In a new NASA-funded study, researchers have dramatically improved the warning time for tropical cyclone development in the Atlantic and Eastern Pacific hurricane basins. Using satellite data to access a combination of the spin of the atmosphere and wind speed data, researchers were able to detect potential tropical cyclones more than 40 hours earlier than with traditional methods, giving more time for warnings and preparation.
Researchers from Florida State University's Center for Ocean-Atmospheric Prediction Studies used data from the Quick Scatterometer, a satellite managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif., and the Seawinds instrument, built by JPL. The researchers detected the formation of systems that might become tropical cyclones prior to their being classified as tropical depressions by the National Hurricane Center. This new method is based on signals from the scatterometer-derived vorticity field, which highlights areas of rotating winds.
Tropical cyclones are also known as tropical depressions, tropical storms or hurricanes, depending on their wind speed. The National Hurricane Center uses criteria other than vorticity, such as persistent and organized thunderstorm activity, before it classifies a system as a tropical cyclone. In this study researchers used only the wind field data that is often present prior to the other criteria. Early detection of these systems will help determine those that warrant further examination by more traditional methods, and allow investigators to study the genesis of tropical cyclones by watching the full development of a storm from its very beginning.
"Earlier detection of potential tropical cyclones would give the public and maritime interests more time to prepare for a potential future threat," stated Ryan Sharp, co-author of the study and a researcher at Florida State University's Center for Ocean-Atmospheric Prediction Studies. "Advanced detection will also allow scientists more time to plan research missions into storms."
The objective technique used by the researchers to detect tropical cyclones was established by using data collected during the 1999 Atlantic hurricane season. This technique was then applied to the near-real-time (less than 3-hour delay) data for the 2001 Atlantic and Eastern Pacific hurricane seasons to detect systems that had the potential to become tropical cyclones.
Of the 17 tropical cyclones that developed in the Atlantic in 2001, eight were detected an average of 43 hours before they were classified by the National Hurricane Center. Some of the systems detected by this method (35 to 40 percent) never developed into tropical cyclones, but by using conventional methods of detection such as clouds in satellite pictures, researchers could eliminate most of these "false alarms" early in the study.
The results obtained by using the scatterometer in the Eastern Pacific, however, are more impressive and critical. With fewer weather stations and search aircraft, the use of the scatterometer can greatly improve tropical cyclone identification and prediction. Using the technique in this study, of the 17 tropical cyclones that formed in the Eastern Pacific, 14 were identified an average of 42 hours before they were classified as tropical cyclones by the National Hurricane Center. For a system developing close to land, this earlier prediction could mean the difference between life and death for those living in the region.
The Seawinds instrument is a specialized microwave radar that measures the speed and direction of winds near the ocean surface. Launched June 19, 1999, from California's Vandenberg Air Force Base, it operates in a Sun-synchronous, 803-kilometer (497-mile) near-polar orbit, circling Earth every 100 minutes, taking approximately 400,000 measurements over 90 percent of Earth's surface each day.
JPL manages the Quick Scatterometer satellite for NASA's Office of Earth Science, Washington, D.C. JPL also built the Seawinds scatterometer instrument and provides ground science processing systems. NASA's Goddard Space Flight Center, Greenbelt, Md., managed development of the satellite, designed and built by Ball Aerospace & Technology Corp., Boulder, Colo. NASA's Earth Science Enterprise is a long-term research and technology program designed to examine Earth's land, oceans, atmosphere, ice and life as a total integrated system.
The Office of Naval Research, Secretary of the Navy Grant to Dr. James J. O'Brien at Florida State University, provided additional funding for this study.
JPL is a division of the California Institute of Technology in Pasadena.