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A Hopeful Forecast: More Accurate Long

作者:admin 2020-09-27

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By the same token, there’s less readily available data to put into these models. The United States and other countries in the middle latitudes have hundreds of weather stations. But there are far fewer stations in the tropics because so much of that territory is covered by oceans. Also, many tropical countries lack the necessary funding to collect data via weather balloons, planes, drones and other costly devices.

Not being able to accurately predict the weather in the tropics, especially rain, has an outsized impact on the people who live there. Many make their living from farming, Dr. Judt said, and “it’s very difficult to plant crops and harvest when you don’t know when it will rain, how much it will rain and how long it will rain for.”

The tropics are also prone to extreme storms where “it just pours for hours and hours,” Dr. Judt said. Accurate weather predictions made farther in advance would better prepare communities and help prevent property damage, injuries and deaths resulting from flooding.

Dr. Judt’s findings, and those of scientists at Penn State and the University of Munich published in recent years, test the limits of a theory introduced in 1969 by Ed Lorenz, a prolific M.I.T. mathematician and meteorologist. He theorized that tiny disturbances in the atmosphere can build up and have vast impacts over time — a phenomena now known as the butterfly effect. This effect, he wrote, seems to ensure that predicting the weather more than two to three weeks ahead of time will always be mathematically impossible.

Scientists today call this roadblock the predictability horizon, a point of no return for weather forecasting. Anything beyond it is not much better than a random guess.

“Science has painted a fence around what it can do in a very spectacular way,” said Dr. Emanuel, who worked alongside Dr. Lorenz for more than three decades. No matter how much data you have or how powerful your computers are, he said, eventually your ability to improve “slows down and grinds to a halt.”

Still, things have improved over the past few decades, narrowing the gap between the aspirational and actual predictability of weather. Eugenia Kalnay, an atmospheric scientist at the University of Maryland in College Park who studies the predictability of weather, says the advent of weather satellites has revolutionized forecasting in the tropics.

“In the ’90s, we had almost no satellite observations in the southern hemisphere,” she said. “Since then, the number and quality of satellite observations has increased substantially,” so our ability to make accurate forecasts in the southern hemisphere is almost as good as in the northern hemisphere.

Additionally, the global weather models that are now in development can simulate showers and thunderstorms, Dr. Judt says, whereas existing models cannot. This, coupled with a series of weather satellites set to launch over the next few years, should translate to longer lead times for tropical forecasts.

“We should see an improvement in tropical weather prediction in the next 10 years,” he said.

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