this yearly flushing of salt-laden waters halts, the "conveyor belt" is interrupted, in which the heat transfer process is unable to travel northward. And here is where the problematic issue of abrupt cooling arises. This failure of flushing is signified by the absence of cooled surface waters sinking and migrating southward while allowing warm waters to flow northward. Several explanations are brought forward: 1) decreased wind chill, 2) the presence of more floating ice, and 3) the addition of fresh water to the ocean surface. The second point of reasoning accounts for the North Atlantic Oscillation (a shift in the atmospheric-cirulatory pattern over the North Atlantic, which has commenced in 1996).

THE OCEAN: In the Pacific, the North Equatorial Current moves water from East to West along the equator, where it is warmed by the intense tropical sun. The water is then pushed North along the coast and back East at higher latitudes, where it cools down before moving South along the Eastern edge of the ocean with the Humboldt Current. As a result, the temperature of the Western Pacific is up to eight degrees Celsius warmer than that of the Eastern Pacific. At tropical latitudes, warm water is accumulated in the Western Pacific to such a great extent that there is actually a half-meter difference between sea levels in Indonesia and Ecuador. A steep East-West thermocline is created by this uneven distribution of warm water.

 

 

Normal Conditions: Surface Temperatures

In this picture of surface temperatures in the tropical pacific, you can see how warm water accumulates in the West Pacific at during a normal year. Compare with El Niño or La niña.

The Pacific Thermocline is very deep in the West and so shallow in the East that that off the coast of Peru and Ecuador, there is a nutrient-rich upwelling of cold water from below the thermocline. The upwelling is crucial to the economies of these coastal nations because it supports the fish population, the harvest of which is a big source of export revenue for these countries.

THE ATMOSPHERE: The Easterlies, also known as Trade Winds, are winds that blow from East to West parallel to the North Equatorial Current. They help move water Westward along the equator, while the Westerlies blow water eastward at higher latitudes.

There are areas of higher and lower pressure over the Pacific created by the Walker Circulation (see appendix for a picture of the Walker Circulation). The air that arrives in the West Pacific, having traveled with the Easterlies above the ocean along the equator, is very warm and moist. Because it is so warm, it rises over the West Pacific; this creates a permanent low pressure area. When the air rises, it cools somewhat, and all the moisture it is carrying condenses and falls as rain over the West Pacific coast. As the air moves back East with the Westerlies, it is cooled, and so sinks over the East Pacific, creating a high pressure region with comparatively little rainfall. Whenever the pressure on the West Pacific gets lower, the pressure on the East Pacific gets higher and vice versa; it goes back and forth from year to year and so is known as the Southern Oscillation. The Southern Oscillation is measured by the Southern Oscillation Index (SOI), which is the relative difference between the atmospheric pressures in Tahiti and Darwin, Australia.

TO SUM UP: Under normal conditions, low pressure, warm water, and heavy rains stay on the West Pacific coast, while high pressure, cold water, and dry conditions prevail on the East Pacific coast.