1. El Niño: A temperature anomaly

2. An Introduction
Fishermen of the Pacific off the coast of Peru and Ecuador have known for centuries about the El Niño.
Every three to seven years during the months of December and January, fish in the coastal waters off of these countries virtually vanish, causing the fishing business to come to a standstill.

3. History and impact
South American fishermen have named this phenomenon El Niño, which is Spanish for "the Boy Child," because it comes about the time of the celebration of the birth of the Christ Child. During an El Niño, , the physical relationships between wind, ocean currents, oceanic and atmospheric temperature, and biosphere break down into destructive patterns that are second only to the march of the seasons in their impacts to weather conditions around the world.

4. Normal Conditions (Non El Nino)
In the tropical Pacific, winds generally blow in an easterly direction
These winds tend to push the surface water toward the west also. As the water moves west it heats up even more because it's exposed longer to the sun.
Meanwhile in the eastern Pacific along the coast of South America an upwelling occurs. Upwelling is when colder water from the bottom of the ocean moves up toward the surface away from the shore.

5. Strong trade winds blow from the east along the equator, pushing warm water into the Pacific Ocean.

6. Normal conditions contd
In the east the water cools the air above it, and the air becomes too dense to rise to produce clouds and rain
However; in the western Pacific the air is heated by the water below it, increasing the buoyancy of the lower atmosphere thus increasing the likelihood of rain. This is why heavy rain storms are typical near Indonesia while Peru is relatively dry

7. El Nino conditions
El Nino happens when weakening trade winds (which sometimes even reverse direction) allow the warmer water from the western Pacific to flow toward the east
This flattens out the sea level, builds up warm surface water off the coast of South America, and increases the temperature of the water in the eastern Pacific.

8. El Nino: weakened trade winds in the western Pacific near Indonesia
El Nino: weakened trade winds in the western Pacific near Indonesia. Warm water flows toward South America.

9. Effects of El Nino
Clouds and rainstorms associated with warm ocean waters also shift toward the east.
rains which normally fall over the tropical rain forests of Indonesia fall over the deserts of Peru, causing forest fires and drought in the western Pacific and flooding in South America.

10. Effects continued….
Earth's atmosphere responds to the heating of El-Nino by producing patterns of high and low pressure which can have a profound impact on weather far away from the equatorial Pacific.
For instance, higher temperatures in western Canada and the upper plains of the United States, colder temperatures in the southern United States. The east coast of southern Africa often experiences drought during El Nino.

11. Atmospheric effects of El Nino