Today's discussion looks to the north in the GOES imagery. The remapped 10.7 um image shown below (left) is
from GOES-8. The surface temperatures are so cold in the northern portions of the provinces of Ontario, Manitoba,
and Saskatchewan that they appear colder than the clouds. This is typically not the case in the US.
When noticing this in the
animation,
you can actually see warmer clouds passing over the very cold ground.
Also notice the diurnal temperature changes along the coast of Hudson Bay. The temperatures cool rapidly
during the night where the skies are clear because the earth's longwave radiation escapes to space and creates
a positive feedback process until sunrise. Also notice the sharp contrast between Hudson Bay and the
nearby land/snow-surface temperatures.
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Figure 1
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Figure 2
click to enlarge |
A comparison of the remapped 10.7 um IR image with the remapped GOES-8 and GOES-9 composite 6.7 um (water vapor) image (right)
reveals that even in the coldest and probably driest (in the absolute sense) air masses, the water vapor channel does not indicate direct
sensing of the surface. The clouds are easier to discern in the 6.7 um image because the cold surface background is not seen and the
warmer brightness temperatures associated with the water vapor offer a better contrast with the colder cloud areas.
Finally, below is the 1215 UTC image with the surface temperatures overlayed on the 10.7 um IR image. Where the skies are clear,
notice how similar the surface temperatures and brightness temperatures are. For instance, the -37 C on the west coast of Hudson
Bay compares with -39 C brightness temperature. Similar comparisons were done for the area north of the approaching cloud
system and to the south of Hudson Bay and were found to be within 4 degrees C.
Brian Motta
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Figure 3
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