Jet Propulsion Laboratory weather researcher Bill Patzert says the origins of the recurring phenomenon such as El Nino and La Nina can be explained by looking at the heat generation and storage of Planet Earth.

"The tilt of Earth means that the tropics more directly face the sun and constantly gain heat over the year," he said. "The polar regions lose heat because during the winter they get no direct sun. Nature uses the atmosphere and the oceans to redistribute the heat of the tropics to the poles. Without that redistribution, the tropics would get hotter and hotter and the poles would get colder and colder."

TALKING EL NINO: JPL researcher Bill Patzert has been studying El Nino and other episodes in nature and offers a little background on their causes.

There is a balance of redistribution, about half coming from the circulation of the atmosphere and about half coming from the ocean, he said.

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But year to year, decade to decade, slight imbalances occur in how heat accumulates.

"Mother Nature has an answer for that," Patzert said. "She creates 'episodes' to help the planet catch up on heat redistribution. El Nino and La Nina are examples of that. As scientists, what we have learned is that you can see those episodes coming and once you do, it can't be turned around. You can forecast the impacts months in advance, but you can't change what's going to happen."

The episodic El Nino and La Nina events have been labeled the "El Nino Southern Oscillation" or ENSO by scientists who study how the periodic changes occur.

Patzert said that in the normal pattern, trade winds blow from west to east from the Americas to Asia, moving the warmest water of the tropics toward the coast of Asia. Satellites can measure this "piling up" of water by measuring the height of the surface of the ocean and the temperature of the water.

During an El Nino event, the trade winds die down or even reverse, allowing the warm pool of water from the equator to move to the west, piling up against the coast of Central and South America.

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The change in where the ocean is warmest causes a change in where the most water vapor rises into the atmosphere and where the powerful winds of the jet stream are positioned.

How dramatic the changes are depends on how much warmer than normal the water becomes. The strength of the episode is measured by gauging how much above normal ocean height the warm water rises.

The current El Nino, officially declared last spring, has a 90% of chance of lingering at least through May, Patzert said and is one of the strongest on record.