Traffic camera view of contrails from Mesa, AZ, courtesy Arizona Department of Transportation. Full Resolution
This morning there were a lot of contrails evident on the GOES-16 data. Looking at the VEF 12Z 10 APR 2017 sounding (see below), conditions look good for them – lots of high-level moisture. From this, we expect most of the contrails to be in the 200-300 mb (which is around a cruising altitude of ~30,000 ft).
Of course we can’t see the contrails until the sun comes up in the visible and near-IR bands. However, using the different water vapor bands, we can still see them (the improved resolution helps too!). Using this website to learn about weighting functions, we can get a general idea of the level at which the weighting function for each water vapor channel peaks. Since contrails are typically located high in the troposphere, they will appear similarly visible in all three water vapor channels. In other words, most water vapor absorption for the three water vapor channels (see weighting functions below) takes place below the level at which a typical contrail will be located. The 7.34 um channel will be slightly better than the other two water vapor channels at detecting upper level cloud features such as contrails since it is the least sensitive to water vapor absorption.
The “split-window” (10.35 – 12.3) moisture difference does an especially good job at detecting high, thin clouds such as contrails:
Once the sun does come up, we can use our other bands. In this loop, I have the Red Band (Ch 2, 0.64 um) in the top-left, the Cirrus Band (Ch 4, 1.38 um) in the top-right, and the Snow/Ice Band (Ch 5, 1.61 um) in the bottom-right. First thing I notice is that the contrails don’t show up the best in the Red Band, the Cirrus band pops them the best. According to the GOES-R ABI Fact Sheet for the Cirrus Band,
The “cirrus” near-infrared band at 1.37 μm will detect very thin cirrus clouds during the day. This band is centered in a strong water vapor absorption spectral region. It does not routinely sense the lower troposphere, where there is substantial water vapor, and thus provides excellent daytime sensitivity to high, very thin cirrus under most circumstances, especially in warm, moist atmospheres.
Thus the high-clouds pop against a muted background of the lower troposphere. If you watch this loop, you can also see the contrails increase in abundance as we progress from 12Z through 1530Z. That is due to the increase in air traffice, which is confirmed with this loop (from Planefinder.net).
Thanks for reading!
Paul Iniguez (SOO-Phoenix WFO)
Post edited on 4/16 (Bill Line, NWS)
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