Hawaii researchers hone storm technology
By Dan Nakaso
Advertiser Staff Writer
By Dan Nakaso
University of Hawai'i researchers used new technology to track the lives of Category 5 hurricanes Katrina and Rita like they'd never been able to track storms before — and they now hope to better forecast typhoons and hurricanes in the Pacific basin.
Old technology allowed researchers to measure lightning strikes in the eyewalls of hurricanes only in the final 12 hours or so of a hurricane's life — and only once it reached landfall, said UH meteorology professor Steven Businger.
But four new sensors stationed in Lihu'e, Kaua'i; Kona on the Big Island; Alaska; and Kwajelein Atoll that make up the new "PacNet sensor network" became the basis for Businger and former UH graduate student Kirt Squires to measure the entire life spans of hurricanes Katrina and Rita, from thousands of miles away — and even while the storms were still at sea.
The PacNet technology — and new methods of processing hurricane data — were applied to data and older sensors located along the southern coast of the United States to allow Businger and Squires to better measure lightning strikes in the eyewalls of Katrina and Rita.
"What we found went way beyond our expectations," Businger said. "They couldn't watch the whole history of these storms before. Now we can."
The study of lightning strikes inside Katrina and Rita by Businger and Squires will be published in an upcoming issue of the American Meteorological Society's Monthly Weather Review, tentatively scheduled for November.
"Hurricane forecasters and researchers are very interested in developing methods that allow a continuous examination of the structural growth of the eyewall within hurricanes. ... The relationship between the lightning activity and the storm's energy source means it's crucial for us to study and pick apart the evolution of the lightning," Squires said.
Their $308,000 research grant was split by NASA and the U.S. Office of Naval Research, which saw Hawai'i as an ideal location to measure thunderstorms over thousands of miles of open ocean.
"The study by Kirt and myself was focused on hurricanes," Businger said. "However, the technology has much broader applications to thunderstorms, squalls, kona lows, etc. Thunderstorms, in particular, are very important for airplanes and ships."
In August 2005, Katrina devastated much of the north-central Gulf Coast, with the most severe loss of life and property in New Orleans. Katrina was the sixth-strongest Atlantic hurricane ever recorded.
Just a month later, Rita made landfall in Louisiana near the Texas border and went on to cause extensive damage along the Louisiana and extreme southeastern Texas coasts. Rita was the fourth-most intense Atlantic hurricane ever recorded.
Using the reconfigured short-range lightning sensors, along with data collected from a NASA satellite and a National Oceanic and Atmospheric Administration P-3 "hurricane hunter" airplane, Businger and Squires specifically looked at the ferocity and frequency of lightning strikes in the eyewalls of Katrina and Rita that had never been measured before.
During the birth of both hurricanes, as they were rapidly building strength, Businger and Squires saw big spikes of lightning activity. Then, when the hurricanes were at their greatest intensity, more moderate lightning activity lasted over a longer period.
"This signature has never been seen before," Businger said as he reviewed the data in his office at UH last week. "It's new. What it means is we can see the whole life cycle of lightning in a storm versus just the last few hours."
More research needs to be done, Businger said, but the data could help meteorologists forecast the life spans — and intensity — of future Atlantic and Pacific tropical cyclones, the umbrella term for hurricanes and typhoons.
The key to the research was four long-range lightning sensors that can measure lightning strikes in hurricane eyewalls up to 4,000 miles away, compared to older sensors that can detect lightning strikes from only 100 miles away.
The new sensors use low-frequency bands, sort of like long AM-radio waves, compared to the older sensors that rely on frequencies that are more like short-band FM signals, Businger said.
The four new sensors are less accurate and can only measure lightning strikes within a "location accuracy" of about five kilometers versus their predecessors, which are accurate within 100 meters, Businger said.
"Everything's happening in the eyewall — storm surge, heavy rains, wind and lightning," Businger said.
FIFTH SENSOR COMING
Last month's Category 4 Hurricane Flossie, however, came into Hawai'i waters with little lightning. It could be the result of something specific to conditions around Hawai'i or perhaps the absence of a long-range sensor to the south of the Big Island, which would help collect more complete data, Businger said.
"We still don't understand enough why some hurricanes have a lot of lightning, while others have less," he said.
A fifth sensor is waiting to be installed, perhaps on Midway Atoll, which could provide better hurricane data for Hawai'i waters, Businger said. A new grant from the U.S. Office of Naval Research of more than $500,000 will fund seven new sensors by next August, he said, just in time for typhoon season.
Reach Dan Nakaso at email@example.com.