Regional And Mesoscale Meteorology Team
Daily Satellite Discussion
Monday November 3,1997
It is not only liquid water clouds which have this relationship between the emissivities at 3.9 and 10.7 micrometers. Certain soil types will also have an emissivity at 3.9 micronmeters that is significantly less than at 10.7 micrometers. Such areas will also have the white liquid water cloud signal, but will be free from fog/stratus. An example of this is the northern shore of the Gulf of California (red arrow). The similarity in appearance to fog/stratus can be seen by comparing this area with cloud/fog covered areas, those pointed to by the yellow arrows in the fog product image (Figure 1). Figure 2 is a visible image taken shortly after sunrise, with arrows marking the same features as the fog product. This image shows a greater difference between the appearance of the fog/stratus areas and the northern shore of the Gulf of California. But even at visible wavelengths the difference is not great. A look at the two accompanying loops assists in the distinction, in that the cloudy areas show movement, and the Gulf of California northern shore does not. Furthermore, the shore's "false fog" signal can be seen on every night, as long as the region is not obscured.
So keep an eye out for other "false fog" signals.
fog product loop
visible loop
Jack Dostalek