RAMMB Satellite Case Studies

What the GOES imagery shows us over Colorado & Kansas

Upper-level tropospheric disturbances are characterized by alternate regions of upward and downward motion. Because the atmosphere warms (cools) as it subsides (ascends), the 6.7 micron imagery channel (which is sensitive to the temperature of upper level water vapor) can be used to identify and track such features. Study the animated 6.7 micron imagery and try to locate shortwave signatures approaching the area of interest. Larger-scale features such as jet streams are also indicated by this imagery. They often appear as sharp gradients in brightness temperatures on a large scale. Can you find the subtropical jet?

Which, if any, lower-tropospheric features can be seen using the 6.7 m imagery? This channel is sensitive to water vapor at mid- to upper-levels, as well as to cold upper-level cloudiness. Thus, we should not expect to see lower-level atmospheric phenomenon. Careful perusal of sequential imagery from this period shows features that seem to be associated with the high terrain of the Rocky Mountains. Can you explain this apparent contradiction? For information on this, as well as the other 4 imaging channels, refer to the CIRA-RAMM Team's Introduction to the GOES-8 Imager tutorial.

Use sequential, 10.7 micron imagery to study the squall line which occurs overnight in Nebraska and South Dakota. Obviously, rain-stabilized air (i.e., low-level outflow) is being left behind by these storms, but is not observable over most of the region due to overlying anvil cirrus. However, the area at the south end of the line is not anvil-covered. (Is an outflow boundary being left behind in this region?) If it is, why can't we see it?

Now observe the same sequence using the "fog product" imagery (found in AREAs 6908-6944). The fog product is made by differencing the 3.9 and the 10.7 micron channels, and is sensitive to water clouds (show as light gray in the enhancement used here). Notice the line of lighter gray clouds to the south and west of the squall line. These are stratiform clouds forming along and above the outflow airmass, and can be seen quite clearly in this product. The boundary is not as easy to see on the 10.7 micron channel, since the actual temperature of the cold ground and stratiform clouds are similar. (10.7 micron is a window channel which senses the actual tempertures of viewed scenes.) What is influencing the extent/coverage of this cloud mass? Is terrain influencing the shape of this cloud area? For an in-depth discussion of this useful product, refer to the CIRA-RAMM Team's GOES' 3.9 micron Channel tutorial.

The outflow boundary, once identified, can be followed into the morning hours on visible imagery. Track the location of this feature for as long as you can. HINT: look for differences in cloud type on either side of the feature. Which channels, if any, can be used to differentiate cloud type? Much of the stratiform cloudiness dissipates shortly after sunrise. What happens to the cloud fields near this boundary after the low clouds dissipate? What clues can you see in the imagery to confirm whether or not the outflow boundary is still present?

Mean sea-level pressure analyses from NCEP continued to analyze a generally north-south oriented warm front in eastern Oklahoma and Kansas throughout the day. This front may be seen on the introduction page to this section. While a distinct boundary could be followed using surface observations, no clearly identifiable cloud line can be seen on GOES imagery. Why is this? What ramifications does this factor have for later convection? HINT: Initial insolation may be evaporating surface moisture from overnight precipitation. Is this likely in these areas from what can be seen in the satellite imagery? Once a cloudy region clears off, what differences would you expect to find in skin temperature values in 10.7 micron imagery between it and regions which were not cloudy? Will air temperatures reflect these differences immediately?