Microwave Image
Rita was a category 5 hurricane with sustained winds of 150 mph and a
central pressure of 897 millibar at the time the data used to create these
AIRS images were retrieved. Storm position is approximately 470 southeast
of Galveston, Texas.
The image above shows how the storm looks through an AIRS Infrared window
channel. Window channels measure the temperature of the cloud tops or the
surface of the Earth in cloud-free regions. The lowest temperatures in
dark purple are associated with high, cold cloud tops that make up the top
of the hurricane. The infrared signal does not penetrate through clouds,
so the purple color indicates the cool cloud tops of the storm.
The infrared image reveals a very well developed eye at the center of the
storm. The red at the center of the eye indicates medium altitude clouds
are obscuring the eye, and the blue ring delineates the towering
thunderstorms of the eye wall ring. In cloud-free areas, the infrared
signal is retrieved at the Earth's surface, revealing warmer temperatures
except over open water (which appears colder due to lower emissivity).
Cooler areas are pushing to purple and warmer areas are pushing to red.
Green generally indicates the presence of clouds. Notice that some high
cold clouds as indicated in the infrared do not show up much in the
microwave. Microwaves are strongly affected by rain and ice crystals, so
some high clouds are almost certainly not raining and may be pretty thin
(like cirrus).
In the microwave image created from the AIRS microwave sensor (see figure
1), the large blue swath that previously extended into the Gulf is gone
(refer to AIRS Image Log). The big blue swath was a relatively clear area
ahead of Rita that was over the Gulf and the Atlantic. Now Rita has moved
closer to land and all the area over the ocean is taken up by the storm.
If there is clear air in front, it is over land and thus will show up hot
because of the emissivity of the land. Green generally indicates the
presence of clouds. The blue areas around the eye are indicative of very
high, cold cloud tops crowned by ice. These cloud towers are indicative of
strong convection and rain - these are strong high altitude thunderstorms
in the eye wall.
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.