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Figure 1: July 19 Daylight Snapshot for PIA00438 | Figure 2: July 21 Daylight Snapshot for PIA00438 |
Hurricane Celia as observed by NASA's spaceborne Atmospheric Infrared
Sounder (AIRS). This image shows Celia on July 23 in visible light, as
you would perceive it from space. Located in the eastern north Pacific
Ocean off the coast of Mexico, Celia's winds have now dissipated to highs
of 40 mph. Celia was the first hurricane of the eastern north Pacific
season. Figure 1 is a daylight snapshot taken on July 19; Celia as
tropical storm, winds at 50mph. Figure 2 is a daylight snapshot taken on
July 21; Celia has a small eye with an 80-90% closed eyewall; sustained
winds at 75mph with gusts reaching 92mph; Celia is upgraded to hurricane
status.
The major contribution to radiation (infrared light) that AIRS channels
sense comes from different levels in the atmosphere, depending upon the
channel wavelength. To create the movies, a set of AIRS channels were
selected which probe the atmosphere at progressively deeper levels. If
there were no clouds, the color in each frame would be nearly uniform
until the Earth's surface is encountered. The tropospheric air temperature
warms at a rate of 6 K (about 11 F) for each kilometer of descent toward
the surface. Thus the colors would gradually change from cold to warm as
the movie progresses.
Clouds block the infrared radiation. Thus wherever there are clouds we can
penetrate no deeper in infrared. The color remains fixed as the movie
progresses, for that area of the image is "stuck" to the cloud top
temperature. The coldest temperatures around 220 K (about -65 F) come
from altitudes of about 10 miles.
We therefore see in a 'surface channel' at the end of the movie, signals
from clouds as cold as 220 K and from Earth's surface at 310 K (about 100
F). The very coldest clouds are seen in deep convection thunderstorms over
land.
Movies
Quick Time Movie July 20
Quick Time Movie July 22 Celia located in upper left. The other intense
convection area towards the center of the granule exhibits no circulation.
Quick Time Movie July 23 Dry air is now eating into Celia; the storm is
becoming disorganized and weak.
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.