Scientists unlock Hurricane Lili's sudden death

Jan 30, 2006
Hurricane Lili
Hurricane Lili was a Category 1 hurricane, and was centered over Louisiana on Oct. 3, 2002. This image was taken by the Moderate Imaging Spectroradiometer (MODIS) instrument, aboard NASA's Terra satellite. At this time, Lili had sustained winds of 92 mph near the center. On October 4, Lili was absorbed by an extratropical low while moving northeastward near the Tennessee/Arkansas border.

Using a fleet of NASA and other satellites as well as aircraft and other observations, scientists were able to unlock the secret of Hurricane Lili's unexpected, rapid weakening as she churned toward a Louisiana landfall in 2002. The data from multiple satellites enabled researchers to see dry air move into the storm's low levels, partially explaining why Lili weakened rapidly.

This study focuses on the rapid weakening of Hurricane Lili over the Gulf of Mexico beginning early on Oct. 3, 2002. During this time span, Hurricane Lili rapidly weakened from a category 4 to a category 1 storm, with its maximum sustained winds decreasing by 45 knots (51.8 mph) in the 13-hour period, until she made landfall in Louisiana. Operational computer models failed to predict this rapid weakening, which is not well-understood.

The study is being presented at the 86th Annual Meeting of the American Meteorological Society in Atlanta, Ga., during the week of Jan. 30. It was conducted by researchers from Mississippi State University (MSU), Mississippi State, Miss., and the National Center for Atmospheric Research (NCAR), Boulder, Colo.

"Because a polar-orbiting satellite can only obtain regional observations once per day, the ability to combine observations from multiple satellites over the data-sparse ocean is a key to understanding tropical cyclone intensity change," says Dr. Pat Fitzpatrick, the principal investigator from MSU.

In order to dissect this complex puzzle, scientists turned to data from NASA's Terra, Aqua, QuikSCAT and Tropical Rainfall Measuring Mission (TRMM) satellites, as well as data from the National Oceanic and Atmospheric Administration's Advanced Very High Resolution Radiometer (AVHRR) aboard Geostationary Operational Environmental Satellite (GOES). They also looked at data from sensors called "dropsondes" that were dropped from hurricane hunter airplanes while flying over Hurricane Lili. Those dropsondes provided temperature, humidity and wind data.

The different satellites provided a variety of data to look at the hurricane's components. QuikSCAT provided surface winds; Aqua provided high-resolution temperature and moisture profile data; and GOES-8 supplied upper-level winds. Sea Surface Temperature data was also measured from Aqua, Terra, TRMM and AVHRR. Standard weather observations were also incorporated, including maritime surface data from the National Data Buoy Center.

All of these different components were fed into an NCAR computer model called MM5 that re-creates atmospheric and oceanic conditions in four dimensions (height, width, area and time). The data was combined using a "Four-Dimensional Variational Analysis" (4DVAR) system. The MM5 computer model and 4DVAR system, developed by NCAR scientists, essentially re-created the conditions when Hurricane Lili weakened, so scientists could better understand the cause of the drop in strength. The model showed that low-level drier air, not observed in the conventional data, moved into the west side of Lili, at 00 Universal Time on Thursday, Oct. 3, 2002, (Wednesday, Oct. 2, at 8:00 p.m. ET), partially explaining the storm's weakening.

That dry air created an "open eyewall" which is basically a break up in the powerful thunderstorms that circle the open air center (eye) of the hurricane. Once the eyewall starts to break down, the storm weakens quickly.

The computer model also showed that the GOES upper-level wind data and QuikSCAT satellite wind information can improve hurricane track forecasts. "These satellites, through the 4DVAR technique, improved the inner-core wind structure and also defined the steering currents better," Fitzpatrick said. When this additional wind data from those two satellites was input, the computer model was also able to better re-create Hurricane Lili's track at landfall.

A paper on this subject has been submitted for review to Monthly Weather Review on the 4DVAR experiments, titled "The Impact of Multi-satellite Data on the Initialization and Simulation of Hurricane Lili's (2002) Rapid Weakening Phase." The scientists involved in this project are Xiaoyan Zhang and Qingnong Xiao, of the NCAR; and Pat Fitzpatrick, Nam Tran, Yee Lau, and Sachin Bhates of MSU.

Source: NASA

Explore further: Computer model shows moon's core surrounded by liquid and it's caused by Earth's gravity

add to favorites email to friend print save as pdf

Related Stories

Ex-Qualcomm exec pleads guilty to insider trading

6 hours ago

A former high-ranking executive of US computer chip giant Qualcomm pleaded guilty Monday to insider trading charges, including trades on a 2011 deal for Atheros Communications, officials said.

Media venture creates press litigation fund

7 hours ago

The media venture created by entrepreneur Pierre Omidyar said Monday it was establishing a fund to help defend journalists in cases involving freedom of the press.

'Moral victories' might spare you from losing again

7 hours ago

It's human nature to hate losing. Unfortunately, it's also human nature to overreact to a loss, potentially abandoning a solid strategy and thus increasing your chances of losing the next time around.

Recommended for you

Comet Jacques makes a 'questionable' appearance

4 hours ago

What an awesome photo! Italian amateur astronomer Rolando Ligustri nailed it earlier today using a remote telescope in New Mexico and wide-field 4-inch (106 mm) refractor. Currently the brightest comet in ...

Image: Our flocculent neighbour, the spiral galaxy M33

4 hours ago

The spiral galaxy M33, also known as the Triangulum Galaxy, is one of our closest cosmic neighbours, just three million light-years away. Home to some forty billion stars, it is the third largest in the ...

Titan offers clues to atmospheres of hazy planets

4 hours ago

When hazy planets pass across the face of their star, a curious thing happens. Astronomers are not able to see any changes in the range of light coming from the star and planet system.

Having fun with the equation of time

4 hours ago

If you're like us, you might've looked at a globe of the Earth in elementary school long before the days of Google Earth and wondered just what that strange looking figure eight thing on its side was.

User comments : 0