Scientists unlock Hurricane Lili's sudden death

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

Related stories:

Portable imaging system will help maximize public health response to natural disasters
Researchers at the Georgia Tech Research Institute (GTRI) have developed a low-cost, high-resolution imaging system that can be attached to a helicopter to create a complete and detailed picture of an area devastated by a hurricane or other natural disaster. The resulting visual information can be used to estimate the number of storm refugees and assess the need for health and humanitarian services.
Hurricane Ike tracked by ESA's Envisat
(PhysOrg.com) -- Residents along the Gulf Coast are bracing for Hurricane Ike as it travels over the Gulf of Mexico after ripping through Cuba and Haiti. ESA's Envisat satellite is tracking the storm, which is forecast to make landfall on the Texas coast by 13 September.
Key advance toward 'micro-spacecraft'
Fleets of inexpensive, pint-sized spacecraft are one giant leap closer to lift off. Researchers here at the 236th National Meeting of the American Chemical Society describe a new, razor thin temperature-regulating film that brings this sci-fi vision of "micro-spacecraft" weighing barely 50 pounds and 10-pound "nano-spacecraft" closer to reality.
2007 Hurricane Forecasts Took Blow from Winds and Saharan Dry, Dusty Air
(PhysOrg.com) -- A new analysis of environmental conditions over the Atlantic Ocean shows that hot, dry air associated with dust outbreaks from the Sahara desert was a likely contributor to the quieter-than-expected 2007 hurricane season.
NSF awards grant to track 'space weather' in Earth's near-space environment
Global and real-time "space weather" observations of near-Earth space--and the solar storms that can knock out electric power grids--is about to happen for the first time, thanks to funding from the National Science Foundation (NSF).
For Hurricanes, Storms, Raindrop Size Makes All the Difference
When Tropical Storm Gaston hit Richmond, Va., in August 2004, its notable abundance of small and mid-sized raindrops created torrential rains that led to unexpected flash flooding throughout the city and its suburbs. New research from NASA has concluded that tropical cyclones like Gaston produce rain differently than another class of storms called "extra-tropical" cyclones.
Scientists reveal presence of ocean current 'stripes'
An international collaborative of scientists led by Peter Niiler, a physical oceanographer at Scripps Institution of Oceanography, UC San Diego, and Nikolai Maximenko, a researcher at the International Pacific Research Center, University of Hawaii, has detected the presence of crisscrossing patterns of currents running throughout the world’s oceans. The new data could help scientists significantly improve high-resolution models that help them understand trends in climate and marine ecosystems.
2007 Hurricane Season Starts Early, Ends Late
The Atlantic Hurricane Season began early in 2007, and by mid-December it was still going. The season officially begins June 1 and ends Nov. 30. That means that for the most part, storms have formed and fizzled between those dates, or they used to.

News discussion:

Space & Earth science news