| 3-D Hurricane Tracking - Science Insider
Reported September 2007
BACKGROUND: Forecasters are testing a new technique called VORTRAC -- Vortex Objective Radar Tracking and Circulation -- that provides a detailed 3-D view of an approaching hurricane every six minutes and allows them to determine whether the storm is gathering strength as it nears land. Then, they can quickly alert coastal communities if it suddenly strengthens.
HOW IT WORKS: Developed by researchers at the National Center for Atmospheric Research (NCAR), the technique relies on the existing network of Doppler radars along the southeast coast to closely monitor hurricane winds. Each radar can measure winds blowing toward or away from it, but no single radar could provide a 3-D picture of hurricane winds until now. The NCAR scientists developed a series of mathematical formulas, which combine data from a single radar near the center of a land falling storm with general knowledge of Atlantic hurricane structure in order to map the approaching system's winds in three dimensions. The technique also infers the barometric pressure in the eye of the hurricane, a very reliable index of its strength. However, because of the limited range of Doppler radars, VORTRAC works only for hurricanes within about 120 miles of land. In the future, it might be possible to use VORTRAC to help improve long-range hurricane forecasts by using data from airborne radars to glean detailed information about a hurricane far out to sea.
WHAT IS DOPPLER RADAR: Doppler radar uses a well-known effect of light called the Doppler shift. Just as a train whistle will sound higher as it approaches a platform and then become lower in pitch as it moves away, light emitted by a moving object is perceived to increase in frequency (a blue shift) if it is moving toward the observer; if the object is moving away from us, it will be shifted toward the red end of the spectrum. Doppler radar sends out radio waves, which bounce off objects in the air, such as raindrops or snow crystals, and then measures how much the frequency changes in returning radio waves to better determine wind direction and speed.
The American Geophysical Union and the American Meteorology Society contributed to the information contained in the TV portion of this report.
If you would like more information, please contact:
National Center for Atmospheric Research
Boulder, Colorado
(303) 497-1000
kconrad@ucar.edu
American Geophysical Union
Washington, DC 20009-1277
(800) 966-2481
http://www.agu.org
American Meteorological Society
Boston, MA 02108-3693
(617) 227-2425
http://www.ametsoc.org
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