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Normal, El Niño and La Niña conditions. - Coggle Diagram
Normal, El Niño and La Niña conditions.
Normal conditions in the Pacific Ocean
The surface winds over the Pacific Ocean (known as the trade winds) blow towards the warm water of the western Pacific, off the coast of Austria and Indonesia.
Rising air occurs at this location as a result of water heating up the atmosphere. The trade winds across the surface of the Pacific push the warm water westwards from Peru to Australia.
In the eastern Pacific, off the coast of Peru, the shallow position of the thermocline allows winds to pull up water from below. The thermocline is the point at which the temperature changes from warmer surface waters to deeper, colder water. It is this that creates those optimum conditions for fishing, which have already been mentioned, as there is an abundance of phytoplankton within the cold water, supplying the fish with food
As a result of the pressure of the trade winds pushing the water westwards, the sea levels in the Australasia are about half a meter higher than Peru, with sea temperatures 8 degrees C warmer.
What happens during El Niño
During El Niño, the trade winds weaken, stop or even reverse in the Western Pacific
As a result, there is more warm water over the coast of Peru leading to rising air and low pressure. the water becomes 6-8 degrees C warmer in the eastern Pacific
In Australasia, however, the water becomes cooler and there is les air rising resulting in high pressure and stable, dry conditions.
Peru would therefore experience more rainfall than normal
The piled up warmer water around Australia makes its way back eastwards across the Pacific, leading to t a 30cm rise is sea level around Peru. This prevents the usual cold upwelling
What are the causes of El Niño
Scientists continue to study the exact causes of El Niño. There is a strong interaction between the ocean and the atmosphere in the Pacific, so mush that even small changes can be enough to have a large-scale impacts across the region and cause global changes to weather ad climate.
For a brief time, seafloor heating as a result of volcanic activity became a popular theory. It was noted that two separate eruptions in the region were followed closely by El Niño events. For example, Mount Pinatubo erupted in 1991, the same year in which an El Niño event began.
A more probable cause is small changes in sea surface temperatures. This could be caused, for instance, by tropical storms in Western region of the Pacific. If they are violent enough, or last long enough, they could start the movement of warm water eastwards across the Pacific.
What happens during La Niña
La Niña refers refers to unusually cold sea surface temperatures found in the eastern tropical Pacific
A La Niña event may, but does not always, follow an El Niño event
The impacts of La Niña are the opposite of El Niño, where Australia would experience droughts during El Niño, there would be increased risk of flooding during La Niña
Likewise, Peru could experience droughts during La Niña
La Niña could also be described as a more exaggerated version of a normal year in the Pacific Ocean