El Niño did not receive its name from a meteorologist or an oceanog- rapher but from Peruvian fishermen who periodically observed the ap- pearance of warm waters off the coast of Peru. The fishermen called these warm currents "Corriente de El Niño," or "Current of the Christ Child," because they usually occurred around Christmas.

During El Niño, the upper ocean waters of the tropical central and eastern Pacific Ocean warm up above normal, strongly and extensively. The warmer waters heat the air above them, increasing the buoyancy of the lower atmosphere,in turn producing clouds and heavy rains. But the air over the cooler western equatorial Pacific Ocean becomes too dense to rise to produce clouds and rain.

La Niña is like...