Aircraft distrails and contrails

December 30th, 2013 |
Suomi NPP VIIRS 0.64 µm visible channel and false-color RGB images

Suomi NPP VIIRS 0.64 µm visible channel and false-color RGB images

Two signatures of aircraft traffic sometimes seen in satellite imagery are (1) dissipation trails, or “distrails”, and (2) condensation trails, or “contrails”. On 30 December 2013, examples of both were seen over Virginia and West Virgina. Multiple layers of clouds existed over the region as a cold frontal boundary was moving eastward; ahead of the cold front patchy areas of low-level supercooled water droplet clouds were drifting northeastward across North Carolina and Virginia, and examples of aircraft distrails could be seen in a comparison of Suomi NPP VIIRS 0.64 µm visible channel and false-color Red/Green/Blue (RGB) images at 17:29 UTC (above). When aircraft penetrated the supercooled water droplet cloud deck, particles in their exhaust acted as ice condensation nuclei which then created narrow lines of glaciated (ice) clouds in their wake. One particularly vivid example of a distrail was oriented from southwest to northeast over central Virginia. Ice clouds appeared as varying shades of red in the RGB image, in contrast to supercooled water droplet clouds which showed up as brighter white features.

Farther to the west, a wide band of higher-altitude ice clouds existed as part of an elongated warm conveyor belt that was approaching the East Coast of the US. A comparison of Suomi NPP VIIRS 3.74 µm shortwave IR channel and 11.45 µm IR channel images at 17:29 UTC (below) revealed the presence of widespread contrails over much of West Virginia into western Virginia. The contrails were nearly as cold as the underlying high-altitude cirrus clouds on the 11.45 µm IR image, making their identification more difficult — however, the contrails were quite evident on the shortwave IR image, since their smaller particles were very efficient reflectors of solar radiation (making them exhibit a warmer, darker gray signature).

Suomi NPP VIIRS 3.74 µm shortwave IR and 11.45 µm IR channel images

Suomi NPP VIIRS 3.74 µm shortwave IR and 11.45 µm IR channel images

Other examples of aircraft distrails can be found in previous blog posts.

Valley fog in Kentucky, and aircraft “distrails” in South Carolina

December 5th, 2012 |
GOES-13 0.63 µm visible channel images (click image to play animation)

GOES-13 0.63 µm visible channel images (click image to play animation)

Two features of interest appeared on McIDAS images of GOES-13 0.63 µm visible channel data (above; click image to play animation) on the morning of 05 December 2012: (1) fingers of valley fog across much of Kentucky, which dissipated as daytime heating and boundary layer mixing increased, and (2) a pair of aircraft dissipation trails (or “distrails”) that first appeared north of Sumter (KSSC) and drifted east-northeastward between Florence (KFLO) and Darlington (KUDG). It is likely that these distrails (highlighted with yellow ‘>’ symbols) formed as aircraft heading to or from Columbia, South Carolina (KCAE) passed through the supercooled water droplet cloud layer, causing glaciation and subsequent fallout of the ice crystals to create the elongated clearing lines.

Hole punch clouds and aircraft distrails over Georgia and South Carolina

February 17th, 2012 |
GOES-13 0.63 µm visible channel images

GOES-13 0.63 µm visible channel images

McIDAS images of 1-km resolution GOES-13 0.63 µm visible channel data (above) showed that there were a number of “hole punch clouds” and long “aircraft dissipation trails” (or “distrails”) drifting east-northeastward over eastern Georgia and the northern half of South Carolina on 17 February 2012. These features occur when aircraft ascend or descend through a cloud layer composed of supercooled water droplets — particles from the jet engine exhaust act as ice nuclei that initiate glaciation. The resulting relatively large ice crystals then begin to fall out of the supercooled water droplet cloud layer, causing the hole punch or aircraft dissipation trail to appear.

A closer view using a 250-meter resolution Terra MODIS true-color Red/Green/Blue (RGB) image from the SSEC MODIS Today site (below; viewed using Google Earth) shows more structural details of some of the hole punch and distrail features at 15:47 UTC (10:47 am local time). The aircraft likely penetrated the supercooled water droplet cloud over Georgia, after which the hole punch and distrail signatures grew as the cloud drifted east-northeastwrad over South Carolina.

MODIS true color Red/Green/Blue (RGB) image (viewed using Google Earth)

MODIS true color Red/Green/Blue (RGB) image (viewed using Google Earth)

A comparison of 250-meter resolution Terra MODIS true-color and false-color Red/Green/Blue (RGB) images (below) helps to verify that the hole punch and distrail features were indeed composed of ice crystals (which appear as cyan on the false-color image, in contrast to the brighter white supercooled water droplet cloud features).

MODIS true-color and false-color Red/Green/Blue (RGB) images

MODIS true-color and false-color Red/Green/Blue (RGB) images

Aircraft “distrails” over the southcentral US

January 29th, 2007 |

GOES-12 visible image

GOES-12 visible channel imagery (above; Java animation) revealed numerous aircraft dissipation trails (otherwise known as “distrails” or “hole punch clouds”) during the day over eastern Texas, northern Louisiana, southern Arkansas, and Mississippi on 29 January 2007. Corresponding GOES-12 10.7µm InfraRed (IR) imagery showed that cloud top temperatures over that region were generally between -20º and -35º C; as aircraft (likely air traffic to/from Dallas-Fort Worth airport KDFW) penetrated that supercooled cloud layer aloft, they caused the cloud droplets to glaciate and begin to fall out of the cloud (causing the “holes” and “streaks” that were evident on the visible imagery). A higher resolution view of these cloud features is available from the Terra MODIS (sourced from the NASA Rapidfire site) and Aqua MODIS overpasses. The 12 UTC rawinsonde data from Fort Worth, Texas (below) indicated that the likely elevation of the supercooled coud deck was probably around 25,000 feet or so. Photos of these cloud features can be seen on the MediaLine weather forum, Weather Underground WunderBlog, WKRG (Mobile AL), NASA Earth Observatory , and StormCenter Envirocast sites.
Fort Worth TX rawinsonde report