IR SATELLITE DATA ENABLES NEW APPROACH TO CYCLONE FORECASTING

Cyclones in the northern Indian Ocean are notoriously difficult to predict, due to incomplete atmospheric data in the region. After last year's Cyclone Nargis, one of the largest and most destructive cyclones on record, researchers from NASA reexamined the storm as a test case for a new data integration and mathematical modeling approach. Compiling satellite data from the days leading up to the 2 May landfall of the storm, the scientists hindcast Nargis's path and landfall in Burma using additional data and processing to better reveal the tropical cyclone's likely track.

"There is no event in nature that causes a greater loss of life than Northern Indian Ocean cyclones, so we have a strong motivation to improve advance warnings," says the study's lead author, Oreste Reale, an atmospheric modeler with the Goddard Earth Sciences and Technology Center.

Because they don't have access to hurricane hunters, forecasters from the India Meteorological Department and the U.S. Navy's Joint Typhoon Warning Center have to rely on remote satellite measurements that can only assess atmosphere and ocean temperatures under "clear sky," or cloudless, conditions, something that doesn't exist in the midst of a cyclone. Forecasting in this region is also difficult because large temperature contrasts between land and sea can lead to erratic storm tracks.

These difficulties led Reale and his team to look at modeling the cyclone in a new way. In their experiment, the researchers detected and tracked Nargis's path by employing novel three-dimensional satellite imagery and atmospheric profiles from the Atmospheric Infrared Sounder (AIRS) instrument aboard NASA's Aqua satellite to see into the heart of the storm.

AIRS has the ability to show changes in atmospheric temperature and moisture at varying altitudes. Until recently, many weather modelers were only using AIRS data from cloud-free skies. But in 2007, AIRS demonstrated the ability to obtain accurate atmospheric temperatures from "partly cloudy" data. Reale used the temperature data products to run the model with the added information from partially cloudy areas of sky that had not previously been included.

According to the scientists, agencies monitoring the region can access AIRS's data daily and optimize forecasts for cyclones in the Indian Ocean. The same technique could be useful to forecasts of hurricanes in the Atlantic and typhoons in the western Pacific, particularly when a storm has formed over the open ocean out of flight range of hurricane-hunting airplanes.

"With this approach, we can now better define cyclones at the early stages and track them in the models to know what populations may be most at risk," explains Reale. "And every 12 hours we gain in these forecasts means a gain in our chances to reduce loss of life."

Results from the study were published in a March issue of Geophysical Research Letters. (SOURCE: NASA)