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Vis/NIR image close-up | AIRS infrared window channel | HSB microwave channel |
Three Different Views of Supertyphoon Pongsona, December 2002
Packing gusts of 296.1 kilometers per hour (184 miles per hour) and
sustained winds of 241.4 kilometers per hour (150 miles per hour),
Supertyphoon Pongsona struck the U.S. Island of Guam on Sunday, December
8. The storm cut off electricity over the entire island along with
telephone and water service, and President George W. Bush declared the
U.S. territory a federal disaster area. Pongsona is the third typhoon to
hit Guam since June, and the second cyclone of supertyphoon status to hit
in five years.
These images were made from data acquired by the Atmospheric Infrared
Sounding System (AIRS) instrument suite aboard NASA's Aqua spacecraft
just as the eye of the storm was about to pass over Guam.
This image was made using visible/near-infrared data using the AIRS
instrument. Its 2-kilometer (1.24-mile) resolution shows fine details of
the cloud structure and can be used to help interpret the other images.
It confirms that the eye was not cloud free at the time the data was
acquired, and pinpoints towering thunderheads rising up in several areas
of the spiral arms (see figure 1 for close-up).
The image in figure 2 shows how the typhoon looks through an AIRS
infrared "window" channel, which measures the temperature of the nearest
impenetrable surface. Where the sky is clear, this window channel shows
the surface of the Earth, otherwise it will show cloud tops. High cold
clouds appear blue, while lower warmer clouds are green through orange.
The Earth's surface, where it can be seen between the clouds, is warmest
and appears red. Although the storm has a clearly defined eye, it is not
cloud free and therefore shows up as yellow in this infrared image.
The image in figure 3 shows how the typhoon looks through a microwave
channel of the Humidity Sounder for Brazil (HSB), a component of the AIRS
instrument suite. This channel, which is sensitive to humidity, clouds
and rain, sees through much of the clouds and reveals some of the inner
structure of the storm. Here the eye is more clearly defined than in the
infrared image and appears to be very large - perhaps 80.5 kilometers (50
miles) across. Rain areas appear as blue patches, and a very intense rain
cell can be seen right over Guam itself. This cell is in the leading eye
wall and is probably associated with the highest wind speeds. It is likely
that much of the damage in Guam was caused by this particular part of the
storm.
In the near future, when estimates of the three-dimensional distribution
of the temperature, humidity and clouds in the atmosphere are also
routinely derived from the AIRS sounding system, it will be possible to
get a unique view of the interior of destructive storms like Pongsona.
The new knowledge gained will eventually make for more accurate forecasts
of such events.
The Atmospheric Infrared Sounder Experiment, with its visible, infrared,
and microwave detectors, provides a three-dimensional look at Earth's
weather. Working in tandem, the three instruments can make simultaneous
observations all the way down to the Earth's surface, even in the
presence of heavy clouds. With more than 2,000 channels sensing different
regions of the atmosphere, the system creates a global, 3-D map of
atmospheric temperature and humidity and provides information on clouds,
greenhouse gases, and many other atmospheric phenomena. The AIRS Infrared
Sounder Experiment flies onboard NASA's Aqua spacecraft and is managed by
NASA's Jet Propulsion Laboratory, Pasadena, Calif., under contract to
NASA. JPL is a division of the California Institute of Technology in
Pasadena