La Niña and El Niño

Is it the changes in the air or water currents that create the El Niño? Or is it perhaps the earth rotation? The question seams to be impossible to answer.

Trade winds create a slight uphill of warm surface waters to the west. With 4-8 years cycles, the trade winds get weaker and the slope slides back eastwards.

El Niño occurs at irregular intervals between 4-8 years. Opposite, La Niña, which is actually a strengthening of the normal state occurs in between. This happens when westerly trade winds are stronger and drives warm surface water westward.

With El Niño, more warm water then normal reaches the west coast of South America, This prevents the cold Humbolt current from reaching the surface along the coast which changes the whole ecosystem. Fishing is poor, coral reefs could die. On land, the normal condition is a dominant high-pressure with low rainfall as a result. During El Niño low pressures become more frequent and Chile and Peru will be hit by torrential rain(downfall). On the other hand, Indonesia and Australia's eastern parts get severe drought.

 La Niña affects the climate in the opposite way. The Humbolt current will function normally, it will be a very stable high pressure over Chile and Peru as well as strong low pressure in Indonesia and eastern Australia.