El Nino Exits, but La Nina Waits in Wings
The good news is that--after billions of dollars in damage and hundreds of lives lost throughout the world--El Nino is finally over. The bad news is that La Nina apparently is on the way.
El Nino, the intensely studied, yearlong oceanographic and meteorological phenomenon characterized by a dramatic rise in surface sea temperatures off the west coasts of North and South America, hammered California with powerful storms that did more than $550 million in damage and claimed at least 17 lives across the state.
La Nina, El Nino’s less publicized flip side, is characterized by a dramatic drop in sea temperatures and could bring just the opposite next winter--drier than normal weather in California and a punishing drought from the Rockies to the Midwest.
Early predictions about the effects of the 1997-98 El Nino--among the first ever offered by the federal government--often proved uncannily accurate.
Ants Leetsmaa, director of the National Atmospheric and Oceanographic Administration, warned in October that Southern California faced powerful, long-lasting storms during the winter that would be comparable to the devastating deluges here in the El Nino winter of 1982-83.
“The southern part of the state is expected to have rainfall in the order of 200% of normal,” he said.
Leetsmaa was right--overall, Southern California recorded 231% of the normal rainfall. But there was a little luck involved.
Scientists have learned that although weather is largely governed by major cycles like El Nino and La Nina, it also is affected by random events, even things as seemingly trivial as a sea gull’s decision to swoop to the left instead of the right.
“We are more and more aware that it’s a probabilistic system, not a completely deterministic system,” said Nicholas Graham, a meteorologist with the International Research Institute for Climate Predictions at the Scripps Institution of Oceanography in La Jolla.
“We’re up against a chaotic process,” he said. “We’ll never be able to say exactly how much it’s going to rain on a given place in a given winter.”
Because random events can skew the complex calculations of even the most sophisticated computer, meteorologists are talking primarily in general terms about what next winter is likely to bring.
Satellites and sensor buoys show that surface water temperatures have dropped dramatically off the coast of South America in recent weeks, an occurrence that frequently presages La Nina.
“What’s happened thus far is typical of La Nina,” said John Christy, an associate professor of atmospheric science at the University of Alabama, Huntsville.
“La Nina is coming on strong,” said Michael R. Smith, a meteorologist who is president of WeatherData Inc., a firm that provides forecasts for The Times.
If these scientists are right, and La Nina is beginning to build, we’ll probably get more of those dry, offshore Santa Ana winds than normal next winter.
“There would be less humidity than normal, and although some days might be warm, some of the minimum overnight temperatures could be quite cold,” Graham said. “There’s a tendency for lower-than-normal precipitation in Southern California.”
Agreeing with Graham, Smith went further, saying the combination of an apparent La Nina and a period of reduced sunspot activity promises to intensify an already developing drought in the country’s midsection.
“Drought conditions and above-normal temperatures are already present and are expected to continue for the remainder of 1998 and into 1999 in many regions of the United States,” Smith said.
Since May 1, San Antonio has received only 12.8% of its normal rainfall, and Wichita, Kan., has received just 27.7%.
Smith said that although La Nina’s effects on weather are pretty well understood, the connections between diminished sunspot flare-ups and drought in the nation’s midsection are primarily statistical, with data showing a link stretching back almost 300 years.
“I can only speculate that it has something to do with changes in [solar] radiation and shifts in the sunspots’ magnetic polarity,” Smith said.
Both Smith and Graham stressed that unforeseen factors could crop up at any time, diminishing the accuracy of any long-range forecasts.
“Mother Nature doesn’t know exactly what’s going to happen this winter because, in a very real sense, that has not yet been determined,” Graham said. “If a bird turns left instead of right, that changes things, and after two or three weeks, things will really be different.”
Meteorologists explained that this random shift in a bird’s path could set up a tiny ripple of air that, by chance, might be reinforced and deflected by another ripple, and then another. Eventually, as atmospheric systems shift constantly to maintain an exquisite balance, the swirling ripples could evolve into an immense, rotating storm system that could affect weather for a while over a vast area.
Christy stressed, however, that virtually all random perturbations simply die out on their own and that, overall, major cycles like El Nino-La Nina tend to prevail.
Although El Nino is a Pacific Ocean phenomenon, the 1997-98 event was one of the most severe on record, and its effects were felt worldwide.
In Indonesia, extreme drought helped devastate an already crippled economy, exacerbating a political crisis. Wildfires blackened more than a million acres of forest there, throwing up palls of blinding smoke that were blamed in a jetliner crash on Sumatra that killed all 234 on board.
Destructive floods ravaged normally arid foothills in Ecuador, Chile and Peru. Dry weather dropped the levels of the normally rain-swollen Panama Canal, limiting the draft, and hence the cargo loads, of ships using the waterway.
