Regional And Mesoscale Meteorology Team
Daily Satellite Discussion
Friday October 17, 1997
The coldest IR temperature is associated with the small overshooting cloud asssociated with the intense updraft. A V-shaped cold plume extends downstream from this point advected by the strong winds near the tropopause. A warmer "wake" also extends downstream such that each intense overshooting top can be quantified by the IR temperatures of a cold and a warm pixel (cold-warm couplet). Typically, cloud top temperatures are related to height due to the atmospheric lapse rates such that the higher the cloud the colder the IR temperature. With overshooting convective cloud tops the cloud top temperature relates to the parcel temperature which cools moist adiabatically as it rises. When one views cloud tops in visible imagery, the shading of the cloud tops can at times portray cloud height information. Stereo satellite and other techniques have been devised to compute such cloud top heights. With a severe thunderstorm some of the cloud which has advected downstream may actually appear warmer than some of the surrounding anvil cloud even though it is higher. This is due to the cloud remaining in the stratosphere above the tropopause inversion long enough to take on the temperature of that level. Therefore, the warm wake in IR imagery may often be due to stratospheric cloud, which has been produced by a very intense updraft.
The same pheneomena is seldom seen in the tropics, but has been observed, and takes on a different appearance due to cloud top winds being much weaker. This IR cloud top pattern will be the topic of an upcoming RAMM Satellite Discussion.