NOAA-NESDIS
Regional And Mesoscale Meteorology Team
Daily Satellite Discussion
Tuesday November 4, 1997
GOES-9 10.7 micrometer image 1500 UTC 9 Oct 1997
(click to enlarge)
GOES-9 visible image 1500 UTC 9 Oct 1997
(click to enlarge)
Unusual IR cloud top pattern in the tropics. This is a continuation of the RAMMT Discussion of Oct. 17, which showed the "enhanced-V" signature in the IR imagery with the Jarrell, TX, tornado. With those and similar cases it appears that some of the overshooting cirrus with intense updrafts may reside long enough in the stratosphere to take on the environmental temperature above the tropopause inversion, and thus be warmer than nearby clouds at lower elevations. In general, deep convective updrafts in the tropics and also with tropical cyclones are much weaker than with tornadic thunderstorms. In addition, vertical wind shear is often very low. For those reasons, the "enhanced-V" is rarely observed in the tropics.

The matching IR and visible images (enhancements are used as shown by the graybars at the bottom of the images) show Hurricane Pauline, which is weakening rapidly and is centered just inland on the southwest coast of Mexico. Very intense convection is occurring just off shore with IR cloud top temperatures as cold as -88C. The pattern is similar to the enhanced-V pattern, in that there is a central area which is warmer than the surrounding anvil, because it has developed past the tropopause inversion. The smaller overshooting cores show up as cold spots. The mechanism to produce this pattern seems to be the same as with the enhanced-V of severe thunderstorms, except that cloud spreads in all directions instead of being advected downstream in a V shape pattern.

Ray Zehr

We welcome your comments and discussion at ramsdis@comet.ucar.edu

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