Detecting ship condensation trails in the Gulf of Alaska
POES AVHRR images and derived cloud products
A comparison of AWIPS images of the 1-km resolution POES AVHRR 0.86 µm visible channel, 12.0 µm IR channel, Cloud Top Temperature product, Cloud Type product, Cloud Top Height product, Cloud Optical Depth product, and Cloud Particle Effective Radius product (above) demonstrated that the Cloud Particle Effective Radius product was the best tool to use in locating the pattern of ship condensation trails (or “ship tracks”) that was located over the northern Gulf of Alaska on 19 November 2010.
The Cloud Type of the stratus cloud deck where the ship tracks were seen was primarily of the “supercooled” classification (green color enhancement), with Cloud Top Temperatures generally in the -3º to -4º C range and Cloud Top Heights of 2-3 km. According to the Cloud Particle Effective Radius product, the size of the particles within the ship track features was about 23-25 µm — somewhat smaller than the 27-31 µm in the surrounding undisturbed stratus cloud deck. This is evidence of the “Twomey effect”, where sulfate aerosols (found in the exhaust plumes of the diesel-burning ships) act as cloud condensation nuclei, which leads to greater numbers of smaller cloud droplets.
As part of the CIMSS involvement in GOES-R Proving Ground activities, POES AVHRR satellite images and products are currently being made available in an AWIPS format for interested NWS forecast offices to add to their local AWIPS workstations (via LDM subscription). For more information, see the AVHRR Imagery and Products in D-2D site. A VISIT training lesson has also been created for these AVHRR images and products.