Today's discussion looks at the use of the reflectivity product. The
reflectivity product has several advantages
because the reflectivity component of the 3.9 um IR imager channel is
emphasized.
The
loop
shows the fog product for Tuesday afternoon 19Z- 22Z. Notice
how well the fog in California shows up. The fog particles are more
reflective at cloud top because they are comprised of water droplets
which reflect more of the solar radaition at 3.9 than clouds composed
of ice crystals or snow. The weather observations have been plotted
on two images to show the extensive area of fog. Visibilities as low
as one-tenth of a mile were reported in the fog in the interior
valleys of California. Deadly car accidents have occurred in the
last 3 weeks due to dense fog. NOTE:The areas around the
northern Gulf of California in the Mexican Grand Desert exhibit
a "false fog" signal in this product due to differences in the
emissivity of the soils at 3.9 um and 10.7 um. For clarity,
red braces highlight a false fog area and yellow braces highlight a
real fog area.
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Average image
(click to enlarge)
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The loop was averaged to produce the average image shown above. Note
that the surface features appear very sharp where the skies have been
clear. In this case, much of the fog in the interior valley of
California shows up quite nicely as there were not any significant
clouds above the fog. You can also see fog in CO and UT. You can
even see the fog extending into northern california through the
cirrus cloud deck! Notice the areas that seem blurry. These areas
are where clouds were moving during the time period. The cirrus tends
to be the fastest moving cloud type and that is indicated in these
images. Also notice the low cloud area over the eastern Dakotas, this
cloud is less "blurred" as it was moving much slower than the high
cirrus clouds. However, the clouds off the west coast of California
do show a nice pattern indicating the low-level flow. The imagery is
less blurred because the cumulus that formed moved slower than the
cirrus. Finally, the last image shows the plotted (observed) visibility.
Note the low visibility of .1 reported in southern CA.
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Average image with surfac visibilities in miles.
(click to enlarge)
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Brian Motta
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