For one of the few times on record, snow fell in the Mexican city of Guadalajara. There were fewer hurricanes than usual in the Caribbean and along the East Coast, but more tornadoes than usual in Florida. That state also suffered from an unusual drought, permitting the rapid spread of wildfires that, in some areas, continue to burn.
El Nino pounded California with a vengeance, deflecting jet-stream winds to funnel repeated storm systems into the state. The impact on California was great, multifaceted and complex.
Heavy rain--including the fading remnants of a hurricane--deluged the valleys, validating predictions that much of the state would get twice as much precipitation as normal. In Los Angeles, the total for the season--which runs from July 1 through June 30--was 31.01 inches, compared with a normal 15.11. In San Francisco, they got 47.22 inches, compared with a normal of 20.52.
Floods and mudslides damaged or destroyed hundreds of homes, businesses, roads and public structures in California. Gale-force winds tore off roofs, felled trees and dropped power lines.
Excessive rains and lack of sunshine devastated crops, including cotton, lettuce, artichokes and strawberries. Mosquitoes, ticks and other pestering insects abounded.
Rodents flourished, along with the coyotes and rattlesnakes that feed on them. Chaparral in former burn areas grew vigorously, which means more fuel for brush fires this fall. Runoff poured pollutants into lakes and the ocean, which meant more closed beaches but also more nutrients for future generations of fish to feed upon.
Finally, a few days ago, scientists said the most studied El Nino in history was over.
In the same breath, they said La Nina probably was beginning. That’s because the two phenomena are closely related.
Graham explained that the Pacific is essentially one vast basin, “with the water sort of sloshing back and forth.”
During normal conditions, equatorial trade winds blow from east to west, shoving water ahead of them that tends to pile up near Indonesia, raising the sea level there a foot higher than it is along the coast of Peru. During El Nino, the trade winds slacken or even reverse altogether, and the water sloshes back toward the west coast of South America.
The sloshing surface water presses down cooler water beneath it that normally wells to the surface off Peru. As a result, the surface water stays warmer than normal, and begins ebbing back westward across the Pacific.
The vast pool of warm surface water--often illustrated on television during the past year as a red-and-white swath spreading westward from Peru--interacts with the air above it to disrupt normal weather patterns.
Fortunately, Graham said, El Nino also sets up ocean and wind currents that ultimately--usually within a year--reverse the phenomenon.
“An El Nino ends up digging its own grave,” he said. “If it didn’t, we’d just get stuck in one.”
In some years, however, the reversal goes beyond normal, and the surface water off the coast of Peru becomes unusually cool. That’s La Nina, which apparently is starting to build now.
The colder water--like El Nino’s warm version--interacts with the air above to produce unusual weather.
Graham said that if the burgeoning La Nina blossoms as expected, its effects could be felt across much of the world this winter.
Conditions would be wetter than normal in the U.S. Northwest, cooler than normal in the north-central states, and warmer in the South. More hurricanes than usual would be expected along the East Coast, and more tornadoes than normal would plow through the Midwest.
It would be wetter than usual in the northern part of South America and drier than normal in the southern part. Indonesia, which suffered a crippling drought during El Nino, could expect heavier than normal rain.
In California, where reservoirs already filled to capacity would offset a drier-than-normal winter, La Nina would generally be less dramatic than the recently ended El Nino.
RAINFALL CHARTED: A look at the past 121 years in L.A. area rainfall. B2
(BEGIN TEXT OF INFOBOX / INFOGRAPHIC)
Impact of El Nino
Precipitation at selected Southern California stations during the recently concluded 1997-1998 rainfall season.
*--*
Reporting station Season’s total % of normal San Luis Obispo 43.98 inches 187 Pismo Beach 34.80 inches 214 Lompoc 37.25 inches* 267 San Marcos Pass 73.87 inches** 277 Santa Barbara 46.99 inches* 277 Ojai 48.68 inches* 235 Ventura 42.70 inches* 298 Oxnard 37.84 inches 263 Thousand Oaks 39.85 inches 259 Chatsworth 44.19 inches* 264 Northridge 36.10 inches* 244 Burbank 37.09 inches 234 UCLA 43.55 inches* 256 Culver City 31.39 inches* 240 Civic Center 31.01 inches 210 Pasadena 39.17 inches 202 San Gabriel 37.81 inches 211 Anaheim 31.43 inches 215 Santa Ana 30.65 inches 250 Newport Beach 28.04 inches* 258 Riverside 21.41 inches 214 Idyllwild 45.01 inches 172 Oceanside 20.01 inches 183 Palomar Mountain 53.09 inches 189 San Diego 17.78 inches 180
*--*
* record total
** highest total in Southern California
Source: National Weather Service
