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GOES-16 Mountain Wave clouds on 3 March 2017

Posted On: March 3, 2017 - By: Dan Bikos


The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing.  Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.

Mountain wave (orographic cirrus) clouds were observed in the Rocky Mountain region on the morning of 3 March 2017 as observed in this 10.35 micron image:

annotation_20170303

 

Let’s examine a series of loops of different channels available from GOES-16.  The loops will span through sunrise (i.e., start in darkness and transition to daytime).

The familiar IR channel at 10.35 microns has always been a good channel for identifying mountain wave clouds and will continue to be an ideal channel for identification:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/3mar17/B13&loop_speed_ms=80

The mountain wave clouds in western Montana develop during the loop while the mountain wave clouds downwind of the Bighorn range in north central Wyoming dissipate during the loop.  Mountain wave clouds are easily identified since brightness temperatures are particularly cold, making them stand out when compared, for example, to the clouds associated with the disturbance passing from eastern Montana into western North Dakota.  Mountain wave clouds in north central Colorado exist at the beginning of the loop and expand in time.

One of the new channels on GOES-R is the 1.38 micron channel (“Cirrus band”), which is useful for identifying mountain wave clouds since cirrus clouds stand out while low-level level clouds do not:

 http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/3mar17/B04&loop_speed_ms=80

Next we will look at the 3 water vapor channels available on GOES-R.

First, the upper-level water vapor band at 6.2 microns:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/3mar17/B08&loop_speed_ms=80

Next, the mid-level water vapor band at 6.9 microns:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/3mar17/B09&loop_speed_ms=80

Finally, the low-level water vapor band at 7.3 microns:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/3mar17/B10&loop_speed_ms=80

What additional information do the water vapor bands show?

The water vapor bands typically have a subsidence signature (relatively warmer brightness temperatures) slightly upwind (i.e., west in this case) of the mountain wave clouds.  This subsidence signature can be seen on all 3 water vapor channels, but it’s more subtle in the upper-level water vapor imagery.  The depth of the subsidence can be assessed by looking at all 3 channels in tandem.  It may be worthwhile noting trends in the subsidence signature for the mountains in your forecast area during these mountain wave cloud events.

Our last loop will be a channel difference product, the 3.9 minus 11.2 micron loop, commonly known as the fog / low-stratus product since it’s been around for a long time with current GOES channels.  Since this product involves the 3.9 micron channel, we have to be aware of the solar reflected component during the daytime hours.  This can easily be tracked before and after sunset in this loop:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/3mar17/fog&loop_speed_ms=80

Recall from this training session that mountain wave clouds tend to be composed of relatively small ice crystals which are highly reflective.  By subtracting out the emitted component we are left with the solar reflected component during the daytime, this helps make the mountain wave clouds stand out from other clouds.


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