Fog and Moisture Boundary Analysis from VIIRS

20130905_0717_sport_viirs_seus_ntmicro_fog_moist_vs_dry_example_annotated

A wide VIIRS swath covering parts of the Southeast U.S. provides a Night-time Microphysics RGB image showing wide fog in the valleys of Tennessee, Georgia, and North Carolina (see yellow outline in upper center of image).  Also of note is the difference in coloring between the areas above and below the white line stretching east-west from Mississippi to South Carolina.  The brighter purple coloring indicates drier air compared to the darker shades south of the line where the dewpoints were relatively high (in the +70F range).  In this case the red component of the RGB (12-11 micron difference), which is related to optical thickness, contributes less color in the areas of higher moisture; this results in a darker color of purple compared to the relatively drier air to the north.  The red decreases in the southern area because the difference in the 12-11 micron channels decreases from the values in the drier air.  Looking at the individual channels, this change is fairly small, on the order of 1-2 K; but the range of the channel difference for the red component is limited to 6 K total.  Hence a noticeable change in the red occurs and it brings out the change in air density.

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