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| Figure 1: AIRS channel 2333 (2616 cm-1) | Figure 2: HSB channel 2 (150 GHz) |
Three different Views of Hurricane Isidore from the Atmospheric Infrared
Sounding System (AIRS) on Aqua.
At the time Aqua passed over Isidore, it was classified as a Category 3
(possibly 4) hurricane, with minimum pressure of 934 mbar, maximum
sustained wind speeds of 110 knots (gusting to 135) and an eye diameter
of 20 nautical miles. Isidore was later downgraded to a Tropical Storm
before gathering strength again.
This is a visible/near-infrared image, made with the AIRS instrument. Its
2 km resolution shows fine details of the cloud structure, and can be
used to help interpret the other images. For example, some relatively
cloud-free regions in the eye of the hurricane can be distinguished. This
image was made with wavelengths slightly different than those seen by the
human eye, causing plants to appear very red.
Figure 1 shows high and cold clouds in blue. Figure 2 shows heavy rain
cells over Alabama in blue. This image shows the swirling clouds in white
and the water of the Gulf of Mexico in blue. The eye of the hurricane is
apparent in all three images.
Figure 1 shows how the hurricane looks through an AIRS Infrared window
channel. Window channels measure the temperature of the cloud tops or
the surface of the Earth in clear regions. The lowest temperatures are over
Alabama and are associated with high, cold cloud tops at the end of the
cloud band streaming from the hurricane. Although the eye is visible, it does
not appear to be completely cloud free.
Figure 2 shows the hurricane as seen through a microwave channel of the
Humidity Sounder for Brazil (HSB). This channel is sensitive to humidity,
clouds and rain. Unlike the AIRS infrared channel, it can penetrate
through cloud layers and therefore reveals some of the internal structure
of the hurricane. In this image, the green and yellow colors indicate
clouds and heavy moisture, while blue indicates scattering by
precipitation in intense convection. Orange indicates warm, moist air
near the surface. The ocean surface, could it be seen, would appear
slightly colder (yellow to green) due to the relatively low emissivity
of water. Three sets of eye walls are apparent, and a number of intense
convective cells can also be distinguished.
In the near future, weather data derived from these images will allow us
to improve our forecasts and track the paths of hurricanes more
accurately. The AIRS sounding system provides 2400 such images, or
channels, continuously.
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.
