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NASA Satellite Catches a Hurricane Transforming Itself
01.30.06
 
Hurricanes can completely re-structure themselves inside, and that presents forecasters with great uncertainty when predicting their effects on the general population.

This is an image of Hurricane Ophelia (2005) from the Geostationary Operational Environmental Satellite (GOES) Image to right: This is an image of Hurricane Ophelia (2005) from the Geostationary Operational Environmental Satellite (GOES)-12 during the storm's warm-core tropical stages. Credit: Naval Research Laboratory, Marine Meteorology Division.

Recently, scientists used data from NASA’s Tropical Rainfall Measuring Mission (TRMM) satellite to analyze transformations that take place inside a hurricane. Stephen Guimond, a graduate research assistant at Florida State University, Tallahassee, Fla., lead a study that used TRMM data to view the height at which ice melts near the core of several tropical cyclones (the generic name for hurricanes or tropical storms), including Hurricane Ophelia in 2005.

“The temperature structure of a tropical cyclone is directly related to a storm’s wind speed and rainfall, which indirectly affects the storm surge,” Guimond said. It is important to monitor a storm’s thermal structure because this information assists meteorologists in estimating the impact on threatened areas of high winds, flash flooding and large storm surge.

This image, also from the GOES Image to left: This image, also from the GOES-12 satellite, shows Hurricane Ophelia (2005) interacting with a mid-latitude front draped across the northeastern U.S. as it loses some of it's tropical characteristics. Credit: Naval Research Laboratory, Marine Meteorology Division.

Many tropical cyclones transform into what are called “extra-tropical storms” as they move northward out of the tropics and into the mid-latitudes. During this stage, the storm’s cloud structure and high winds spread out over a wide area. As a result, the potential for heavy rainfall and large storm surge increases far from the center, potentially affecting life and property of more areas in the hurricane's path.

When Guimond and his colleagues at the Naval Research Laboratory in Monterey, Calif. looked at the data from TRMM’s Precipitation Radar instrument, they could see the temperature changes inside a tropical cyclone. One piece of information that gave researchers a clue that a storm was becoming extra-tropical was that ice particles, which are found high up in the cold regions of thick clouds surrounding the eye of the storm, melted at lower levels. Usually, when a tropical cyclone is still in the “tropical stages,” ice particles melt higher in the clouds.

TRMM satellite's Precipitation Radar instrument captured this view of Hurricane Ophelia on September 14, 2005. Image to right:The Tropical Rainfall Measuring Mission (TRMM) satellite's Precipitation Radar instrument captured this view of Hurricane Ophelia on September 14, 2005. This TRMM image was overlaid with visible imagery from the GOES-12 satellite to show more detail. The light yellow lines represent the path of the TRMM satellite's track and the light green below the storm's eye indicates the heaviest rainfall. Credit: Naval Research Laboratory, Marine Meteorology Division

By analyzing when and where ice particles are melting in tropical cyclones, researchers can better understand the various stages of an extra-tropical storm. This knowledge will help scientists re-create storms on computer forecast models, which can assist in the forecasting of future tropical cyclone transformations.

There is another benefit to using the data from NASA’s TRMM radar. Guimond said that the thermal or heat data inferred from the satellite reveals information on storm intensity and also gives clues about how a storm formed. This will help hurricane forecasters and researchers gain a better sense of how the tropical cyclone will develop in the future.

These findings were presented at the American Meteorological Society's 86th Annual Meeting in Atlanta.

This is a frame from the animation showing the coverage of the TRMM satellite during the life cycle of Typhoon Meari in 2004. Image to left: This animation (click on image to view animation - no audio - 4.5 Mb) shows the coverage of the TRMM satellite during the life cycle of Typhoon Meari (2004) in the western Pacific Ocean when the storm changed from tropical to extratropical. The outer yellow lines in the top image show the track of the TRMM Microwave Imager (TMI) instrument while the inner yellow lines show the track of the Precipitation Radar (PR). The thick black line in the top part of each image shows where the PR made a vertical slice through the storm. The side view associated with this slice is shown in the bottom part of each image and reveals how tall the clouds are inside the storm. The thin black line in the bottom part of each image is a 5 kilometers (3.1 miles) reference level with "A" and "Z" marking the beginning and end of the slice, respectively in both the top and bottom portions. In some of the later frames, the center of the storm is marked by a circle with a cross through the middle. In the beginning of the animation during Meari's tropical (warm-core) stages, the cloud tops are very high and clustered close to the storm center. However, as Meari enters the mid-latitudes and begins change into an extratropical storm (cold-core), the cloud tops are not quite as high and are moved away from the storm center. As a result, the large amounts of rainfall, high winds and storm surge expand and get shifted away from the storm center potentially affecting larger amounts of people. Credit: FSU

 
 
Rob Gutro
Goddard Space Flight Center