Scientist delves into quirks of Big Isle weather

Optical turbulence, frozen precipitation and strong subtropical highs — all playthings of the scientists who forecast what’s going on in the sky above Hawaii Island.

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Optical turbulence, frozen precipitation and strong subtropical highs — all playthings of the scientists who forecast what’s going on in the sky above Hawaii Island.

The public learned about the interaction of weather, high-altitude forecasting and astronomy Friday from an expert who helped found the Mauna Kea Weather Center. About 350 people who packed the Kahilu Theatre in Waimea also heard about the future impacts of global warming on the islands and learned the nuts and bolts of Hawaii’s unique and often fascinating weather.

University of Hawaii atmospheric science professor Steven Businger, with 30 years of research on destructive storms, told the audience how he had to shift his focus when it became obvious in the 1990s that the community of astronomers clustered on the summit required forecasting tailored to their specifications.

“The astronomers didn’t care about storms,” Businger said. “They wanted to know about good weather and how good it’s going to be.”

Astronomers also wanted to pinpoint predictions on the summit’s nighttime temperatures so they could precisely match them to the temperatures of the optical mirrors within the telescopes. If the lens was warmer than the night air, heat dispersing from the mirrors would distort images, Businger said.

Formed in 1998, the weather center today issues forecasts for telescope mirror temperatures that are accurate to within a degree. It also predicts telescope windshake, water vapor and optical turbulence, among other factors.

It’s all designed to help astronomers know as much as they can about how clearly they will be able to peer into space.

Turbulence will cause light distortions that have to be corrected by a method known as adaptive optics, said Randy Campbell, support astronomer for Keck. Cloud cover and high humidity also will hamper observations, making the work of the weather center invaluable, Campbell said outside the theater.

The talk was presented by W.M. Keck Observatory, which is headquartered in Waimea.

How will global warming impact Hawaii? The islands’ station in the moisture-rich tropics is a double-edged sword, Businger said.

“Yes, we’ll be buffered, and the temperature will rise more slowly, but our ecosystem is very finely tuned to a much smaller temperature range,” Businger said.

Thinner cloud layers mauka could upset balances in the rainforests, Businger said, and the number of hurricanes also will increase slightly, according to climate models.

“Our climate is going to be warmer than it’s ever been by 2036,” he said.

Businger also presented recent science on how vog causes a sharp increase in lightning activity.

“With Tropical Storm Flossie, lightning fired up like crazy when we got vog into the storm,” he said. “It caused the convection to be more intense.”

Tropical Storm Iselle, which inhaled a good dose of vog, also packed a lot of lightning. Hurricane Julio passed just to the north and didn’t have much lightning, Businger said. The vog particulates allow water to condense in smaller amounts, allowing them to be blown higher into the zone where the interaction with freezing temperatures creates the lightning, he said.

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These days, Businger is developing the science of long-range lightning detection using sensors. He also is working on smoke dispersion and vog modeling that could one day benefit Puna residents who deal with air sullied by off-gassing lava and smoke from the vegetation it burns.

Email Bret Yager at byager@westhawaiitoday.com.

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