Regional And Mesoscale Meteorology Team
Daily Satellite Discussion
Monday October 27,1997
Figure 1 shows the GOES-9 visible at 1745 UTC. In the image one can see large regions of "white". Some of this "white" is snow on the ground, high ice water clouds over snow, and low liquid water clouds over snow. The visible image is of little use in helping distinguish among them.
Figure 2 is the GOES-9 channel 2, 3.9 micrometers, at the same time as Figure 1. The first feature that one is "drawn" to is the bright region over eastern Nebraska and Kansas oriented north-south. This is a low-level liquid water cloud over both bare ground (in Kansas) and over snow covered ground (in Nebraska). Refer back to the visible to see how well channel 2 discriminates between snow and liquid water clouds during the day. The reason is due to the poor/high reflectivity of snow/liquid water cloud at this particular wavelength. Also of interest in this figure is the small but darker region over southeast Wyoming. There is little contrast between this feature and the surrounding area.
Figure 3 shows the GOES-9 channel 4, 10.7 micrometers, at the same time as the above two figures. The dark region referred to in Figure 2 over southeast Wyoming shows up well in this channel as an upper level ice water cloud (that is why it appears so dark in channel 2).
The above three figures clealy demonstrate the absolute need for multiple channel anaylsis in identifying ice water and liquid water clouds over snow covered ground.
Louie Grasso