Regional And Mesoscale Meteorology Team
Daily Satellite Discussion
Thursday October 23,1997
The water vapor image depicts the temperature of the optically thick layer of water vapor that is emmitting radiation at 6.7 micrometers. It is this radiation that the satellite detects. The temperature gives one an idea of the level of the optically thick layer of water vapor. A warmer temperature means that the water vapor is lower than a neighboring cooler region at a fixed time.
If the temperature of a region is cooling/warming that could imply that upward/downward vertical motion is occurring. Another reason could be that the cooler/warmer region simply advected in from somewhere else.
Compare the region about 20N and 140W in both figures. One can see that in time the region warmed significantly. Since the region of dark red in Figure 1 had expanded in time, this implies that sinking motion was responsible for the warming. If advection was the cause then the large dark red region in Figure 2 would have been seen in Figure 1 (at the same size), but at a slightly different location. As the region was much smaller in Figure 1 (and cooler) one must conclude that advection was not a significant factor.
Time changes in temperautre can imply vertical motion in the Lagrangian frame. If there is no temperature change then there is no vertical motion in this frame of reference.
Louie Grasso