Figure 1
These false-color images show the amount of atmospheric water vapor observed by AIRS two weeks prior to the passage of Hurricane Isabel, and then when it was a Category 5 storm. The region shown includes parts of South America and the West Indies. Puerto Rico is the large island below the upper left corner.
Total water vapor represents the depth of a layer if all the water vapor
in the atmosphere were to condense and fall to the surface. The color bar
on the right sides of the plots give the thickness of this layer in
millimeters (mm). The first image, from August 28, shows typical tropical
water vapor amounts over the ocean: between roughly 25 and 50 mm, or 1 to
2 inches. The highest values of roughly 80 mm, seen as a red blob over
South America, corresponds to intense thunderstorms. Thunderstorms pull
in water vapor from surrounding regions and concentrate it, with much of
it then falling as rain.
Figure 1 shows total water during the passage of Hurricane Isabel
on September 13. The storm is apparent: the ring of moderate values
surrounding a very strong maximum of 100 mm. Total water of more than 80
mm is unusual, and these values correspond to the intense thunderstorms
contained within Isabel. The thunderstorms--and the large values of total
water--are fed by evaporation from the ocean in the hurricane's high
winds. The water vapor near the center of the storm does not remain there
long, since hurricane rain rates as high 50 mm (2 inches) per hour imply
rapid cycling of the water we observe. Away from the storm the amount of
total water vapor is rather low, associated with fair weather where air
that ascended near the storm's eye returns to earth, having dropped its
moisture as rain. Also seen in the second images are two small regions
of about 70 mm of total water over south America. These are yet more
thunderstorms, though likely much more benign than those in Isabel.
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.
