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After Three Strikes, Is La Niņa Out? NASA Public Affairs, March 6, 2001 La Niņa-like conditions that have persisted in the Pacific Ocean for three years might finally subside this Fall. The change could pave the way for a weak El Niņo -- and a surge of hydroelectricity for power-starved California. Last autumn scientists thought La Niņa had faded, but recent NASA satellite images reveal La Niņa-like conditions lurking in the Pacific for the third year in a row. Will they linger for a fourth? Some computer climate models predict La Niņa will vanish in 2001 and that a weak El Niņo could take its place. A shift from La Niņa to El Niņo conditions would likely trigger more rainfall in California, where swelling rivers will increase the output of hydroelectric dams, providing the state with some much-needed electricity. Over the next few months, scientists plan to monitor the situation using data from several satellites -- including the NASA-French TOPEX/Poseidon spacecraft -- to see if the La Niņa pattern of Pacific sea surface temperatures remains or departs. Northern spring is a crucial time for such monitoring. "It's almost like it's a new ball game every year between March and May," said John Wallace, professor of atmospheric science at the University of Washington. "That's when (the Pacific) sort of forgets what it's been doing and decides what it's going to do next year," If La Niņa wanes, an El Niņo could begin in the fall. But if it does, it won't be like the Super-El Niņo of 1997 and 1998. The next El Niņo is likely to be mild. "Because we've just had a big El Niņo, it's very unlikely that we'd have another big one this year. The big El Niņos tend to be separated by weaker ones," said Vernon Kousky, a research meteorologist with the National Oceanic and Atmospheric Administration's Climate Prediction Center. The return of El Niņo would mean more rain in California and in the Southeast U.S., cooler temperatures in the Southwest U.S. and generally warmer temperatures along the west coast of Canada and Alaska. El Niņos recur every 4 years on average -- and this fall marks 4 years after the onset of the last one -- but the time between El Niņos varies widely. "The period ranges anywhere from as short as 2 years to as long as 7 years," Kousky said. "El Niņo" and "La Niņa" are names for the two extremes in a huge, slow-moving, natural oscillation of the tropical Pacific Ocean. During a La Niņa phase, strong winds blowing from east to west along Earth's equator push surface waters toward Southeast Asia. Deep, cold water wells up in the eastern Pacific near South America to replace water that's blown westward. The upwelling forms a streak of cold water across the eastern half of the equatorial Pacific, a telltale signature of La Niņa conditions. When the cycle switches to an El Niņo phase, the winds die down, the upwelling weakens, and the eastern Pacific becomes warmer than usual near the equator. Scientists hope to figure out what the Pacific will do this year by running computer simulations. "Some computer models ... indicate that we might get a weak (El Niņo) by the end of this year; others say we won't until next year," Kousky said. Which of these two scenarios plays out depends, in part, on another larger-scale fluctuation in the Pacific called the "Pacific Decadal Oscillation" (PDO). The PDO is a pattern of sea surface temperatures similar to El Niņo/La Niņa, but different in that it fluctuates over decades instead of years. It's also much larger. Some researchers liken it to a swollen version of El Niņo or La Niņa. The PDO has a positive phase and a negative phase. The positive phase resembles El Niņo -- a warm "wedge" of water around the equator surrounded by a cool "horseshoe" to the north, west, and south. In the negative phase, which resembles La Niņa, the temperatures are reversed. The negative phase of the PDO is so much like La Niņa that researchers aren't entirely sure which we're experiencing now. It matters little, however, since the short term climate effects are similar. "The present 'cool' or 'negative' phase of the PDO looks a lot like and tends to produce impacts similar to the La Niņa of the past two winters and springs," says William Patzert of NASA's Jet Propulsion Laboratory in a recent press release. "The big debate among climate scientists is whether we are entering a long-lasting negative PDO episode." During the negative phase of the PDO, El Niņos tend to be weaker and less frequent. Since 1976, the PDO has been in a positive phase, which tends to favor strong El Niņos. But now the PDO may be switching back to the negative part of its cycle. If so, the upcoming El Niņo is likely to be weak. Climate scientists caution that it's too early to tell if the PDO has really switched. "I think [we won't] know except with the benefit of hindsight. ... It's kind of like people commenting on the stock market after it's already happened," Wallace said. Only time will tell if this year's La Niņa-like ocean temperature pattern will vanish. Meanwhile, western power consumers might well cross their fingers and wish it gone. After all, a bit of El Niņo-like weather might prove to be a welcome change for California's beleaguered utilities.
And ye shall know the truth, and the truth shall make you free.
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