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INTERPRETATION DISCUSSION |
Regional and Mesoscale
Meteorology Team
Cooperative Institute for Research in the Atmosphere (CIRA)
Colorado State University Fort Collins, Colorado
November 20, 1998
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Today’s discussion focuses on the reflective properties
of ice cloud particles at 3.9 micrometers. Figure 1 is the 3.9 micrometer
image valid at 1930 UTC on Tuesday November 17, 1998. Figure 2 is
the 10.7 micrometer image at the same time. The minimum 10.7 brightness
temperature (Figure 2) at the center of the yellow circle is –62 C.
At the same location the minimum 3.9 micrometer brightness temperature
(yellow circle in Figure 1) is -3 C. The 59 C difference in brightness
temperature (Tb) between the channels is due to the increase in Tb by the
reflected component at 3.9 micrometers. The blue circle in western
CO encloses a cloud with a minimum Tb at 10.7 micrometers equal to –37
C, and a minimum Tb at 3.9 micrometers equal to –24 C. The cloud
in western CO has a 3.9 micrometer reflective component of 13 C, much less
than that of the cloud in eastern CO. This example shows that the
reflective component of ice clouds can vary dramatically, and that ice
clouds can be significantly reflective at 3.9 micrometers.
