BOULDER, Colo. -- While Texans swelter in a killer heat wave, and many Americans ask what's going on with the weather, atmospheric scientists from 14 countries are gathered here this week in an attempt to figure out where the world's climate gyrations are headed next, and why.

They couldn't agree on the cause of the persistent scorcher in Texas. But they do seem to agree on two things:

First, the great El Nino event of 1997-1998, a record warming of the eastern Pacific Ocean blamed for a yearlong drumbeat of storms, droughts, fires, floods, tornadoes and epidemics around the world, is over.

Second, El Nino has been replaced by an abnormal cooling of the same Pacific waters. If it persists into 1999, it will win official recognition as a "La Nina" event, with impacts in many places just the opposite of El Nino's during the coming year.

"We all believe La Nina is coming," said James O'Brien of Florida State University.

And in the wake of a strong and well-publicized El Nino, La Nina promises to make weather news around the world. But what will the headlines say? Nobody is sure.

"We're here to try to gather our thoughts about what we know and don't know about La Nina not to come out with a forecast," said Michael H. Glantz, a senior scientist at the National Center for Atmospheric Research. NCAR is playing host to this week's meeting, billed as "A La Nina Summit," and the first international scientific meeting on La Nina.

The goal is to "get a better picture of what it means to have a La Nina year," he said. Better understanding and public awareness, scientists believe, should help win more research money, leading to the development of more accurate forecasts.

And thatcould eventually help people and political leaders around the world plan for La Nina's impact on individuals and the economy.

If you have never heard of La Nina, it's not surprising.

El Nino has devastated Peru's coastal fisheries for centuries, beginning around Christmastime every four to seven years. Its name -- Spanish for little boy -- is a reference to the Christ child. It has been a topic of scientific interest for 100 years. That's almost entirely due to its damaging impact, although it can also bring some communities mild winters, relief from hurricane threats, replenished water supplies, better crop yields and improved fish catches.

La Nina's 'cold phase'

On the other hand, La Nina has received relatively little scientific study. Scientists have not agreed yet on a standard definition that might signal when a La Nina has begun.

Its name -- Spanish for little girl -- was simply one scientist's attempt at gender symmetry when he first described the phenomenon in a book in 1985. A few have suggested "El Viejo" -- the old man -- or "anti-El Nino."

Most, however, refer to El Nino simply as the "warm phase," and La Nina as the "cold phase," of the same ocean phenomenon.

El Nino, at least since the mid-1970s, has also been more frequent than La Nina, occurring nearly twice as often, and with increased severity. The most recent La Nina was 1995, and a stronger one occurred in 1988 (a year that saw devastating drought in the Midwest).

Scientists are deep into a debate about whether the tilt toward more frequent and severe warm events in the Pacific is a consequence of global warming, and whether that warming is fueled by human activities or natural cycles with periods measured in decades or more.

The latest El Nino -- perhaps the strongest of this century -- has been fading for months as east-to-west trade winds across the tropical Pacific grew stronger, scientists said.

Data from satellites and ocean buoys have shown the trade winds gradually eroding the layer of abnormally warm water at the surface of the eastern tropical Pacific. That allowed a pool of colder water below it -- a layer called the thermocline -- to rise toward the surface.

Below-normal temperatures

In the past few months, it has been bobbing to the surface in a growing, continent-sized region of the eastern Pacific.

(Only a relatively small pocket of warm water -- the last remnants of El Nino -- still hugs the South American coast. That may be responsible for delays in seasonal rains in the American Southwest, scientists said. Oceanographers also suspect that the appearance of a pool of cold, oxygen-poor water that has been killing fish and shrimp in the Gulf of Mexico off the Florida panhandle since May could also be a spinoff of El Nino's influence.)

At one buoy location in the Pacific, surface temperatures dropped from 84 degrees Fahrenheit to 72 degrees in just 30 days, a rapid conversion that astonished scientists. The temperatures there are now well below normal.

"Certainly in the records we have, we have never seen anything like this before," said Mike McPhaden, of the National Oceanographic and Atmospheric Administration.

Scientists said the cooling of the tropical Pacific since the beginning of 1998 as El Nino waned may explain why the year has been so warm. All that heat had to go somewhere. Globally, the first half of 1998 has been the warmest on record, and June was the warmest single month on record.

Perhaps it's the waning El Nino, or maybe it's global warming. Perhaps it's both. Whatever the explanation, "something exceptional is going on," said Kevin Trenberth, of NCAR's climate analysis section.

The buoy data also indicate there is plenty more cold water available below the surface, an indication this La Nina will stick around into 1999. And the computer models agree.

But does the record strength of the late departed El Nino, or the speed of the changeover, or even the amount of cold water now reaching the surface of the eastern Pacific mean a record La Nina is on tap? Scientists aren't sure.

"Just because we're coming out of the El Nino of the century, doesn't mean we're moving into the La Nina of the century," said Nathan Mantua, of the University of Washington.

So what can scientists say about La Nina?

First, La Nina will have "teleconnections" -- weather impacts around the globe, just as El Nino did.

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Effects in all directions

El Nino altered the paths of jet streams and storms by pumping heat and moisture into the atmosphere, "It's like throwing a rock into a stream," McPhaden said. It sends waves rippling out in all directions, and changes the way the stream flows. "And you can think of storms as leaves in the stream."

Likewise, La Nina changes the global weather picture again by taking away that huge island of heat and moisture, and setting the jet streams and storm tracks off in new directions.

Next, those teleconnections will vary from place to place. Based on studies of past La Ninas, there have been predictions of more Atlantic hurricanes and more of them reaching shore; colder, wetter weather this winter in Alaska, the Northwest and upper Midwest; and warmer, drier weather in the Southeast.

Ever-changing atmosphere

For Maryland, there are no clear trends apparent in the statistics from past La Nina years, O'Brien said.

Finally, not every drought, or flood, or blizzard or whatever weather patterns come along in the coming year will be attributable to La Nina, scientists agreed. La Nina is a major player, but ultimately one voice in a chorus of factors acting to create weather at any given place and time.

"Even under average conditions, there are going to be extremes," said Joseph Tribbia of NCAR. "The atmosphere is a chaotic system."

Pub Date: 7/17/98