NOAA-NESDIS
Regional And Mesoscale Meteorology Team
Daily Satellite Discussion
Thursday June 26, 1997
Fig. 1 (NOAA GOES-8 Channel 4, 10.7 microns)
Fig. 2 (NOAA GOES-8 Channel 4, 10.7 microns)
Today's feature looks at composites of maximum, minimum and averaged radiance values for 10.7 micron images centered over Central America for 0015 and 1315 GMT during the period 1-15 June 1997. The normal 10.7 micron enhancement table has been rolled to highlight temperatures below 0C. Notice that just after sunset (0015 GMT) the average composite indicates that convective activity was predominantly over land areas and that cloud top brightness temperatures varied between -20C to -40C. There was very little convective activity in the upper right portion of the image over the Caribbean Sea where temperatures averaged between 10C to 25C (Fig. 1). At 1315 GMT, just after sunrise (Fig. 2), the average image indicates less overall convective activity and a somewhat reversed pattern of activity from the 0015 GMT image. The coldest regions were located just off the coast line, particularly in the bottom portion of the image, while land regions were much warmer than in the 0015 GMT image, indicating less cloud coverage at that time. Note also that the upper right portion of this image, like the 1315 GMT image, there was very little cloud coverage. For the tropics, this quick view of averaged images supports the notion of convection over land during the day and over water at night.
Fig. 3 (NOAA GOES-8 Channel 4, 10.7 microns)
Fig. 4 (NOAA GOES-8 Channel 4, 10.7 microns)
The average image is one tool that can be used in developing a satellite climatology for a region. It can indicate persistent clear and cloudy areas on a diurnal time scale. In data sparse areas, this information can also give an indication of the validity of precipitation and solar radiation estimates. As with climatological averages of station air temperatures, this information represents what occurred at a given location over time and should be interpreted carefully. Compare the average images with the composite maximum radiance seen in Fig. 3 and Fig. 4 (warmest brightness temperature) and composite minimum radiance seen in Fig. 5 and Fig. 6 (coldest brightness temperature) for the same time period. Note that in these images, the color enhancement has been shifted to highlight temperatures colder than -30C. The maximum radiance composite for 0015 GMT indicates that there were areas during this 15-day period that were never cloud free while the 1315 GMT image indicates that cloud free conditions were more prevalent. The minimum radiance composite (coldest brightness temperatures) tends to pick out individual convective elements over the 15-dat time period. Note that these images also tend to show the pattern of convective development over land during the day and over the water at night.
Fig. 5 (NOAA GOES-8 Channel 4, 10.7 microns)
Fig. 6 (NOAA GOES-8 Channel 4, 10.7 microns)

Bernadette Connell

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