El Niño: Hot Air over Hot Water

H o t A i r o v e r H o t W a t e r

In the 1500s, fishermen who lived in South America began to wonder about a current of unusually warm water that came to their shore every few years near Christmastime. Since the fishermen believed in the birth of the Christ child at Christmas, and since they spoke Spanish, they named the hot water El Niño, which means "the infant" in Spanish.

Where do scientists look for El Niño? The hot water usually comes first to the coasts of Peru and Ecuador in South America.

But if we've known about El Niño for four hundred years, why is everyone talking so much about the hot water this year?

The 1997-1998 El Niño may or may not be stronger than ever before. Scientists are still deciding. One thing that is definitely different about this El Niño is the technology that scientists are using to study it.

Scientists and governments from around the world—United States, France, Japan, Korea and Taiwan—are sharing knowledge and funding for The Tropical Atmosphere Ocean (TAO) Array.

But why all the fuss anyway about some hot water in the tropical Pacific Ocean? Well, it's not just the hot water. It's also the hot air.

Try this: take two cups that are the same. They can be ceramic, plastic, styrofoam, whatever, as long as they're the same. Fill one with cool water. Fill the other with hot water. (Not boiling, just good and hot.) Place them on a table. Hold each of your hands over one cup and feel the difference in the air above the water. (Don't actually touch the water. Just feel the air.) The hot water warms the air above it. The cool water doesn't.

Now, imagine you fill your bathtub with hot water. Think about how warm and steamy the air in the bathroom gets. Now, imagine millions and millions of bathtubs-ful of hot water. All of that moist, hot air has to go somewhere. Scientists know that hot air rises and carries the moisture with it. Once the moisture gets into the air and starts to cool, rainclouds start to form.

Now try this: hold a small mirror over the cup of hot water for a few minutes. The moisture in the air should collect on the mirror, and, as it cools, form tiny droplets. Imagine the bathroom mirror after you fill the bathtub with hot water. The "water" on the mirror is caused by the water vapor in the air gathering and cooling. Now imagine the air over the hot water of the tropical Pacific Ocean. Huge rainclouds start to form and flooding results in South American countries along the coast.

It's not quite that simple, but the science of El Niño does start with those basic ideas about hot air over hot water.

Today's hot air over hot water is available online. Keep track of the latest science reports.

More general background information about El Niño is available.