Creating super weather forecasts

Tropical Storm Dennis is shown off the North Carolina coast in this National Oceanographic and Atmospheric Agency satellite image August 31.

Sept. 2 —  Scientists have found that by combining various computers, they can create one super weather forecast. The system, which is still being tested, has shown promising results so far in detecting the path of hurricanes and may be used in the future to fine-tune the science of forecasting.

THE FLORIDA STATE University researchers combined forecasts produced by computers around the world into what they call a “superensemble” that produces results that are better than the sum of its parts.

“We are seeking to demonstrate to the weather community that it can do so well it can become a useful product in the future,” said project leader T. N. Krishnamurti in Friday’s edition of the journal Science. Krishnamurti developed the idea in January.

The system is being tested during the ongoing 1999 hurricane season and so far it is doing really well, said Eric Williford, a research scientist at Florida State.

For example, 11 different computers were used to analyze the hurricane season and forecasters could tell right away that Hurricane Dennis, the latest Atlantic hurricane, would keep away from the Carolina coast.

In a three-day forecast of hurricane wind strength, the margin of error for individual computers ranged from 31.3 mph to 32.4 mph. But the “superensemble” margin of error was only 21.5 mph.

But what happens when the computers don’t agree? That was the case in 1998, when Hurricane Mitch devastated Honduras.

“When the models do well, we do a little better but when everyone’s wrong, we’ll be less wrong,” said Williford.

Williford said researchers have used the team computer approach to test 90 cases and said there were promising results in fine-tuning measurements of both the track of hurricanes and of their intensity.

COMPUTER MODELS

Computer models are massively complex programs that use mathematical formulas to describe how the atmosphere works.

Millions of readings of wind direction and speed, temperature, pressure, humidity, light, cloud cover and other variables at different altitudes are collected around the world and continually fed into the computers. With a series of such reports, the formulas can then calculate what the weather is doing at a particular moment, assess how it is changing and forecast that change into the future.

Several important models are used in different countries, and the team studied their past successes and failures, calculating any biases.

For example, one model might consistently forecast too much or too little rain in an area while another might have trouble predicting the strength of wind coming from the north.

When they find problem areas they give less weight to that portion of the forecast from that particular computer, and if another is better on a particular area it gets more weight.

Combining the forecasts, allowing for the strengths and weaknesses of each, allows them to produce a single new forecast they call the “collective superensemble” that is better than the average of those involved, Krishnamurti explained.

“So it’s not just one model that it represents, it represents the best” of all of them, he said.

Zoltan Toth, who works on ensemble forecasting at the National Center for Environmental Prediction near Washington, said the report was very interesting.

“They look at all variables at all levels. I don’t think anyone has attempted to do this,” Toth said. “It’s primarily a bias remover,” he said, confirming that removing biases can reduce the error in the forecasts.

In his work on ensembles, Toth said, researchers use several computer models to produce a range of forecasts.

MODELS USED IN PROJECT

Eventually, Florida State scientists hope their model will be incorporated in standard weather forecasting but they are not really sure when that’s going to happen. Despite the success in its hurricane forecasting, the National Hurricane Center has yet to call for any data, said Williford.

In the meantime, these researchers will use the superensemble to test other key weather information such as global rainfall, shorter-term predictions such as one to six days, and longer-range predictions.

Among the computer forecast models being used in the Florida project are those from the Bureau of Meteorology Research Center and the Council of Industrial and Research Organizations, both in Melbourne, Australia; European Center for Medium Range Weather Forecasts, London; Geophysical Fluid Dynamics Laboratory, Princeton, N.J.; Japan Meteorological Agency, Tokyo; Laboratory Meteorologic Dynamique, Paris; Max Planck Institute, Hamburg, Germany; National Center for Environmental Prediction, Washington; Research Provision Numerique, Montreal and United Kingdom Meteorological Office, London.

from MSNBC’s Bobbi Nodell and the Associated Press

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