NASA Aircraft Captures Windy Details in Hurricane's Ups and Downs
Hurricanes not only threaten lives and property, they also often behave erratically, with seemingly endless shifts in intensity and movement that have long challenged forecasters. But new research using sophisticated weather research tools is shedding new light on the nature of these fickle storms.
Image right: This image from the Moderate Resolution Imaging Spectroradiometer on NASA’s Terra satellite shows Hurricane Dennis in the Gulf of Mexico on July 10, 2005. At the time, Dennis was a category 4 hurricane, with maximum sustained winds of 135 miles per hour. Credit: NASA/GSFC
Flying over Hurricane Dennis in July 2005 - a category 4 hurricane - with NASA's ER-2 aircraft and the National Oceanic and Atmospheric Administration's (NOAA) P-3 aircraft, scientists took measurements of the storm's internal structure. The information is giving clues about the evolution of a hurricane's warm inner core and the factors related to its formation.
Joe Turk, Steve Miller, and Jeff Hawkins of the Naval Research Laboratory, Monterey, Calif., and Steve Guimond of Florida State University, Tallahassee, Fla., will present their findings today at the American Geophysical Union's 2006 Fall Meeting in San Francisco.
The research flights were conducted as part of the Tropical Cloud Systems and Processes (TCSP) mission in Costa Rica, a NASA field experiment with cooperative participation from NOAA and several universities. This experiment was aimed at studying the birthing conditions for tropical storms and hurricanes and identifying the factors that cause them to strengthen or weaken.
"This campaign was particularly unique because two types of aircraft provided measurements on different atmospheric variables," said Turk. "The information is also being used to determine how accurately satellites capture storm details." While a few satellites can now look through clouds, the aircraft data provide a level of detail far superior to satellites.
Image left: A vertical slice through the center of Hurricane Dennis shows the rainfall structure across the entire storm, as measured by NASA's ER-2 Doppler radar on July 9, 2005. Warm colors indicate the presence of heavy rainfall and ice within the storm while cool colors show lighter rain. The feature at about 110 kilometers (68 miles) is an intense cloud called a "hot tower" with strong winds throughout the core. The approximate location of the eye is marked by slanted black lines.
Credit: Florida State University
Dennis reached hurricane strength on July 7, 2005, in the eastern Caribbean Sea, and rapidly strengthened into a category 4 storm before making landfall in Cuba on July 8. After weakening over land, Dennis quickly re-intensified over the Gulf of Mexico before weakening again prior to its second landfall in Florida.
As the storm fluctuated in intensity, flights into the storm continued, taking critical measurements of wind, rainfall, temperature, and moisture. "The erratic nature of the storm and the timing of the research mission allowed scientists to pierce through the core of the hurricane at many stages of its life cycle and for the first time map a hurricane's entire evolution," said Guimond.
Image right: NOAA's P-3 research aircraft. Click image to enlarge. Credit: NOAA
NASA's ER-2 Doppler radar measured wind speed along the track of the aircraft including measurements indicative of the size and concentration of raindrops and ice particles, while another ER-2 instrument, the Advanced Microwave Precipitation Radiometer, gathered microwave imagery of the internal structure of rain clouds. By analyzing when and where strong winds are occurring, researchers can better determine when intensity changes may occur. Data on the storm's vertical temperature structure - indirectly related to wind speed and rainfall - was also examined from overpasses of NOAA satellites.
Previous research has suggested that rapid hurricane intensification, like that seen in Dennis, is linked to hot towers, rain clouds that reach at least the top of troposphere - the lowest layer of the atmosphere - and about nine miles high in the tropics. They are called "hot" because of the large amount of latent heat they release, fuel for strong winds and heavy rainfall.
"With Dennis, it appears the hot towers played a major role in the rapid intensification of the storm, giving clues on how energy is concentrated and winds evolve at various stages of development," said Guimond. "The observations also helped place the storm's behavior in greater context and matched well with computer model simulations, suggesting that we are making progress in replicating hurricane development."
Image left: NASA's ER-2 research aircraft. Credit: NASA/JPL
While meteorologists have made considerable strides in forecasting a hurricane's track, intensity predictions have remained a more significant challenge. Part of the difficulty is that the many factors that control intensity, particularly the speed, direction and spin of air throughout the atmosphere, are constantly changing and difficult to measure.
+ NASA ER-2 research aircraft
+ NOAA P-3 feature
+ Hot Towers feature
Goddard Space Flight Center