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Figure 1: Microwave 89Ghz image | Figure 2: Visible/near infrared sensor |
Hurricane Ivan is the most powerful hurricane to hit the Caribbean in 10
years. On September 7 and 8 it damaged 90 percent of the homes in Grenada
and killed at least 16 people as it swept over Grenada, Barbados and the
other islands in the area. By Thursday morning on September 9, Ivan's
sustained winds reached 160 mph making it a rare category 5 hurricane on
the Saffir-Simpson scale. By Monday September 13, Ivan is blamed for 67
deaths and skirts western Cuba with winds clocked at 156 mph. The National
Hurricane Center predicted the eye of Ivan will make landfall across
Mobile Bay in Alabama late Wednesday or early Thursday.
These images of Hurricane Ivan were acquired by the AIRS infrared,
microwave, and visible sensors on September 15 at 1:30 pm local time as
the storm moves in to Alabama. Ivan at category 4 strength is about 150
miles south of Mobile, Alabama and is moving north at 14 mph. Maximum
sustained winds are reported to be at 135 mph and extend 105 miles from
the center, while tropical storm-force winds extend 290 miles from the
center. Ivan pounded the Gulf coast all day Wednesday, and is expected to
make landfall between midnight and 3am in Mobile Bay, Alabama.
This image shows how the storm looks through an AIRS Infrared window
channel, and reveals a very large eye - about 75 km (50 miles) across.
Window channels measure the temperature of the cloud tops or the surface
of the Earth in cloud-free regions. The lowest temperatures 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. In cloud-free areas, the
infrared signal is retrieved at the Earth's surface, revealing warmer
temperatures. Cooler areas are pushing to purple and warmer areas are
pushing to red.
The microwave image (figure 2) reveals where the heaviest precipitation
in Ivan is taking place. The blue areas within the storm show the location
of this heavy precipitation. Blue areas outside of the storm where there
are moderate or no clouds are where the cold (in the microwave sense) sea
surface shines through. The image shows that the largest area of intense
convection/precipitation is in the NE quadrant, centered near New Orleans.
There is a smaller but still quite intense area in the SE quadrant
trailing the center of the storm that might impact the Alabama coast.
Image Journal
September 7, Tuesday, 1:30 am. - infrared, 12micron
The infrared signal does not penetrate through clouds, so the purple color
reveals the cool cloud tops of the hurricane. In cloud-free areas, the
infrared signal is retrieved at the Earth's surface, revealing warmer
temperatures. Ivan becomes better organized as it approaches the Windward
Islands. The center of the storm is 170 miles (275 km) southeast of
Barbados and moving west at 21 mph (33 km/hr). Maximum sustained winds
near 105 mph which extend outward at this force for 70 miles (110 km).
September 7, Tuesday, 1:30 am. - microwave, 89GHz
September 8, Wednesday, 1:30 am. - infrared, 12micron
The infrared signal does not penetrate through clouds, so the purple color
reveals the cool cloud tops of the hurricane. In cloud-free areas, the
infrared signal is retrieved at the Earth's surface, revealing warmer
temperatures. Ivan becomes better organized as it approaches the Windward
Islands. The center of the storm is 170 miles (275 km) southeast of
Barbados and moving west at 21 mph (33 km/hr). Maximum sustained winds
near 105 mph which extend outward at this force for 70 miles (110 km).
September 8, Wednesday, 1:30 am. - microwave, 89GHz
September 10, Friday, 1:30 pm. - infrared, 12micron
Ivan closes in on Jamaica. With only 85 miles between the storm and the
island, Ivan's winds at category 4 are sustained at 145 mph (230 km/hr).
Hurricane-strength winds extend up to 60 miles from the center of Ivan,
and tropical-storm force winds are up to 175 miles from the center. Ivan
is now better organized and has a well-defined eye. After Ivan leaves
Jamaica, it is expected to hit western Cuba, probably making landfall
later Sunday as a CAT 4 hurricane.
September 10, Friday, 1:30 pm. - microwave, 89GHz
September 10, Friday, 1:30 pm. - visible/near-infrared
September 13, Friday, 1:30 pm. - infrared, 12micron
Ivan's winds at category 5 strength are sustained at 160 mph (260 km/hr)
and extend out to 105 miles from the center. Tropical-storm force winds
are up to 205 miles from the center. The infrared image shows that the
eye has grown quite large - perhaps 40 km (25 miles) across - which is
sometimes an indication of weakening but may not be in this case. The
surface pressure at the time of this image was estimated by the National
Hurricane Center at 915 mb and falling - consistent with a very intense
and strengthening hurricane.
September 13, Friday, 1:30 pm. - microwave, 89GHz
The microwave image
shows that Ivan has again developed two distinct convective centers,
separated by about 250 km. That pattern developed on September 5 and
persisted for 4 days. It disappeared while the storm was passing over
Jamaica, but it has now re-formed.
September 13, Friday, 1:30 pm. - visible/near-infrared
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.