Interesting circular contrail over South DakotaMulti-panel images of all 16 ABI spectral bands from GOES-16 (GOES-East) (above) revealed an interesting circular contrail over northeastern South Dakota on 29 January 2020. A signature of this contrail was evident in all 16 bands — visible, near-infrared and infrared. This feature was likely formed by a military aircraft performing training exercises over the area.
A sequence of GOES-16 ABI spectral band images covering that same 1751-2001 UTC time period (below) provided a larger view of the circular contrail — whose diameter was about 10-12 miles — along with a linear contrail located about 30 miles to the southwest.A toggle between GOES-16 “Red” Visible (0.64 µm) and Near-Infrared “Cirrus” (1.37 µm) images at 1911 UTC (below) showed that the darker signature seen in the Visible imagery was a shadow cast by the higher-altitude contrail onto the top of the low-altitude stratus clouds. A similar northwestward shadow offset (of about 5 miles) was apparent with the linear contrail feature. The southwestward shift of the higher-altitude contrail (with respect to the surface shadow) was not due to parallax — this webapp shows that the direction of parallax shift over that region would be northwestward for cloud features at altitudes of 15,000 feet and 30,000 feet (below). Plots of rawinsonde data from Aberdeen, South Dakota (below) showed an increase in moisture during the day within the 500-300 hPa layer — due to its relatively slow southeastward propagation, the circular contrail likely existed within the lower portion of that layer (where wind speeds were less). A signature of the circular contrail was seen in all 3 of the GOES-16 Water Vapor spectral bands — weighting functions derived using rawinsonde data from Aberdeen, South Dakota (below) showed either primary or secondary peaks within the 500-300 hPa layer. Thanks go out to Jay Trobec (@trobec), KELOLAND TV in Sioux Falls, for alerting us about this interesting example.