单选题 Intensive research is yielding (产生) important insight into El Ni ? o, a periodic warming of tropical waters in the Pacific that can trigger devastating drought and flooding. Scientists are finding that the phenomenon exists in reverse; some call it La Ni ? a.
Typically El Ni ? o, like the calamitous 1982-1983 event that brought misery to places as far apart as Ecuador, Australia, and southern Africa (National Geographic, February 1984), announces itself with strong westerly winds along the Equator (赤道), accompanied by a warm current that usually arrives off western South America around Christmas, which led to its name, Spanish for "the Child". Ocean fisheries (渔业) suddenly collapse, and coastal deserts reel under torrential rains that sweep away villages.
Scientists now believe that between El Ni ? o there often are La Ni ? a: one-or-two-year periods when the surface water of the equatorial Pacific becomes cooler. Experts detected the onset of La Ni ? a in the spring of 1988, leading some to link it to last summer"s drought in the United States, flooding in Bangladesh, and the abnormal cold winter in Alaska and western Canada.
The early detection of El Ni ? o and La Ni ? a is an invaluable tool for long-range weather forecasting.