1. El Nino

2. Why Does It Rain ?
Water vapor condenses,releasing latent heat causes air to rise, cool, and lose more water vapor.
Rising, expanding air creates an area of relatively high pressure at the top .
Air flows out of high-pressure zone towards areas of low-pressure.

3. La Nina, El Nino or the Southern oscillation:
A pool of warm surface water most of the years is held by the equatorial trade wind between Indonesia and the South America and moves this current westwards towards Indonesia.
Every 3-5 years the low-pressure system breaks in Indonesia.
This giant pool of warm water moves backward and forward between Indonesia and S. America, this effect is called EL Nino.

4. El Nino Southern Oscillation
Large pool of warm surface water in Pacific Ocean moves back and forth between Indonesia and South America.
Most years, the pool is held in western Pacific by steady equatorial trade winds.
Every three-five years the Indonesian low pressure system collapses and the mass of warm surface water surges back east.

5. El Nino Southern Oscillation
During an El Nino year, the northern jet stream (normally over Canada) pulls moist air from the Pacific over the U.S.This is accompanied by intense storms and heavy rains (from California across the midwest States).
The counterpart to El Nino is La Nina when the eastern tropical Pacific cools down.
During intervening La Nina years, hot, dry weather is often present (California to midwest)
Together these cycles are called El Nino Southern Oscillation (ENSO)

6. El Nino Southern Oscillation