Aided by new observations from the Coupled Boundary Layer Air-Sea Transfer (CBLAST) hurricane field program, scientists at the Rosenstiel School of Marine and Atmospheric Science have helped to develop and test a new, high-resolution computer model to better understand how air-sea interactions directly affect hurricane intensity, a factor not yet possible in the current operational forecast models.

The research, which is featured in the March 2007 issue of the Bulletin of the American Meteorological Society (BAMS), explains that current predictive models used in forecasting hurricane formation and intensity have difficulty accurately representing data such as ocean temperature, surface wind, rain and waves, and pressure and wind-speed relationships. A new fully coupled atmosphere-wave-ocean modeling system is capable of forecasting detailed hurricane inner-core structure, as well as surface temperature and wind, ocean currents, and surface waves that are crucial for improving hurricane intensity forecasts.

The CBLAST –Hurricane field program was conducted from 2002 to 2004 using NOAA’s “Hurricane Hunter” aircraft, as well as drifting buoys and subsurface floats deployed ahead of Hurricanes Fabian in 2003, and Frances in 2004. Dr. William Drennan, associate professor of applied marine physics and one of the scientists who participated in the fieldwork, has helped to provide an unprecedented amount of information about how variations in ocean and sea surface conditions can accelerate or inhibit the intensification of hurricanes.

“Measuring processes near the sea-surface in hurricanes is a challenge! The CBLAST field program which brought together many new ideas and techniques has provided a wealth of new data that will help us to improve our understanding of how hurricanes gain and lose energy,” Drennan said

Rosenstiel scientist Dr. Shuyi Chen, a professor of meteorology and physical oceanography, led CBLAST’s Hurricane modeling effort. She and other scientists have developed a fully coupled atmosphere-wave-ocean, high-resolution model able to predict the structure of a hurricane eye and eyewall at nearly a 1-km resolution, which is well within the recommendation for next-generation hurricane-prediction models set by the NOAA Science Advisory Board Hurricane Intensity Research Working Group.

“Extreme high winds, intense rainfall, large surface waves, strong ocean currents, and copious sea spray in hurricanes are all difficult to measure, limiting our capability in predicting their effects on hurricane intensity. The new coupled model takes into account the fully interactive nature of the atmosphere and ocean in tropical storms and represents an important first step toward developing the next-generation hurricane prediction models,” Chen said.

The effect of air-sea interactions on hurricane structure and intensity change is the main focus of the CBLAST-Hurricane program. The new, high-resolution model for hurricane research and prediction is a fully integrative modeling system, taking advantage of the new observations from the CBLAST field program to account for data from three important aspects of hurricane modeling. The overall modeling system is comprised of an atmospheric model, a surface wave model, and an ocean circulation model, all of which combine to form an innovative way of modeling storms.

CBLAST – Hurricane modeling and observation efforts were sponsored by the Office of Naval Research (ONR), and involved many scientists from numerous universities as well as from the National Oceanic and Atmospheric Administration (NOAA). "It is one of the most comprehensive studies ever of the way the ocean and atmosphere interact in hurricanes, offering the scientific community new pathways in modeling and observation that will lead to further predictive modeling progress. Improved weather forecasting will have global impacts; helping every nation affected by hurricanes and typhoons," said Dr. Linwood Vincent, Acting Head of the Ocean, Atmosphere and Space Research Division of ONR.

The 2005 Hurricane season highlighted the urgent need for better understanding of the factors that contribute to hurricane formation and intensity change, and for developing future predictive models to improve intensity forecasts. Scientists are hoping that with improved predictive science will come better preparation and warning for areas affected by tropical storms.

Source: University of Miami Rosenstiel School of Marine & Atmospheric Science.